Merge remote-tracking branch 'origin/feature/matador-ng' into feature/matador-ng

This reverts commit 8914c06833.

backends/postgres/include/postgres_connection.hpp

@@ -33,22 +33,26 @@ public:
 
   utils::result<sql::execute_result, utils::error> execute(const sql::query_context &context) override;
   utils::result<std::unique_ptr<sql::statement_impl>, utils::error> prepare(const sql::query_context &context) override;
-  utils::result<std::unique_ptr<sql::query_result_impl>, utils::error> fetch(const sql::query_context &context) override;
+  utils::result<std::unique_ptr<sql::query_result_impl>, utils::error> fetch(const sql::query_context &ctx) override;
 
   utils::result<std::vector<object::attribute>, utils::error> describe(const std::string& table) override;
   utils::result<bool, utils::error> exists(const std::string &schema_name, const std::string &table_name) override;
 
+  utils::result<bool, utils::error> sequence_exists(const std::string &schema_name, const std::string &sequence_name) override;
+
   [[nodiscard]] std::string to_escaped_string( const utils::blob_type_t& value ) const override;
 
 private:
-  [[nodiscard]] static std::string generate_statement_name(const sql::query_context &query) ;
+  [[nodiscard]] static std::string generate_statement_name(const sql::query_context &ctx) ;
+
+  [[nodiscard]] utils::result<sql::execute_result, utils::error> execute(const std::string &stmt) const;
 
 private:
   PGconn *conn_{nullptr};
 
-  using string_to_int_map = std::unordered_map<std::string, unsigned long>;
+  using hash_to_string_map = std::unordered_map<size_t, std::string>;
 
-  static string_to_int_map statement_name_map_;
+  static hash_to_string_map statement_name_map_;
 };
 
 }

backends/postgres/src/postgres_connection.cpp

@@ -7,14 +7,15 @@
 
 #include "matador/sql/error_code.hpp"
 #include "matador/sql/record.hpp"
-
 #include "matador/sql/internal/query_result_impl.hpp"
 
+#include "matador/utils/string.hpp"
+
 #include <algorithm>
 #include <sstream>
 
 namespace matador::backends::postgres {
-postgres_connection::string_to_int_map postgres_connection::statement_name_map_{};
+postgres_connection::hash_to_string_map postgres_connection::statement_name_map_{};
 
 postgres_connection::postgres_connection(const sql::connection_info &info)
 : connection_impl(info) {
@@ -34,7 +35,7 @@ utils::result<void, utils::error> postgres_connection::open() {
     const std::string msg = PQerrorMessage(conn_);
     PQfinish(conn_);
     conn_ = nullptr;
-    return utils::failure(make_error(sql::error_code::OPEN_ERROR, nullptr, conn_, "Failed to connect"));
+    return utils::failure(make_error(sql::error_code::OpenError, nullptr, conn_, "Failed to connect"));
   }
 
   return utils::ok<void>();
@@ -70,7 +71,7 @@ utils::result<utils::version, utils::error> postgres_connection::server_version(
   const auto server_version = PQserverVersion(conn_);
 
   if (server_version == 0) {
-    return utils::failure(make_error(sql::error_code::FAILURE, nullptr, conn_, "Failed to get server version"));
+    return utils::failure(make_error(sql::error_code::Failure, nullptr, conn_, "Failed to get server version"));
   }
 
   return utils::ok(utils::version{
@@ -82,20 +83,20 @@ utils::result<utils::version, utils::error> postgres_connection::server_version(
 
 utils::basic_type oid2type(Oid oid);
 
-utils::result<std::unique_ptr<sql::query_result_impl>, utils::error> postgres_connection::fetch(const sql::query_context &context) {
+utils::result<std::unique_ptr<sql::query_result_impl>, utils::error> postgres_connection::fetch(const sql::query_context &ctx) {
-  PGresult *res = PQexec(conn_, context.sql.c_str());
+  PGresult *res = PQexec(conn_, ctx.sql.c_str());
 
   if (is_result_error(res)) {
-    const auto err = make_error(sql::error_code::FETCH_FAILED, res, conn_, "Failed to fetch", context.sql);
+    const auto err = make_error(sql::error_code::FetchFailed, res, conn_, "Failed to fetch", ctx.sql);
     PQclear(res);
     return utils::failure(err);
   }
 
-  std::vector<object::attribute> prototype = context.prototype;
+  std::vector<object::attribute> prototype = ctx.prototype;
 
   const int num_col = PQnfields(res);
   if (prototype.size() != static_cast<size_t>(num_col)) {
-    const auto err = make_error(sql::error_code::FETCH_FAILED, res, conn_, "Number of received columns doesn't match expected columns.", context.sql);
+    const auto err = make_error(sql::error_code::FetchFailed, res, conn_, "Number of received columns doesn't match expected columns.", ctx.sql);
     PQclear(res);
     return utils::failure(err);
   }
@@ -111,22 +112,32 @@ utils::result<std::unique_ptr<sql::query_result_impl>, utils::error> postgres_co
 
   return utils::ok(std::make_unique<sql::query_result_impl>(std::make_unique<postgres_result_reader>(res),
                                                                     std::move(prototype),
-                                                                    context.resolver,
+                                                                    ctx.resolver,
-                                                                    context.result_type));
+                                                                    ctx.result_type));
 }
 
-std::string postgres_connection::generate_statement_name(const sql::query_context &query) {
+std::string postgres_connection::generate_statement_name(const sql::query_context &ctx) {
-  std::stringstream name;
+  auto it = statement_name_map_.find(ctx.sql_hash);
-  name << query.table_name << "_" << query.command_name;
-  auto result = statement_name_map_.find(name.str());
 
-  if (result == statement_name_map_.end()) {
+  if (it == statement_name_map_.end()) {
-    result = statement_name_map_.insert(std::make_pair(name.str(), 0)).first;
+    it = statement_name_map_.insert(std::make_pair(ctx.sql_hash, utils::to_hex_string(ctx.sql_hash))).first;
   }
 
-  name << "_" << ++result->second;
+  return it->second;
+}
 
-  return name.str();
+utils::result<sql::execute_result, utils::error> postgres_connection::execute(const std::string& stmt) const {
+    PGresult *res = PQexec(conn_, stmt.c_str());
+
+    if (const auto status = PQresultStatus(res); status != PGRES_COMMAND_OK && status != PGRES_TUPLES_OK) {
+        return utils::failure(make_error(sql::error_code::Failure, res, conn_, "Failed to execute", stmt));
+    }
+
+    const size_t affected_rows = utils::to<size_t>(PQcmdTuples(res));
+
+    PQclear(res);
+
+    return utils::ok(sql::execute_result{affected_rows});
 }
 
 utils::result<std::unique_ptr<sql::statement_impl>, utils::error> postgres_connection::prepare(const sql::query_context &context) {
@@ -135,7 +146,7 @@ utils::result<std::unique_ptr<sql::statement_impl>, utils::error> postgres_conne
   PGresult *result = PQprepare(conn_, statement_name.c_str(), context.sql.c_str(), static_cast<int>(context.bind_vars.size()), nullptr);
 
   if (is_result_error(result)) {
-    return utils::failure(make_error(sql::error_code::PREPARE_FAILED, result, conn_, "Failed to prepare", context.sql));
+    return utils::failure(make_error(sql::error_code::PrepareFailed, result, conn_, "Failed to prepare", context.sql));
   }
 
   std::unique_ptr<sql::statement_impl> s(std::make_unique<postgres_statement>(conn_, result, statement_name, context));
@@ -143,13 +154,11 @@ utils::result<std::unique_ptr<sql::statement_impl>, utils::error> postgres_conne
 }
 
 utils::result<sql::execute_result, utils::error> postgres_connection::execute(const sql::query_context &context) {
-  if (context.command == sql::sql_command::Insert) {
+  return execute(context.sql);
-    // handle insert command with the primary key generator strategy
-  }
   PGresult *res = PQexec(conn_, context.sql.c_str());
 
   if (const auto status = PQresultStatus(res); status != PGRES_COMMAND_OK && status != PGRES_TUPLES_OK) {
-    return utils::failure(make_error(sql::error_code::FAILURE, res, conn_, "Failed to execute", context.sql));
+    return utils::failure(make_error(sql::error_code::Failure, res, conn_, "Failed to execute", context.sql));
   }
 
   const size_t affected_rows = utils::to<size_t>(PQcmdTuples(res));
@@ -244,7 +253,7 @@ utils::result<std::vector<object::attribute>, utils::error> postgres_connection:
   PGresult *res = PQexec(conn_, stmt.c_str());
 
   if (is_result_error(res)) {
-    return utils::failure(make_error(sql::error_code::DESCRIBE_FAILED, res, conn_, "Failed to describe", stmt));
+    return utils::failure(make_error(sql::error_code::DescribeFailed, res, conn_, "Failed to describe", stmt));
   }
 
   postgres_result_reader reader(res);
@@ -269,7 +278,7 @@ utils::result<std::vector<object::attribute>, utils::error> postgres_connection:
       null_opt = object::null_option_type::NotNull;
     }
     // f.default_value(res->column(4));
-    prototype.emplace_back(name, type, utils::null_attributes, null_opt);
+    prototype.emplace_back(name, type, NullAttributes, null_opt);
   }
 
   return utils::ok(prototype);
@@ -285,19 +294,33 @@ utils::result<bool, utils::error> postgres_connection::exists(const std::string
   PGresult *res = PQexec(conn_, stmt.c_str());
 
   if (is_result_error(res)) {
-    return utils::failure(make_error(sql::error_code::TABLE_EXISTS_FAILED, res, conn_, "Failed check if table exists", stmt));
+    return utils::failure(make_error(sql::error_code::TableExistsFailed, res, conn_, "Failed check if table exists", stmt));
   }
 
   const auto result = utils::to<size_t>(PQcmdTuples(res));
   if (!result) {
     PQclear(res);
-    return utils::failure(make_error(sql::error_code::FAILURE, res, conn_, "Failed to convert result value", stmt));
+    return utils::failure(make_error(sql::error_code::Failure, res, conn_, "Failed to convert result value", stmt));
   }
 
   PQclear(res);
   return utils::ok(*result == 1);
 }
 
+utils::result<bool, utils::error> postgres_connection::sequence_exists(const std::string& schema_name, const std::string& sequence_name) {
+    const std::string sql{"SELECT to_regclass('" + schema_name + "." + sequence_name + "')"};
+    PGresult* res = PQexec(conn_, sql.c_str());
+
+    if (PQresultStatus(res) != PGRES_TUPLES_OK) {
+        return utils::failure(make_error(sql::error_code::SequenceExistsFailed, res, conn_, "Failed check if sequence exists", sql));
+    }
+
+    const bool exists = PQgetisnull(res, 0, 0) ? false : true;
+    PQclear(res);
+
+    return utils::ok(exists);
+}
+
 std::string postgres_connection::to_escaped_string(const utils::blob_type_t &value) const {
   size_t escapedDataLength;
   unsigned char *escapedData = PQescapeByteaConn(conn_, value.data(), value.size(), &escapedDataLength);

backends/postgres/src/postgres_error.cpp

@@ -6,7 +6,10 @@
 
 namespace matador::backends::postgres {
 
-utils::error make_error(const sql::error_code ec, const PGresult *res, const PGconn *db, const std::string &msg,
+utils::error make_error(const sql::error_code ec,
+                        const PGresult *res,
+                        const PGconn *db,
+                        const std::string &msg,
                         const std::string &sql) {
   utils::error err(ec, msg);
   err.add_error_info("dbms", "postgres");
@@ -30,22 +33,19 @@ bool is_result_error(const PGresult *res) {
   return status != PGRES_TUPLES_OK && status != PGRES_COMMAND_OK;
 }
 
-void throw_postgres_error(const char *what, const std::string &source)
+void throw_postgres_error(const char *what, const std::string &source) {
-{
   std::stringstream msg;
   msg << "postgres error (" << source << "): " << what;
   throw std::logic_error(msg.str());
 }
 
-void throw_postgres_error(PGconn *db, const std::string &source)
+void throw_postgres_error(const PGconn *db, const std::string &source) {
-{
   if (PQstatus(db) == CONNECTION_BAD) {
     throw_postgres_error(PQerrorMessage(db), source);
   }
 }
 
-void throw_postgres_error(PGresult *res, PGconn *db, const std::string &source, const std::string &sql)
+void throw_postgres_error(const PGresult *res, const PGconn *db, const std::string &source, const std::string &sql) {
-{
   if (res == nullptr) {
     std::stringstream msg;
     msg << "postgres error (" << source << ", " << PQerrorMessage(db) << ": " << sql;

backends/postgres/src/postgres_statement.cpp

@@ -21,7 +21,7 @@ postgres_statement::~postgres_statement() {
 utils::result<sql::execute_result, utils::error> postgres_statement::execute(const sql::parameter_binder& bindings) {
   const auto* postgres_bindings = dynamic_cast<const postgres_parameter_binder*>(&bindings);
   if (!postgres_bindings) {
-    return utils::failure(utils::error(sql::error_code::EXECUTE_FAILED, "Failed to cast bindings to postgres bindings"));
+    return utils::failure(utils::error(sql::error_code::ExecuteFailed, "Failed to cast bindings to postgres bindings"));
   }
 
   if (query_.command == sql::sql_command::Insert) {
@@ -37,7 +37,7 @@ utils::result<sql::execute_result, utils::error> postgres_statement::execute(con
       0);
 
   if (is_result_error(res)) {
-    return utils::failure(make_error(sql::error_code::EXECUTE_FAILED, res, db_, "Failed to execute statement", query_.sql));
+    return utils::failure(make_error(sql::error_code::ExecuteFailed, res, db_, "Failed to execute statement", query_.sql));
   }
 
   size_t value{0};
@@ -53,7 +53,7 @@ utils::result<sql::execute_result, utils::error> postgres_statement::execute(con
 utils::result<std::unique_ptr<sql::query_result_impl>, utils::error> postgres_statement::fetch(const sql::parameter_binder& bindings) {
   const auto* postgres_bindings = dynamic_cast<const postgres_parameter_binder*>(&bindings);
   if (!postgres_bindings) {
-    return utils::failure(utils::error(sql::error_code::EXECUTE_FAILED, "Failed to cast bindings to postgres bindings"));
+    return utils::failure(utils::error(sql::error_code::ExecuteFailed, "Failed to cast bindings to postgres bindings"));
   }
   PGresult *res = PQexecPrepared(db_,
       name_.c_str(),
@@ -64,7 +64,7 @@ utils::result<std::unique_ptr<sql::query_result_impl>, utils::error> postgres_st
       0);
 
   if (is_result_error(res)) {
-    return utils::failure(make_error(sql::error_code::FETCH_FAILED, res, db_, "Failed to fetch statement", query_.sql));
+    return utils::failure(make_error(sql::error_code::FetchFailed, res, db_, "Failed to fetch statement", query_.sql));
   }
 
   return utils::ok(std::make_unique<sql::query_result_impl>(std::make_unique<postgres_result_reader>(res),

backends/postgres/test/CMakeLists.txt

@@ -1,18 +1,15 @@
-CPMAddPackage("gh:catchorg/Catch2@3.7.1")
+CPMAddPackage("gh:catchorg/Catch2@3.14.0")
 
 list(APPEND CMAKE_MODULE_PATH ${catch2_SOURCE_DIR}/extras)
 
-set(POSTGRES_CONNECTION_STRING "postgres://test:test123!@127.0.0.1:15442/matador")
+#set(POSTGRES_CONNECTION_STRING "postgres://test:test123!@127.0.0.1:15442/matador")
-#set(POSTGRES_CONNECTION_STRING "postgres://test:test123!@127.0.0.1:5432/matador")
+set(POSTGRES_CONNECTION_STRING "postgres://test:test123!@127.0.0.1:5432/matador")
 
 configure_file(Connection.hpp.in ${PROJECT_BINARY_DIR}/backends/postgres/test/connection.hpp @ONLY IMMEDIATE)
 
 message(STATUS "postgresql connection string: ${POSTGRES_CONNECTION_STRING}")
 
 set(TEST_SOURCES
-  ../../../test/models/coordinate.hpp
-  ../../../test/models/location.hpp
-  ../../../test/models/types.hpp
   ../../../test/backends/ColorEnumTraits.cpp
   ../../../test/backends/ColorEnumTraits.hpp
   ../../../test/backends/ConnectionTest.cpp
@@ -25,15 +22,32 @@ set(TEST_SOURCES
   ../../../test/backends/SchemaFixture.cpp
   ../../../test/backends/SchemaFixture.hpp
   ../../../test/backends/SchemaTest.cpp
+  ../../../test/backends/SequenceFixture.cpp
+  ../../../test/backends/SequenceFixture.hpp
+  ../../../test/backends/SequenceTest.cpp
+  ../../../test/backends/SessionDeleteHasMany.cpp
+  ../../../test/backends/SessionDeleteHasManyToMany.cpp
   ../../../test/backends/SessionFixture.cpp
   ../../../test/backends/SessionFixture.hpp
+  ../../../test/backends/SessionInsertBelongsTo.cpp
+  ../../../test/backends/SessionInsertHasMany.cpp
+  ../../../test/backends/SessionInsertHasManyToManyTest.cpp
+  ../../../test/backends/SessionInsertHasOne.cpp
   ../../../test/backends/SessionTest.cpp
   ../../../test/backends/StatementCacheTest.cpp
   ../../../test/backends/StatementTest.cpp
+  ../../../test/backends/TableSequenceFixture.cpp
+  ../../../test/backends/TableSequenceFixture.hpp
+  ../../../test/backends/TableSequenceTest.cpp
   ../../../test/backends/TypeTraitsTest.cpp
-  ../../../test/utils/record_printer.hpp
+  ../../../test/models/author.hpp
-  ../../../test/utils/record_printer.cpp
+  ../../../test/models/coordinate.hpp
+  ../../../test/models/location.hpp
   ../../../test/models/model_metas.hpp
+  ../../../test/models/types.hpp
+  ../../../test/models/user.hpp
+  ../../../test/utils/RecordPrinter.cpp
+  ../../../test/utils/RecordPrinter.hpp
 )
 
 set(LIBRARY_TEST_TARGET PostgresTests)

demo/CMakeLists.txt

@@ -1,4 +1,5 @@
-add_executable(demo main.cpp)
+add_executable(demo main.cpp
+  ../include/matador/query/query_column.hpp)
 
 target_link_libraries(demo PRIVATE
   matador-core

demo/author.hpp

@@ -20,14 +20,15 @@ struct author {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::primary_key( op, "id", id );
-        field::attribute( op, "first_name", first_name, 63 );
+        field::attribute( op, "first_name", first_name, VarChar63 );
-        field::attribute( op, "last_name", last_name, 63 );
+        field::attribute( op, "last_name", last_name, VarChar63 );
-        field::attribute( op, "date_of_birth", date_of_birth, 31 );
+        field::attribute( op, "date_of_birth", date_of_birth, VarChar63 );
         field::attribute( op, "year_of_birth", year_of_birth );
         field::attribute( op, "distinguished", distinguished );
-        field::has_many( op, "books", books, "author_id", matador::utils::CascadeNoneFetchLazy );
+        field::has_many( op, "books", books, "author_id", utils::CascadeNoneFetchLazy );
     }
 };
 }

demo/book.hpp

@@ -15,10 +15,11 @@ struct book {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::primary_key( op, "id", id );
-        field::attribute( op, "title", title, 511 );
+        field::attribute( op, "title", title, VarChar511 );
-        field::belongs_to( op, "author_id", book_author, matador::utils::CascadeNoneFetchLazy );
+        field::belongs_to( op, "author_id", book_author, utils::CascadeNoneFetchLazy );
         field::attribute( op, "published_in", published_in );
     }
 };

demo/main.cpp

@@ -190,7 +190,7 @@ int main() {
   mc.date_of_birth = "19.8.1954";
   mc.year_of_birth = 1954;
   mc.distinguished = true;
-  auto insert_authors_sql = query::insert()
+  auto insert_authors_sql = insert()
     .into(AUTHOR)
     .values(mc)
     .execute(*c);
@@ -201,7 +201,7 @@ int main() {
     return 0;
   }
 
-  auto authors_result = query::select(AUTHOR)
+  auto authors_result = select(AUTHOR)
     .from(AUTHOR)
     .fetch_all(*c);
 
@@ -243,8 +243,8 @@ int main() {
   //  .values( {3, "Misery", mc.id, 1984} )
   //  .execute();
   //
-  // auto select_books_sql = query::select( BOOK, {AUTHOR.last_name} )
+  // auto select_books_sql = select( BOOK, {AUTHOR.last_name} )
-  auto select_books_sql = query::select({BOOK.id, BOOK.title, BOOK.author_id, BOOK.published_in, AUTHOR.last_name})
+  auto select_books_sql = select({BOOK.id, BOOK.title, BOOK.author_id, BOOK.published_in, AUTHOR.last_name})
     .from(BOOK)
     .join_left(AUTHOR)
     .on(BOOK.author_id == AUTHOR.id)
@@ -288,17 +288,17 @@ int main() {
   //
   // std::cout << "SQL: " << drop_authors_sql << "\n";
   //
-  auto res = query::select({PAYLOAD.id})
+  auto res = select({PAYLOAD.id})
     .from(PAYLOAD)
     .join_left(JOB)
     .on(JOB.payload == PAYLOAD.id)
     .where(
-      in(PAYLOAD.id, query::select({JOB.state})
+      in(PAYLOAD.id, select({JOB.state})
          .from(JOB)
-         .where(JOB.state == job::job_state::Running).compile(c->dialect())
+         .where(JOB.state == job::job_state::Running)
       ) &&
-      in(PAYLOAD.id, query::select({TEMPORARY_TABLE.id})
+      in(PAYLOAD.id, select({TEMPORARY_TABLE.id})
-         .from(TEMPORARY_TABLE).compile(c->dialect())
+         .from(TEMPORARY_TABLE)
       )
     ).compile(c->dialect());
   // // .fetch_value<unsigned long>();

demo/object.cpp

@@ -29,7 +29,7 @@ public:
   attribute() = default;
   attribute(std::string name,
             utils::basic_type type,
-            const utils::field_attributes& opts = utils::null_attributes,
+            const utils::field_attributes& opts = matador::NullAttributes,
             null_option_type null_opt = null_option_type::NotNull)
   : name_(std::move(name)), type_(type), options_(opts), null_option_type_(null_opt) {}
 

demo/recipe.hpp

@@ -13,8 +13,7 @@
 namespace demo {
 
 struct recipe;
-struct ingredient
+struct ingredient {
-{
   unsigned int id{};
   std::string name;
   matador::object::collection<matador::object::object_ptr<demo::recipe>> recipes{};
@@ -25,15 +24,15 @@ struct ingredient
 
   template<class Operator>
   void process(Operator &op) {
-    namespace field = matador::access;
+    using namespace matador;
+    namespace field = access;
     field::primary_key(op, "id", id);
-    field::attribute(op, "name", name, 255);
+    field::attribute(op, "name", name, VarChar255);
-    field::has_many_to_many(op, "recipe_ingredients", recipes, "ingredient_id", "recipe_id", matador::utils::fetch_type::Eager);
+    field::has_many_to_many(op, "recipe_ingredients", recipes, "ingredient_id", "recipe_id", utils::CascadeAllFetchEager);
   }
 };
 
-struct recipe
+struct recipe {
-{
   unsigned int id{};
   std::string name;
   matador::object::collection<matador::object::object_ptr<demo::ingredient>> ingredients{};
@@ -44,10 +43,11 @@ struct recipe
 
   template<class Operator>
   void process(Operator &op) {
-    namespace field = matador::access;
+    using namespace matador;
+    namespace field = access;
     field::primary_key(op, "id", id);
-    field::attribute(op, "name", name, 255);
+    field::attribute(op, "name", name, VarChar255);
-    field::has_many_to_many(op, "recipe_ingredients", ingredients, matador::utils::fetch_type::Lazy);
+    field::has_many_to_many(op, "recipe_ingredients", ingredients, utils::CascadeAllFetchLazy);
   }
 };
 

demo/sandbox.cpp

@@ -81,11 +81,12 @@ struct profile {
 
     template<typename Operator>
     void process(Operator &op) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::primary_key( op, "id", id );
-        field::attribute( op, "first_name", first_name, 255 );
+        field::attribute( op, "first_name", first_name, VarChar255 );
-        field::attribute( op, "last_name", last_name, 255 );
+        field::attribute( op, "last_name", last_name, VarChar255 );
-        field::belongs_to( op, "user_id", user, matador::utils::CascadeNoneFetchLazy );
+        field::belongs_to( op, "user_id", user, utils::CascadeNoneFetchLazy );
     }
 };
 struct user {
@@ -95,10 +96,11 @@ struct user {
 
     template<typename Operator>
     void process(Operator &op) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::primary_key( op, "id", id );
-        field::attribute( op, "username", username, 255 );
+        field::attribute( op, "username", username, VarChar255 );
-        field::has_one(op, "profile_id", profile, matador::utils::CascadeNoneFetchLazy );
+        field::has_one(op, "profiles", profile, "profile_id", utils::CascadeNoneFetchLazy );
     }
 };
 
@@ -108,9 +110,10 @@ struct person {
 
     template<typename Operator>
     void process(Operator &op) {
+        using namespace matador;
         namespace field = matador::access;
         field::primary_key( op, "id", id );
-        field::attribute( op, "name", name, 255 );
+        field::attribute( op, "name", name, VarChar255 );
     }
 };
 
@@ -136,7 +139,7 @@ int main() {
 
   sql::resolver_service rs;
 
-  std::weak_ptr cr = rs.collection_resolver<object::object_ptr<names>>( typeid(person), "names" );
+  std::weak_ptr cr = rs.joined_collection_resolver<object::object_ptr<names>>( typeid(person), "names" );
   utils::identifier id{1};
 
   object::collection_proxy cp(cr, id);

demo/work.cpp

@@ -23,7 +23,7 @@
 
 #include "matador/query/schema.hpp"
 
-#include "matador/orm/session.hpp"
+#include "matador/query/session.hpp"
 
 template <> struct matador::utils::data_type_traits<work::core::UserInfo, void> {
     static basic_type type(std::size_t /*size*/) { return basic_type::UInt64; }
@@ -88,6 +88,7 @@ int main() {
         .and_then([&admin_schema] { return admin_schema.attach<jobs::IdPayload, jobs::Payload>("id_list_payloads"); })
         .and_then([&admin_schema] { return admin_schema.attach<jobs::IdListPayload, jobs::Payload>("id_payloads"); })
         .and_then([&admin_schema] { return admin_schema.attach<jobs::Task>("tasks"); })
+        .and_then([&admin_schema, &pool] { return admin_schema.create( *pool.acquire() ); })
     ;
     admin_schema.dump(std::cout);
 
@@ -109,7 +110,7 @@ int main() {
     // }
 
 /*
-  *        const auto statement = QString( "SELECT %5.%6, %1.%2 FROM %3 %1, %4 %5 WHERE %1.%2=%5.%6 AND %7" )
+const auto statement = QString( "SELECT %5.%6, %1.%2 FROM %3 %1, %4 %5 WHERE %1.%2=%5.%6 AND %7" )
   .arg( payloadTableAliasName,
   payloadSqlMetaInfo.columnName( Payload::Attributes::idAttributeId() ),
   Payload::staticSqlMetaInfo().tableName(),
@@ -125,7 +126,7 @@ int main() {
   const auto payloads = PAYLOAD.as( "payloads" );
   const auto tasks = TASK.as( "tasks" );
 
-  const auto stmt1 = query:: query::select( { tasks.payload, payloads.id } )
+  const auto stmt1 = query::select( { tasks.payload, payloads.id } )
     .from( tasks, payloads )
     .where ( payloads.id == tasks.payload )
     .str( conn->dialect() );
@@ -158,12 +159,12 @@ int main() {
   const auto iPT = ID_PAYLOAD.as("iPT");
   const auto pT = PAYLOAD.as("pT");
 
-  const auto stmt2 = query::query::select({ iPT.payload_id })
+  const auto stmt2 = query::select({ iPT.payload_id })
     .from( iPT )
     .join_left( pT ).on( iPT.id == pT.id )
     .where(
-      in( pT.id, query::query::select({ JOB.payload }).from( JOB ).where( JOB.state == _) ) &&
+      in( pT.id, query::select({ JOB.payload }).from( JOB ).where( JOB.state == _) ) &&
-      in( iPT.payload_id, query::query::select({ temp_id_col }).from( temporary ) )
+      in( iPT.payload_id, query::select({ temp_id_col }).from( temporary ) )
     )
   .str( conn->dialect() );
 
@@ -177,13 +178,13 @@ int main() {
       //                         .arg( LoginHistory::staticSqlMetaInfo().columnName( LoginHistory::Attributes::failReasonSqlAttributeId() ) )
       //                         .arg( LoginHistory::staticSqlMetaInfo().columnName( LoginHistory::Attributes::idAttributeId() ) );
 
-  const auto q = query::query::select({LOGIN_HISTORY.client, query::maximum(LOGIN_HISTORY.login_time).as( "lastSuccessfulLogin" ) } )
+  const auto q = query::select({LOGIN_HISTORY.client, query::maximum(LOGIN_HISTORY.login_time).as( "lastSuccessfulLogin" ) } )
     .from( LOGIN_HISTORY )
     .where( LOGIN_HISTORY.fail_reason == _ )
     .group_by( LOGIN_HISTORY.client );
     // .as_table("ll");
 
-  const auto stmt3 = query::query::select({ LOGIN_HISTORY.client })
+  const auto stmt3 = query::select({ LOGIN_HISTORY.client })
     .from( LOGIN_HISTORY )
     .join_left(q/*, "ll"*/ )
     .on( LOGIN_HISTORY.client == "ll.client" )
@@ -287,11 +288,11 @@ int main() {
   //     )
   //   )
 
-  const auto stmt4 = query::query::select({JOB.id})
+  const auto stmt4 = query::select({JOB.id})
     .from(JOB)
-    .where( JOB.id > _ && JOB.name == _ && in( JOB.payload, query::query::select({PAYLOAD.id}).from(PAYLOAD).where(
+    .where( JOB.id > _ && JOB.name == _ && in( JOB.payload, query::select({PAYLOAD.id}).from(PAYLOAD).where(
-    in( PAYLOAD.id, query::query::select({ID_PAYLOAD.id}).from(ID_PAYLOAD).where(
+    in( PAYLOAD.id, query::select({ID_PAYLOAD.id}).from(ID_PAYLOAD).where(
-      in( ID_PAYLOAD.id, query::query::select({temp_id_col}).from(temporary))
+      in( ID_PAYLOAD.id, query::select({temp_id_col}).from(temporary))
     ) ) ) ) )
     .str( conn->dialect() );
 
@@ -306,7 +307,7 @@ int main() {
 // WHERE nj.ID > ?
 //   AND nj.TYPE = ?;
 
-  const auto stmt5 = query::query::select({JOB.id})
+  const auto stmt5 = query::select({JOB.id})
     .from(JOB)
     .join_left(PAYLOAD).on(JOB.payload == PAYLOAD.id)
     .join_left(ID_PAYLOAD).on(PAYLOAD.id == ID_PAYLOAD.id)

demo/work/admin/CollectionCenter.hpp

@@ -36,12 +36,13 @@ struct CollectionCenter : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
+        using namespace matador;
         namespace field = matador::access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::attribute( op, "name", name, 511 );
+        field::attribute( op, "name", name, UniqueVarChar511 );
         field::attribute( op, "symbol", symbol );
         field::attribute( op, "type", type );
-        field::has_many( op, "collection_center_users", users, "users_id", matador::utils::fetch_type::Lazy );
+        field::has_many( op, "collection_center_users", users, "users_id", utils::CascadeAllFetchLazy );
     }
 };
 

demo/work/admin/InternalUserDirectory.hpp

@@ -15,4 +15,4 @@ struct InternalUserDirectory : UserDirectory {
 };
 }
 
-#endif //INTERNALUSERDIRECTORY_HPP
+#endif //INTERNAL_USER_DIRECTORY_HPP

demo/work/admin/LdapGroupSchemaSettings.hpp

@@ -16,11 +16,12 @@ struct LdapGroupSchemaSettings : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::has_one(op, "ldap_user_directory", ldap_user_directory, matador::utils::CascadeAllFetchLazy);
+        field::has_one(op, "ldap_user_directory", ldap_user_directory, utils::CascadeAllFetchLazy);
-        field::attribute( op, "group_object_filter", group_object_filter, 511 );
+        field::attribute( op, "group_object_filter", group_object_filter, VarChar511 );
-        field::attribute( op, "user_member_attribute", user_member_attribute, 511 );
+        field::attribute( op, "user_member_attribute", user_member_attribute, VarChar511 );
     }
 };
 

demo/work/admin/LdapImportSettings.hpp

@@ -17,10 +17,11 @@ struct LdapImportSettings : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::has_one(op, "ldap_user_directory", ldap_user_directory, matador::utils::CascadeAllFetchLazy);
+        field::has_one(op, "ldap_user_directory", ldap_user_directory, utils::CascadeAllFetchLazy);
-        field::attribute( op, "default_role", default_role, 511 );
+        field::attribute( op, "default_role", default_role, VarChar511 );
         field::attribute( op, "sync_interval", sync_interval );
         field::attribute( op, "network_timeout", network_timeout );
     }

demo/work/admin/LdapUserDirectory.hpp

@@ -25,16 +25,17 @@ struct LdapUserDirectory : UserDirectory {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::process( op, *matador::base_class<UserDirectory>( this ) );
-        field::attribute( op, "schema_base_dn", schema_base_dn, 511 );
+        field::attribute( op, "schema_base_dn", schema_base_dn, VarChar511 );
-        field::attribute( op, "additional_user_base_dn", additional_user_base_dn, 511 );
+        field::attribute( op, "additional_user_base_dn", additional_user_base_dn, VarChar511 );
-        field::attribute( op, "additional_group_base_dn", additional_group_base_dn, 511 );
+        field::attribute( op, "additional_group_base_dn", additional_group_base_dn, VarChar511 );
-        field::belongs_to( op, "user_schema_settings", user_schema_settings, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "user_schema_settings", user_schema_settings, utils::CascadeAllFetchLazy );
-        field::belongs_to( op, "group_schema_settings", group_schema_settings, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "group_schema_settings", group_schema_settings, utils::CascadeAllFetchLazy );
-        field::belongs_to( op, "import_settings", import_settings, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "import_settings", import_settings, utils::CascadeAllFetchLazy );
-        field::has_many( op, "ldap_users", users, "users_id", matador::utils::CascadeAllFetchEager );
+        field::has_many( op, "ldap_users", users, "users_id", utils::CascadeAllFetchEager );
-        field::has_many( op, "ldap_groups", groups, "groups_id", matador::utils::CascadeAllFetchEager );
+        field::has_many( op, "ldap_groups", groups, "groups_id", utils::CascadeAllFetchEager );
     }
 };
 }

demo/work/admin/LdapUserSchemaSettings.hpp

@@ -18,13 +18,14 @@ struct LdapUserSchemaSettings : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::process(op, *matador::base_class<Model>( this ));
-        field::has_one(op, "ldap_user_directory", ldap_user_directory, matador::utils::CascadeAllFetchLazy);
+        field::has_one(op, "ldap_user_directory", ldap_user_directory, utils::CascadeAllFetchLazy);
-        field::attribute(op, "user_object_filter", user_object_filter, 511);
+        field::attribute(op, "user_object_filter", user_object_filter, VarChar511);
-        field::attribute(op, "user_unique_id_attribute", user_unique_id_attribute, 511);
+        field::attribute(op, "user_unique_id_attribute", user_unique_id_attribute, VarChar511);
-        field::attribute(op, "user_member_of_attribute", user_member_of_attribute, 511);
+        field::attribute(op, "user_member_of_attribute", user_member_of_attribute, VarChar511);
-        field::attribute(op, "user_name_attribute", user_name_attribute, 511);
+        field::attribute(op, "user_name_attribute", user_name_attribute, VarChar511);
     }
 };
 

demo/work/admin/LoginHistory.hpp

@@ -51,12 +51,14 @@ struct LoginHistory : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
+        field::process_base<Model>( op, *this );
         field::process( op, *matador::base_class<Model>( this ) );
-        field::belongs_to( op, "client", client, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "client", client, utils::CascadeAllFetchLazy );
-        field::belongs_to( op, "scenario", scenario, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "scenario", scenario, utils::CascadeAllFetchLazy );
-        field::belongs_to( op, "collection_center", collection_center, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "collection_center", collection_center, utils::CascadeAllFetchLazy );
-        field::attribute( op, "login_name", login_name, 511 );
+        field::attribute( op, "login_name", login_name, VarChar511 );
         field::attribute( op, "fail_reason", fail_reason );
         field::attribute( op, "login_time", login_time );
     }

demo/work/admin/Scenario.hpp

@@ -46,14 +46,15 @@ struct Scenario : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::attribute( op, "name", name, 511 );
+        field::attribute( op, "name", name, UniqueVarChar511 );
         field::attribute( op, "mode", mode );
-        field::attribute( op, "description", description, 511 );
+        field::attribute( op, "description", description, VarChar511 );
         field::attribute( op, "symbol", symbol );
         field::attribute( op, "state", state );
-        field::has_many( op, "collection_center", collection_center, "scenario_id", matador::utils::fetch_type::Lazy );
+        field::has_many( op, "collection_center", collection_center, "scenario_id", utils::CascadeAllFetchLazy );
     }
 };
 }

demo/work/admin/User.hpp

@@ -29,17 +29,18 @@ struct User : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::attribute( op, "name", name, 511 );
+        field::attribute( op, "name", name, UniqueVarChar511 );
         field::attribute( op, "symbol", symbol );
-        field::attribute( op, "salt", salt, 511 );
+        field::attribute( op, "salt", salt, VarChar511 );
-        field::attribute( op, "password", password, 511 );
+        field::attribute( op, "password", password, VarChar511 );
         field::attribute( op, "lock_type", lock_type );
         field::attribute( op, "locked_at", locked_at );
-        field::attribute( op, "lock_reason", lock_reason, 511 );
+        field::attribute( op, "lock_reason", lock_reason, VarChar511 );
-        field::attribute( op, "role", role, 63 );
+        field::attribute( op, "role", role, VarChar63 );
-        field::belongs_to( op, "user_directory", user_directory, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "user_directory", user_directory, utils::CascadeAllFetchLazy );
     }
 };
 

demo/work/admin/UserDirectory.hpp

@@ -13,7 +13,7 @@ struct UserDirectory : core::Model {
     void process( Operator& op ) {
         namespace field = matador::access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::attribute( op, "name", name, 511 );
+        field::attribute( op, "name", name, matador::VarChar511 );
     }
 };
 }

demo/work/admin/UserSession.hpp

@@ -21,11 +21,12 @@ struct UserSession : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
-        namespace field = matador::access;
+        using namespace matador;
+        namespace field = access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::belongs_to( op, "client", client, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "client", client, utils::CascadeAllFetchLazy );
-        field::belongs_to( op, "scenario", scenario, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "scenario", scenario, utils::CascadeAllFetchLazy );
-        field::belongs_to( op, "collection_center", collection_center, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "collection_center", collection_center, utils::CascadeAllFetchLazy );
         field::attribute( op, "offline_since", offline_since );
     }
 };

demo/work/core/UserInfo.hpp

@@ -2,6 +2,7 @@
 #define USERINFO_HPP
 
 #include "matador/utils/access.hpp"
+#include "matador/utils/field_attributes.hpp"
 
 namespace work::core {
 struct UserInfo {
@@ -12,9 +13,10 @@ struct UserInfo {
     template<typename Operator>
     void process( Operator& op ) {
         namespace field = matador::access;
+        using namespace matador;
         field::attribute( op, "user_session_id", user_session_id );
-        field::attribute( op, "user_role", user_role, 255 );
+        field::attribute( op, "user_role", user_role, VarChar255 );
-        field::attribute( op, "database_name", database_name, 255 );
+        field::attribute( op, "database_name", database_name, VarChar255 );
     }
 };
 }

demo/work/jobs/Job.hpp

@@ -30,15 +30,16 @@ struct Job : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
+        using namespace matador;
         namespace field = matador::access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::attribute( op, "name", name, 511 );
+        field::attribute( op, "name", name, UniqueVarChar511 );
-        field::attribute( op, "description", description, 511 );
+        field::attribute( op, "description", description, VarChar1023 );
         field::attribute( op, "state", state );
         field::attribute( op, "mode", mode );
         field::attribute( op, "created_at", created_at );
-        field::has_one(op, "payload", payload, matador::utils::CascadeAllFetchLazy );
+        field::has_one(op, "payload", payload, utils::CascadeAllFetchLazy );
-        field::belongs_to( op, "task", task, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "task", task, utils::CascadeAllFetchLazy );
         field::attribute( op, "user_info", user_info );
     }
 };

demo/work/jobs/Payload.hpp

@@ -16,10 +16,11 @@ struct Payload : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
+        using namespace matador;
         namespace field = matador::access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::attribute( op, "type", type, 255 );
+        field::attribute( op, "type", type, VarChar255 );
-        field::belongs_to( op, "job", job, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "job", job, utils::CascadeAllFetchLazy );
     }
 };
 }

demo/work/jobs/Task.hpp

@@ -26,13 +26,14 @@ struct Task : core::Model {
 
     template<typename Operator>
     void process( Operator& op ) {
+        using namespace matador;
         namespace field = matador::access;
         field::process( op, *matador::base_class<Model>( this ) );
-        field::attribute( op, "name", name, 511 );
+        field::attribute( op, "name", name, UniqueVarChar511 );
-        field::attribute( op, "description", description, 511 );
+        field::attribute( op, "description", description, VarChar1023 );
-        field::attribute( op, "job_name", job_name, 511 );
+        field::attribute( op, "job_name", job_name, VarChar511 );
         field::attribute( op, "state", state );
-        field::belongs_to( op, "payload", payload, matador::utils::CascadeAllFetchLazy );
+        field::belongs_to( op, "payload", payload, utils::CascadeAllFetchLazy );
         field::attribute( op, "job_mode", job_mode );
         field::attribute( op, "start_delay", start_delay );
         field::attribute( op, "interval", interval );

include/matador/object/abstract_joined_resolver.hpp

@@ -1,24 +1,22 @@
 #ifndef MATADOR_ABSTRACT_COLLECTION_RESOLVER_HPP
 #define MATADOR_ABSTRACT_COLLECTION_RESOLVER_HPP
 
+#include "matador/object/abstract_type_resolver.hpp"
+
 #include <string>
 #include <typeindex>
 
 namespace matador::object {
-class abstract_collection_resolver {
+class abstract_joined_resolver : public abstract_type_resolver {
 public:
-  virtual ~abstract_collection_resolver() = default;
-
   [[nodiscard]] const std::type_index& root_type() const;
-  [[nodiscard]] const std::type_index& type() const;
   [[nodiscard]] const std::string& collection_name() const;
 
- protected:
+protected:
-  explicit abstract_collection_resolver(const std::type_index& root_type, const std::type_index& type, std::string collection_name);
+  explicit abstract_joined_resolver(const std::type_index& root_type, const std::type_index& type, std::string collection_name);
 
 public:
   const std::type_index root_type_;
-  const std::type_index type_;
   const std::string collection_name_;
 };
 }

include/matador/object/attribute.hpp

@@ -28,20 +28,21 @@ public:
   attribute() = default;
   attribute(std::string name,
             utils::basic_type type,
-            const utils::field_attributes &attr = utils::null_attributes,
+            const utils::field_attributes &attr = NullAttributes,
             null_option_type null_opt = null_option_type::NotNull);
 
   [[nodiscard]] const std::string& name() const;
   void name(const std::string& n);
   [[nodiscard]] std::string full_name() const;
+  [[nodiscard]] size_t index() const;
   [[nodiscard]] const utils::field_attributes& attributes() const;
   [[nodiscard]] utils::field_attributes& attributes();
   [[nodiscard]] bool is_nullable() const;
   [[nodiscard]] utils::basic_type type() const;
   [[nodiscard]] std::shared_ptr<object> owner() const;
-  void change_type(utils::basic_type type, const utils::field_attributes &attr = utils::null_attributes);
+  void change_type(utils::basic_type type, const utils::field_attributes &attr = NullAttributes);
   template < typename Type >
-  void change_type(const utils::field_attributes &attr = utils::null_attributes) {
+  void change_type(const utils::field_attributes &attr = NullAttributes) {
       type_ = utils::data_type_traits<Type>::type(attr.size());
   }
 
@@ -68,6 +69,7 @@ private:
   friend class object_generator;
 
   std::string name_;
+  size_t index_{0};
   std::weak_ptr<object> owner_;
   utils::basic_type type_{utils::basic_type::Null};
   utils::field_attributes options_{};

include/matador/object/basic_object_info.hpp

@@ -27,12 +27,12 @@ public:
   [[nodiscard]] std::type_index type_index() const;
   [[nodiscard]] std::string name() const;
   [[nodiscard]] std::shared_ptr<class object> object() const;
-  [[nodiscard]] const std::list<attribute>& attributes() const;
+  [[nodiscard]] const std::vector<attribute>& attributes() const;
-  [[nodiscard]] const std::list<class restriction>& constraints() const;
+  [[nodiscard]] const std::list<restriction>& constraints() const;
 
   [[nodiscard]] bool has_primary_key() const;
   [[nodiscard]] const utils::identifier& primary_key() const;
-  [[nodiscard]]  attribute* primary_key_attribute() const;
+  [[nodiscard]] const attribute* primary_key_attribute() const;
 
   void update_name(const std::string& name) const;
 

include/matador/object/basic_repository.hpp

@@ -95,7 +95,7 @@ public:
     return basic_info(std::type_index(typeid(Type)));
   }
 
-  [[nodiscard]] utils::result<attribute*, utils::error> primary_key_attribute(const std::type_index &ti) const;
+  [[nodiscard]] utils::result<const attribute*, utils::error> primary_key_attribute(const std::type_index &ti) const;
 
   void dump(std::ostream &os) const;
   static void dump(std::ostream &os, const repository_node& node);

include/matador/object/collection.hpp

@@ -8,9 +8,9 @@ namespace matador::object {
 template < class Type >
 class collection {
 public:
-  using value_type = Type;
+  using value_type = typename collection_proxy<Type>::value_type;
-  using iterator = typename std::vector<value_type>::iterator;
+  using iterator = typename collection_proxy<Type>::iterator;
-  using const_iterator = typename std::vector<value_type>::const_iterator;
+  using const_iterator = typename collection_proxy<Type>::const_iterator;
 
   collection()
   : proxy_(std::make_shared<collection_proxy<Type>>()) {}
@@ -21,31 +21,31 @@ public:
   collection(const collection& other) = default;
 
   void push_back(const value_type& value) {
-    proxy_->items().push_back(value);
+    proxy_->push_back(value);
   }
 
   iterator begin() {
-    return proxy_->items().begin();
+    return proxy_->begin();
   }
 
   iterator end() {
-    return proxy_->items().end();
+    return proxy_->end();
   }
 
   const_iterator begin() const {
-    return proxy_->items().begin();
+    return proxy_->begin();
   }
 
   const_iterator end() const {
-    return proxy_->items().end();
+    return proxy_->end();
   }
 
   [[nodiscard]] size_t size() const {
-    return proxy_->items().size();
+    return proxy_->size();
   }
 
   [[nodiscard]] bool empty() const {
-    return proxy_->items().empty();
+    return proxy_->empty();
   }
 
   void reset(std::shared_ptr<collection_proxy<Type>> proxy) {
@@ -53,7 +53,7 @@ public:
   }
 
 private:
-  std::shared_ptr<collection_proxy<Type>> proxy_;
+  std::shared_ptr<abstract_collection_proxy<Type>> proxy_;
 };
 
 }

include/matador/object/collection_proxy.hpp

@@ -1,8 +1,8 @@
 #ifndef MATADOR_COLLECTION_PROXY_HPP
 #define MATADOR_COLLECTION_PROXY_HPP
 
-
 #include "matador/object/collection_resolver.hpp"
+#include "matador/object/many_to_many_relation.hpp"
 
 #include "matador/utils/identifier.hpp"
 
@@ -12,10 +12,100 @@
 
 namespace matador::object {
 
+// has many primitive
+// relation<OwnerType, PrimitiveType>
+// has many ptr
+// relation<OwnerType, ObjectType>
+// has many to many
+// relation<OwnerType, ForeignType>
+
+template < class RelationType >
+struct relation_iterator_traits {
+  static RelationType& value(RelationType& item) {
+    return item;
+  }
+};
+
+template < typename Type, typename OwnerType >
+struct relation_iterator_traits<relation<OwnerType, Type>> {
+  static Type& value(relation<OwnerType, Type>& re) {
+    return re.relation().value();
+  }
+};
+
+template<typename Type, typename RelationType = Type>
+class collection_proxy_iterator {
+public:
+  using value_type = Type;
+  using reference = Type&;
+  using pointer = Type*;
+  using relation_type = RelationType;
+  using iterator_category = std::forward_iterator_tag;
+
+  collection_proxy_iterator() = default;
+  collection_proxy_iterator(typename std::vector<RelationType>::iterator it)
+  : it_(it) {}
+
+  reference operator*() {
+    return relation_iterator_traits<relation_type>::value(*it_);
+  }
+
+  pointer operator->() {
+    return &relation_iterator_traits<relation_type>::value(*it_);
+  }
+
+  collection_proxy_iterator& operator++() {
+    ++it_;
+    return *this;
+  }
+  bool operator==(const collection_proxy_iterator& other) const {
+    return it_ == other.it_;
+  }
+  bool operator!=(const collection_proxy_iterator& other) const {
+    return !operator==(other);
+  }
+
+  // relation_type& relation() {
+
+    // return *it_;
+  // }
+private:
+  typename std::vector<RelationType>::iterator it_;
+};
+
+template<typename Type, typename RelationType = Type>
+class abstract_collection_proxy {
+public:
+  using value_type = Type;
+  using relation_type = RelationType;
+  // using iterator = typename std::vector<value_type>::iterator;
+  // using const_iterator = typename std::vector<value_type>::const_iterator;
+  using iterator = collection_proxy_iterator<value_type, relation_type>;
+  using const_iterator = collection_proxy_iterator<value_type, relation_type>;
+
+  virtual ~abstract_collection_proxy() = default;
+
+  virtual void push_back(const value_type& value) = 0;
+
+  virtual iterator begin() = 0;
+  virtual iterator end() = 0;
+
+  [[nodiscard]] virtual size_t size() = 0;
+  [[nodiscard]] virtual bool empty() = 0;
+
+  [[nodiscard]] virtual const utils::identifier& owner_id() const = 0;
+
+protected:
+  std::vector<relation_type> items_;
+};
 
 template<typename Type>
-class collection_proxy final {
+class collection_proxy : public abstract_collection_proxy<Type> {
 public:
+  using value_type = Type;
+  using iterator = typename abstract_collection_proxy<Type>::iterator;
+  using const_iterator = typename abstract_collection_proxy<Type>::const_iterator;
+
   collection_proxy() = default;
 
   // Lazy
@@ -30,17 +120,32 @@ public:
   explicit collection_proxy(std::vector<Type> items)
   : items_(std::move(items)) {}
 
-  [[nodiscard]] const utils::identifier& owner_id() const {
+  [[nodiscard]] const utils::identifier& owner_id() const override {
     return owner_id_;
   }
-  const std::vector<Type>& items() const {
+
+  iterator begin() override {
     resolve();
-    return items_;
+    return items_.begin();
   }
-  std::vector<Type>& items() {
+  iterator end() override {
     resolve();
-    return items_;
+    return items_.end();
   }
+
+  void push_back(const value_type& value) override {
+    resolve();
+    items_.push_back(value);
+  }
+  [[nodiscard]] size_t size() override {
+    resolve();
+    return items_.size();
+  }
+  [[nodiscard]] bool empty() override {
+    resolve();
+    return items_.empty();
+  }
+
 private:
   void resolve() {
     if (loaded_) {
@@ -66,5 +171,18 @@ private:
   std::weak_ptr<collection_resolver<Type>> resolver_{};
   mutable std::mutex mutex_{};
 };
+
+template<typename Type, class OwnerType>
+class collection_many_to_many_proxy {
+public:
+  using value_type = Type;
+  using owner_type = OwnerType;
+  using relation_type = many_to_many_relation<value_type, owner_type>;
+  using iterator = typename std::vector<relation_type>::iterator;
+  using const_iterator = typename std::vector<relation_type>::const_iterator;
+
+private:
+  std::vector<relation_type> relations_;
+};
 }
 #endif //MATADOR_COLLECTION_PROXY_HPP

include/matador/object/collection_resolver.hpp

@@ -1,7 +1,7 @@
 #ifndef MATADOR_COLLECTION_RESOLVER_HPP
 #define MATADOR_COLLECTION_RESOLVER_HPP
 
-#include "matador/object/abstract_collection_resolver.hpp"
+#include "matador/object/abstract_joined_resolver.hpp"
 
 #include <typeindex>
 #include <vector>
@@ -12,10 +12,10 @@ class identifier;
 
 namespace matador::object {
 template<typename Type>
-class collection_resolver : public abstract_collection_resolver {
+class collection_resolver : public abstract_joined_resolver {
 public:
   collection_resolver(const std::type_index& root_type, std::string collection_name)
-  : abstract_collection_resolver(root_type, typeid(Type), std::move(collection_name)) {}
+  : abstract_joined_resolver(root_type, typeid(Type), std::move(collection_name)) {}
 
   virtual std::vector<Type> resolve(const utils::identifier& id) = 0;
 };

include/matador/object/collection_resolver_factory.hpp

@@ -1,28 +0,0 @@
-#ifndef MATADOR_CONTAINER_RESOLVER_FACTORY_HPP
-#define MATADOR_CONTAINER_RESOLVER_FACTORY_HPP
-
-#include "matador/object/collection_resolver.hpp"
-
-namespace matador::object {
-class abstract_collection_resolver_factory {
-public:
-  virtual ~abstract_collection_resolver_factory() = default;
-
-  [[nodiscard]] virtual std::shared_ptr<abstract_collection_resolver> acquire_collection_resolver(const std::type_index &root_type, const std::type_index &element_type, const std::string &collection_name) const = 0;
-  virtual void register_collection_resolver(std::shared_ptr<abstract_collection_resolver> &&resolver) = 0;
-};
-
-class collection_resolver_factory : public abstract_collection_resolver_factory {
-public:
-  template<class Type>
-  [[nodiscard]] std::shared_ptr<collection_resolver<Type>> resolver(const std::type_index &root_type, const std::string &collection_name) const {
-    const auto res = acquire_collection_resolver(root_type, typeid(Type), collection_name);
-    if (!res) {
-      return std::dynamic_pointer_cast<collection_resolver<Type>>(res);
-    }
-
-    return std::dynamic_pointer_cast<collection_resolver<Type>>(res);
-  }
-};
-}
-#endif //MATADOR_CONTAINER_RESOLVER_FACTORY_HPP

include/matador/object/foreign_node_completer.hpp

@@ -38,17 +38,19 @@ public:
     completer.complete_node(node);
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template<class PrimaryKeyType>
-  static void on_primary_key(const char * /*id*/, PrimaryKeyType &/*pk*/, const utils::primary_key_attribute & /*attr*/ = utils::default_pk_attributes) {}
+  static void on_primary_key(const char * /*id*/, PrimaryKeyType &/*pk*/, const utils::primary_key_attribute & /*attr*/) {}
   static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
   template<typename AttributeType>
-  static void on_attribute(const char * /*id*/, AttributeType &/*val*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, AttributeType &/*val*/, const utils::field_attributes &/*attr*/) {}
   template<typename AttributeType>
-  static void on_attribute(const char * /*id*/, std::optional<AttributeType> &/*val*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, std::optional<AttributeType> &/*val*/, const utils::field_attributes &/*attr*/) {}
   template<class ForeignPointerType>
   void on_belongs_to(const char *id, ForeignPointerType &/*obj*/, const utils::foreign_attributes &/*attr*/);
   template<class ForeignPointerType>
-  void on_has_one(const char * /*id*/, ForeignPointerType &/*obj*/, const utils::foreign_attributes &/*attr*/);
+  void on_has_one(const char * /*id*/, ForeignPointerType &/*obj*/, const char *join_column, const utils::foreign_attributes &/*attr*/);
   template<class CollectionType>
   void on_has_many(const char *id, CollectionType &,
                    const char *join_column,
@@ -132,7 +134,7 @@ void foreign_node_completer<NodeType, Observers...>::on_belongs_to(const char *
 
 template<typename NodeType, template<typename> typename ...Observers>
 template<class ForeignPointerType>
-void foreign_node_completer<NodeType, Observers...>::on_has_one(const char * /*id*/, ForeignPointerType &, const utils::foreign_attributes &) {
+void foreign_node_completer<NodeType, Observers...>::on_has_one(const char * /*id*/, ForeignPointerType &, const char * /*join_column*/, const utils::foreign_attributes &) {
   attach_node<typename ForeignPointerType::value_type>();
 }
 

include/matador/object/join_columns_collector.hpp

@@ -24,15 +24,17 @@ public:
 
         return join_columns_;
     }
+    template<typename BaseType>
+    static void on_base(const BaseType&) {}
     template < class V >
-    static void on_primary_key(const char * /*id*/, V &, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {}
+    static void on_primary_key(const char * /*id*/, V &, const utils::primary_key_attribute& /*attr*/) {}
     static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
     template<typename Type>
-    static void on_attribute(const char * /*id*/, Type &, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+    static void on_attribute(const char * /*id*/, Type &, const utils::field_attributes &/*attr*/) {}
     template<class Pointer>
     static void on_belongs_to(const char * /*id*/, Pointer &/*obj*/, const utils::foreign_attributes &/*attr*/) {}
     template<class Pointer>
-    static void on_has_one(const char * /*id*/, Pointer &/*obj*/, const utils::foreign_attributes &/*attr*/) {}
+    static void on_has_one(const char * /*id*/, Pointer &/*obj*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {}
     template<class ContainerType>
     static void on_has_many(ContainerType &, const char */*join_column*/, const utils::foreign_attributes &/*attr*/) {}
     template<class ContainerType>

include/matador/object/joined_collection_resolver_factory.hpp

@@ -0,0 +1,51 @@
+#ifndef MATADOR_CONTAINER_RESOLVER_FACTORY_HPP
+#define MATADOR_CONTAINER_RESOLVER_FACTORY_HPP
+
+#include "matador/object/collection_resolver.hpp"
+
+#include <memory>
+
+namespace matador::object {
+class abstract_collection_resolver_factory {
+public:
+  virtual ~abstract_collection_resolver_factory() = default;
+
+  [[nodiscard]] virtual std::shared_ptr<abstract_joined_resolver> acquire_collection_resolver(const std::type_index &root_type, const std::type_index &element_type, const std::string &collection_name) const = 0;
+  virtual void register_collection_resolver(std::shared_ptr<abstract_joined_resolver> &&resolver) = 0;
+};
+
+class joined_collection_resolver_factory : public abstract_collection_resolver_factory {
+public:
+  template<class Type>
+  [[nodiscard]] std::shared_ptr<collection_resolver<Type>> resolver(const std::type_index &root_type, const std::string &collection_name) const {
+    const auto res = acquire_collection_resolver(root_type, typeid(Type), collection_name);
+    if (!res) {
+      return std::dynamic_pointer_cast<collection_resolver<Type>>(res);
+    }
+
+    return std::dynamic_pointer_cast<collection_resolver<Type>>(res);
+  }
+};
+
+class abstract_joined_object_resolver_factory {
+public:
+  virtual ~abstract_joined_object_resolver_factory() = default;
+
+  [[nodiscard]] virtual std::shared_ptr<abstract_type_resolver> acquire_joined_object_resolver(const std::type_index &root_type, const std::type_index &element_type, const std::string &collection_name) const = 0;
+  virtual void register_joined_object_resolver(std::shared_ptr<abstract_type_resolver> &&resolver, const std::type_index& root_type, const std::string& join_column) = 0;
+};
+
+class joined_object_resolver_factory : public abstract_joined_object_resolver_factory {
+public:
+  template<class Type>
+  [[nodiscard]] std::shared_ptr<object_resolver<Type>> resolver(const std::type_index &root_type, const std::string &collection_name) const {
+    const auto res = acquire_joined_object_resolver(root_type, typeid(Type), collection_name);
+    if (!res) {
+      return std::dynamic_pointer_cast<object_resolver<Type>>(res);
+    }
+
+    return std::dynamic_pointer_cast<object_resolver<Type>>(res);
+  }
+};
+}
+#endif //MATADOR_CONTAINER_RESOLVER_FACTORY_HPP

include/matador/object/many_to_many_relation.hpp

@@ -8,6 +8,48 @@
 
 namespace matador::object {
 
+template < class LocalType, class ForeignType >
+class relation {
+public:
+    relation() = default;
+    relation(std::string local_name, std::string remote_name)
+    : local_name_(std::move(local_name))
+    , remote_name_(std::move(remote_name)) {}
+    relation(std::string local_name, std::string remote_name, const object_ptr<LocalType>& local, const ForeignType& remote)
+    : local_name_(std::move(local_name))
+    , remote_name_(std::move(remote_name))
+    , local_(local)
+    , remote_(remote)
+    {}
+
+    template<class Operator>
+    void process(Operator &op) {
+        namespace field = matador::access;
+        field::belongs_to(op, local_name_.c_str(), local_, utils::CascadeNoneFetchLazy);
+        foreign_field(op);
+    }
+
+    object_ptr<LocalType> local() const { return local_; }
+    const ForeignType& remote() const { return remote_; }
+
+private:
+  template<typename Operator, class RemoteType = ForeignType>
+  void foreign_field(Operator &op, std::enable_if_t<!is_object_ptr<RemoteType>::value>* /*unused*/) {
+        namespace field = matador::access;
+        field::attribute(op, remote_name_.c_str(), remote_);
+  }
+  template<typename Operator, class RemoteType = ForeignType>
+  void foreign_field(Operator &op, std::enable_if_t<is_object_ptr<RemoteType>::value>* /*unused*/) {
+        namespace field = matador::access;
+        field::belongs_to(op, remote_name_.c_str(), remote_, utils::CascadeNoneFetchLazy);
+  }
+private:
+    std::string local_name_;
+    std::string remote_name_;
+    object_ptr<LocalType> local_;
+    ForeignType remote_;
+};
+
 template < class LocalType, class ForeignType >
 class many_to_many_relation {
 public:
@@ -15,6 +57,12 @@ public:
     many_to_many_relation(std::string local_name, std::string remote_name)
     : local_name_(std::move(local_name))
     , remote_name_(std::move(remote_name)) {}
+    many_to_many_relation(std::string local_name, std::string remote_name, const object_ptr<LocalType>& local, const object_ptr<ForeignType>& remote)
+    : local_name_(std::move(local_name))
+    , remote_name_(std::move(remote_name))
+    , local_(local)
+    , remote_(remote)
+    {}
 
     template<class Operator>
     void process(Operator &op) {
@@ -40,6 +88,11 @@ public:
     many_to_relation(std::string local_name, std::string remote_name)
     : local_name_(std::move(local_name))
     , type_name_(std::move(remote_name)) {}
+    many_to_relation(std::string local_name, std::string remote_name, const object_ptr<LocalType>& local, const Type& value)
+    : local_name_(std::move(local_name))
+    , type_name_(std::move(remote_name))
+    , local_(local)
+    , value_(value){}
 
     template<class Operator>
     void process(Operator &op) {

include/matador/object/object.hpp

@@ -17,17 +17,21 @@ public:
 
   static const attribute& create_attribute(std::string name, const std::shared_ptr<object>& obj);
 
-  [[nodiscard]] attribute* primary_key_attribute() const;
+  [[nodiscard]] const attribute* primary_key_attribute() const;
   [[nodiscard]] const utils::identifier& primary_key() const;
   [[nodiscard]] bool has_primary_key() const;
 
+  [[nodiscard]] bool is_relation_object() const;
+  [[nodiscard]] const attribute* join_attribute() const;
+  [[nodiscard]] const attribute* inverse_join_attribute() const;
+
   [[nodiscard]] const std::string& name() const;
 
   void update_name(const std::string& name);
 
   [[nodiscard]] bool has_attributes() const;
   [[nodiscard]] size_t attribute_count() const;
-  [[nodiscard]] const std::list<attribute>& attributes() const;
+  [[nodiscard]] const std::vector<attribute>& attributes() const;
 
   [[nodiscard]] bool has_constraints() const;
   [[nodiscard]] size_t constraint_count() const;
@@ -40,9 +44,12 @@ private:
   friend class object_generator;
 
   std::string name_;
-  attribute* pk_attribute_{nullptr};
+  int pk_column_index_{-1};
+  int join_column_index_{-1};
+  int inverse_join_column_index_{-1};
+
   utils::identifier pk_identifier_;
-  std::list<attribute> attributes_;
+  std::vector<attribute> attributes_;
   std::list<restriction> constraints_;
 };
 }

include/matador/object/object_cache.hpp

@@ -5,6 +5,7 @@
 #include "matador/object/object_resolver.hpp"
 
 #include "matador/utils/identifier.hpp"
+#include "matador/utils/message_bus.hpp"
 
 #include <unordered_map>
 #include <memory>
@@ -25,16 +26,33 @@ struct cache_entry_base {
   [[nodiscard]] virtual bool is_dead() const noexcept = 0;
 };
 
-template<typename T>
+template<typename Type>
 struct cache_entry : cache_entry_base {
-  std::weak_ptr<object_proxy<T> > proxy;
+  std::weak_ptr<object_proxy<Type> > proxy;
-  std::weak_ptr<T> entity;
+  std::weak_ptr<Type> entity;
 
   [[nodiscard]] bool is_dead() const noexcept override {
     return proxy.expired() && entity.expired();
   }
 };
 
+struct object_cache_event {
+  std::type_index type{typeid(void)};
+  utils::identifier id{};
+  std::chrono::steady_clock::time_point timestamp{};
+};
+
+struct object_cache_accessed_event : object_cache_event {};
+struct object_cache_proxy_added_event : object_cache_event {};
+struct object_cache_entity_attached_event : object_cache_event {};
+struct object_cache_imported_event : object_cache_event {};
+struct object_cache_erased_event : object_cache_event {};
+
+struct object_cache_sweep_event {
+  std::size_t removed{};
+  std::chrono::steady_clock::time_point timestamp{};
+};
+
 /**
  * @brief Thread-sicherer Cache für Objekt-Proxies und (optional) geladene Entities.
  *
@@ -54,7 +72,8 @@ public:
   /**
    * @brief Erzeugt einen leeren Cache.
    */
-  object_cache() = default;
+  explicit object_cache(utils::message_bus &bus)
+  : bus_(bus) {}
 
   /**
    * @brief Liefert einen Proxy für (T, id) und erstellt ihn bei Bedarf.
@@ -63,8 +82,8 @@ public:
    * Andernfalls wird ein neuer Proxy erzeugt, im Cache abgelegt und zurückgegeben.
    * Falls für (T, id) bereits eine Entity vorhanden ist, wird sie an den Proxy gebunden.
    *
-   * @tparam T Entity-Typ.
+   * @tparam Type Entity-Typ.
-   * @tparam ResolverPtr Zeiger-Typ auf einen Resolver, typischerweise
+   * @tparam ResolverPointerType Zeiger-Typ auf einen Resolver, typischerweise
    *         @c std::shared_ptr<object_resolver<T>> oder @c std::weak_ptr<object_resolver<T>>.
    * @param id Identifier/Primärschlüssel der Entity.
    * @param resolver_ptr Resolver (shared/weak), der zur Lazy-Auflösung durch den Proxy genutzt wird.
@@ -72,23 +91,24 @@ public:
    *
    * @note Diese Methode ist threadsafe.
    */
-  template<typename T, typename ResolverPtr>
+  template<typename Type, typename ResolverPointerType>
-  std::shared_ptr<object_proxy<T>> acquire_proxy(utils::identifier id, ResolverPtr &&resolver_ptr) {
+  std::shared_ptr<object_proxy<Type>> acquire_proxy(utils::identifier id, ResolverPointerType &&resolver_ptr) {
-    const auto k = make_key<T>(id);
+    const auto k = make_key<Type>(id);
 
     std::unique_lock lock(mutex_);
 
     auto it = map_.find(k);
     if (it != map_.end()) {
       // found entry, return std::shared_ptr of proxy
-      auto *entry = entry_cast_<T>(it->second.get());
+      auto *entry = entry_cast_<Type>(it->second.get());
       if (auto proxy_ptr = entry->proxy.lock()) {
+        bus_.publish<object_cache_accessed_event>({k.type, id, std::chrono::steady_clock::now()});
         return proxy_ptr;
       }
 
       // if the proxy is dead, but the entity is alive, create a new proxy and attach entity
-      auto weak_resolver = to_weak<T>(std::forward<ResolverPtr>(resolver_ptr));
+      auto weak_resolver = to_weak<Type>(std::forward<ResolverPointerType>(resolver_ptr));
-      auto proxy_ptr = std::make_shared<object_proxy<T>>(weak_resolver, id);
+      auto proxy_ptr = std::make_shared<object_proxy<Type>>(weak_resolver, id);
 
       if (auto obj = entry->entity.lock()) {
         proxy_ptr->attach(std::move(obj));
@@ -96,17 +116,19 @@ public:
 
       entry->proxy = proxy_ptr;
 
+      bus_.publish<object_cache_proxy_added_event>({k.type, id, std::chrono::steady_clock::now()});
+
       // return the shared_ptr of the proxy
       return proxy_ptr;
     }
 
     // entry couldn't be found, create a new entry
-    auto entry_ptr = std::make_unique<cache_entry<T>>();
+    auto entry_ptr = std::make_unique<cache_entry<Type>>();
     auto *entry = entry_ptr.get();
 
     // create a weak resolver and shared proxy
-    auto weak_resolver = to_weak<T>(std::forward<ResolverPtr>(resolver_ptr));
+    auto weak_resolver = to_weak<Type>(std::forward<ResolverPointerType>(resolver_ptr));
-    auto proxy_ptr = std::make_shared<object_proxy<T>>(weak_resolver, id);
+    auto proxy_ptr = std::make_shared<object_proxy<Type>>(weak_resolver, id);
 
     // lock entity and attach to proxy
     if (auto obj = entry->entity.lock()) {
@@ -117,10 +139,65 @@ public:
     entry->proxy = proxy_ptr;
     map_.emplace(k, std::move(entry_ptr));
 
+    bus_.publish<object_cache_proxy_added_event>({k.type, id, std::chrono::steady_clock::now()});
+
     // return the shared_ptr of the proxy
     return proxy_ptr;
   }
 
+  template<typename Type, typename ResolverPointerType>
+  bool import(const utils::identifier &id, const std::shared_ptr<object_proxy<Type>> &proxy, ResolverPointerType &&resolver_ptr) {
+    if (!proxy) {
+      return false;
+    }
+
+    auto obj = proxy->object();
+    auto weak_resolver = to_weak<Type>(std::forward<ResolverPointerType>(resolver_ptr));
+    const auto k = make_key<Type>(id);
+
+    std::unique_lock lock(mutex_);
+
+    auto it = map_.find(k);
+    if (it != map_.end()) {
+      auto *entry = entry_cast_<Type>(it->second.get());
+
+      if (auto existing_proxy = entry->proxy.lock()) {
+        if (existing_proxy != proxy) {
+          return false;
+        }
+      }
+
+      proxy->primary_key(id);
+      proxy->resolver(std::move(weak_resolver));
+
+      if (obj) {
+        entry->entity = obj;
+        proxy->attach(std::move(obj));
+      }
+
+      entry->proxy = proxy;
+      bus_.publish<object_cache_imported_event>({k.type, id, std::chrono::steady_clock::now()});
+      return true;
+    }
+
+    auto entry_ptr = std::make_unique<cache_entry<Type>>();
+    auto *entry = entry_ptr.get();
+
+    proxy->primary_key(id);
+    proxy->resolver(std::move(weak_resolver));
+
+    if (obj) {
+      entry->entity = obj;
+      proxy->attach(std::move(obj));
+    }
+
+    entry->proxy = proxy;
+    map_.emplace(k, std::move(entry_ptr));
+
+    bus_.publish<object_cache_imported_event>({k.type, id, std::chrono::steady_clock::now()});
+
+    return true;
+  }
   /**
    * @brief Verknüpft eine geladene Entity mit einem Cache-Eintrag (Type, id).
    *
@@ -145,6 +222,7 @@ public:
       auto *entry = entry_ptr.get();
       entry->entity = obj;
       map_.emplace(k, std::move(entry_ptr));
+      bus_.publish<object_cache_entity_attached_event>({k.type, id, std::chrono::steady_clock::now()});
       return;
     }
 
@@ -155,6 +233,8 @@ public:
       proxy->attach(std::move(obj));
     }
 
+    bus_.publish<object_cache_entity_attached_event>({k.type, id, std::chrono::steady_clock::now()});
+
     prune_if_dead(it);
   }
 
@@ -179,6 +259,9 @@ public:
 
     auto *entry = entry_cast_<Type>(it->second.get());
     auto entity_ptr = entry->entity.lock();
+    if (entity_ptr) {
+      bus_.publish<object_cache_accessed_event>({k.type, id, std::chrono::steady_clock::now()});
+    }
     prune_if_dead(it);
     return entity_ptr;
   }
@@ -204,6 +287,9 @@ public:
 
     auto *entry = entry_cast_<Type>(it->second.get());
     const bool loaded = !entry->entity.expired();
+    if (loaded) {
+      bus_.publish<object_cache_accessed_event>({k.type, id, std::chrono::steady_clock::now()});
+    }
     prune_if_dead(it);
     return loaded;
   }
@@ -224,6 +310,7 @@ public:
     }
 
     map_.erase(it);
+    bus_.publish<object_cache_erased_event>({k.type, id, std::chrono::steady_clock::now()});
   }
 
   /**
@@ -246,6 +333,10 @@ public:
       }
     }
 
+    if (removed > 0) {
+      bus_.publish<object_cache_sweep_event>({removed, std::chrono::steady_clock::now()});
+    }
+
     return removed;
   }
 
@@ -286,12 +377,10 @@ private:
   }
 
   template<typename T, typename U>
-  using enable_if_resolver_shared_ptr_t =
+  using enable_if_resolver_shared_ptr_t = std::enable_if_t<std::is_base_of_v<object_resolver<T>, U>, int>;
-    std::enable_if_t<std::is_base_of_v<object_resolver<T>, U>, int>;
 
   template<typename T, typename U>
-  using enable_if_resolver_weak_ptr_t =
+  using enable_if_resolver_weak_ptr_t = std::enable_if_t<std::is_base_of_v<object_resolver<T>, U>, int>;
-    std::enable_if_t<std::is_base_of_v<object_resolver<T>, U>, int>;
 
   // shared_ptr<Derived> -> weak_ptr<Base>
   template<typename T, typename U, enable_if_resolver_shared_ptr_t<T, U> = 0>
@@ -306,8 +395,8 @@ private:
   }
 
   // (2) Opportunistischer Cleanup: entferne Entry, wenn beide weak_ptr abgelaufen sind.
-  template<typename It>
+  template<typename IteratorType>
-  bool prune_if_dead(It &it) {
+  bool prune_if_dead(IteratorType &it) {
     if (it == map_.end()) {
       return false;
     }
@@ -319,14 +408,15 @@ private:
     return false;
   }
 
-  template<typename T>
+  template<typename Type>
   void prune_if_dead_typed(typename std::unordered_map<key, std::unique_ptr<cache_entry_base>, key_hash>::iterator &it) {
-      (void)T{}; // T bleibt im Interface, damit bestehende Call-Sites unverändert bleiben können.
+      (void)Type{}; // T bleibt im Interface, damit bestehende Call-Sites unverändert bleiben können.
       prune_if_dead(it);
   }
 
 private:
   mutable std::shared_mutex mutex_{};
+  utils::message_bus &bus_;
   std::unordered_map<key, std::unique_ptr<cache_entry_base>, key_hash> map_;
 };
 

include/matador/object/object_generator.hpp

@@ -25,17 +25,17 @@ public:
     }
 
     template<typename ValueType>
-    void on_primary_key(const char *, ValueType &/*pk*/, const utils::primary_key_attribute& attr = utils::default_pk_attributes) {
+    void on_primary_key(const char *, ValueType &/*pk*/, const utils::primary_key_attribute& attr) {
         type_ = utils::data_type_traits<ValueType>::type(attr.size());
     }
     static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
     template < class Type >
-    static void on_attribute(const char * /*id*/, Type &/*x*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+    static void on_attribute(const char * /*id*/, Type &/*x*/, const utils::field_attributes &/*attr*/) {}
-    static void on_attribute(const char * /*id*/, char * /*x*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+    static void on_attribute(const char * /*id*/, char * /*x*/, const utils::field_attributes &/*attr*/) {}
     template<class Pointer>
     static void on_belongs_to(const char * /*id*/, Pointer &/*x*/, const utils::foreign_attributes &/*attr*/) {}
     template<class Pointer>
-    static void on_has_one(const char * /*id*/, Pointer &/*x*/, const utils::foreign_attributes &/*attr*/) {}
+    static void on_has_one(const char * /*id*/, Pointer &/*x*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {}
     template<class ContainerType>
     static void on_has_many(const char * /*id*/, ContainerType &, const char *, const utils::foreign_attributes &/*attr*/) {}
     template<class ContainerType>
@@ -58,7 +58,11 @@ public:
     }
 
     template < class Type >
-    static std::shared_ptr<object> generate(std::unique_ptr<Type>&& t, basic_repository &repo, const std::string &name) {
+    static std::shared_ptr<object> generate(std::unique_ptr<Type>&& t,
+                                            basic_repository &repo,
+                                            const std::string &name,
+                                            const std::string &join_column = "",
+                                            const std::string &inverse_join_column = "") {
         const std::type_index ti(typeid(Type));
         if (repo.has_object_for_type(ti)) {
             auto obj = repo.object_for_type(ti);
@@ -71,18 +75,23 @@ public:
         std::ignore = repo.provide_object_in_advance(ti, obj);
         object_generator gen(repo, obj);
         access::process(gen, *t);
+        if (!join_column.empty() && !inverse_join_column.empty()) {
+            gen.prepare_relation_table(join_column, inverse_join_column);
+        }
         return obj;
     }
 
+    template<typename BaseType>
+    static void on_base(const BaseType&) {}
     template < class Type >
-    void on_primary_key(const char *, Type &x, const utils::primary_key_attribute& attr = utils::default_pk_attributes);
+    void on_primary_key(const char *, Type &x, const utils::primary_key_attribute& attr);
     void on_revision(const char *id, uint64_t &rev);
 
     template<typename Type>
-    void on_attribute(const char *id, Type &x, const utils::field_attributes &attr = utils::null_attributes);
+    void on_attribute(const char *id, Type &x, const utils::field_attributes &attr);
 
     template<typename Type>
-    void on_attribute(const char *id, std::optional<Type> &x, const utils::field_attributes &attr = utils::null_attributes);
+    void on_attribute(const char *id, std::optional<Type> &x, const utils::field_attributes &attr);
 
     template<class Pointer>
     void on_belongs_to(const char *id, Pointer &x, const utils::foreign_attributes &/*attr*/) {
@@ -90,12 +99,13 @@ public:
       create_fk_constraint<typename Pointer::value_type>(id);
     }
     template<class Pointer>
-    static void on_has_one(const char * /*id*/, Pointer &/*x*/, const utils::foreign_attributes &/*attr*/) {}
+    static void on_has_one(const char * /*id*/, Pointer &/*x*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {}
 
     template <class Pointer>
     void on_foreign_key(const char *id, Pointer &/*x*/) {
         const auto type = pk_type_determinator::determine<typename Pointer::value_type>();
         auto &ref = object_->attributes_.emplace_back(id, type, utils::constraints::ForeignKey, null_option_type::NotNull);
+        ref.index_ = object_->attributes_.size() - 1;
         ref.owner_ = object_;
     }
     template<class ContainerType>
@@ -109,6 +119,7 @@ private:
     template<typename ValueType>
     attribute &emplace_attribute(const char *id, const utils::field_attributes& attr, null_option_type null_option) {
         auto &ref = object_->attributes_.emplace_back(id, utils::data_type_traits<ValueType>::type(attr.size()), attr, null_option);
+        ref.index_ = object_->attributes_.size() - 1;
         ref.owner_ = object_;
         return ref;
     }
@@ -118,9 +129,10 @@ private:
     void create_fk_constraint(const std::string& name) const;
     void create_unique_constraint(const std::string& name) const;
 
-    [[nodiscard]] std::list<attribute>::iterator find_attribute_by_name(const std::string &name) const;
+    [[nodiscard]] std::vector<attribute>::iterator find_attribute_by_name(const std::string &name) const;
 
-    void prepare_primary_key(attribute &ref, utils::identifier &&pk) const;
+    void prepare_primary_key(const attribute &ref, utils::identifier &&pk) const;
+    void prepare_relation_table(const std::string &join_column, const std::string &inverse_join_column) const;
 
     template<typename Type>
     [[nodiscard]] std::shared_ptr<object> fk_object() const;
@@ -133,7 +145,11 @@ private:
 
 template<typename ValueType>
 void object_generator::on_primary_key(const char *id, ValueType &x, const utils::primary_key_attribute& attr) {
-    auto &ref = emplace_attribute<ValueType>(id, { attr.size(), utils::constraints::PrimaryKey }, null_option_type::NotNull);
+    auto cs = utils::constraints::PrimaryKey;
+    if (attr.generator() == utils::generator_type::Identity) {
+        cs |= utils::constraints::Identity;
+    }
+    auto &ref = emplace_attribute<ValueType>(id, { attr.size(), cs }, null_option_type::NotNull);
     prepare_primary_key(ref, utils::identifier(x));
 }
 
@@ -154,7 +170,7 @@ void object_generator::create_fk_constraint(const std::string& name) const {
         return;
     }
     const auto obj = fk_object<Type>();
-    restriction pk_constraint(*pk_attr);
+    restriction pk_constraint(pk_attr->index());
     pk_constraint.options_ |= utils::constraints::ForeignKey;
     pk_constraint.owner_ = object_;
     pk_constraint.reference_ = obj;

include/matador/object/object_proxy.hpp

@@ -26,86 +26,164 @@ public:
 
   // Lazy
   object_proxy(std::weak_ptr<object_resolver<Type>> resolver, utils::identifier id)
-  : resolver_(resolver)
+  : resolver_(std::move(resolver))
-  , pk_(std::move(id)) {
+  , pk_(std::move(id))
+  , state_(object_state::Persistent) {
   }
 
   // Eager
   object_proxy(std::weak_ptr<object_resolver<Type>> resolver, std::shared_ptr<Type> obj)
-  : obj_(obj)
+  : obj_(std::move(obj))
-  , resolver_(resolver)
+  , resolver_(std::move(resolver))
-  , pk_(primary_key_resolver::resolve_object(*obj).pk)
+  , pk_(obj_ ? primary_key_resolver::resolve_object(*obj_).pk : utils::identifier{})
-  , state_(object_state::Persistent){
+  , state_(obj_ ? object_state::Persistent : object_state::Detached) {
   }
 
   // Transient
   explicit object_proxy(std::shared_ptr<Type> obj)
-  : obj_(obj)
+  : obj_(std::move(obj))
-  , pk_(primary_key_resolver::resolve_object(*obj).pk) {
+  , pk_(obj_ ? primary_key_resolver::resolve_object(*obj_).pk : utils::identifier{}) {
   }
 
   void attach(std::shared_ptr<Type> obj) {
     std::lock_guard lock(mutex_);
+
     obj_ = std::move(obj);
-    if (obj_) {
+    if (!obj_) {
-      pk_ = primary_key_resolver::resolve_object(*obj_).pk;
+      pk_.clear();
-      state_.store(object_state::Persistent, std::memory_order_release);
+      state_ = object_state::Detached;
+      return;
     }
+
+    pk_ = primary_key_resolver::resolve_object(*obj_).pk;
+    state_ = object_state::Persistent;
+  }
+
+  void resolver(std::weak_ptr<object_resolver<Type>> resolver) {
+    std::lock_guard lock(mutex_);
+    resolver_ = std::move(resolver);
+  }
+
+  [[nodiscard]] std::shared_ptr<Type> object() const {
+    return resolve_object();
   }
 
   void invalidate() {
     std::lock_guard lock(mutex_);
     obj_.reset();
     resolver_.reset();
-    state_.store(object_state::Detached, std::memory_order_release);
+    state_ = object_state::Detached;
   }
 
   [[nodiscard]] void *raw_pointer() const { return static_cast<void *>(pointer()); }
 
-  Type *operator->() { return pointer(); }
+  Type *operator->() {
-  Type &operator*() { return *pointer(); }
+    auto *ptr = pointer();
-  const Type &operator*() const { return *pointer(); }
+    if (!ptr) {
+      throw std::runtime_error("Cannot dereference empty object proxy");
+    }
+    return ptr;
+  }
 
-  Type *pointer() const { return resolve(); }
+  const Type *operator->() const {
+    auto *ptr = pointer();
+    if (!ptr) {
+      throw std::runtime_error("Cannot dereference empty object proxy");
+    }
+    return ptr;
+  }
+
+  Type &operator*() {
+    auto *ptr = pointer();
+    if (!ptr) {
+      throw std::runtime_error("Cannot dereference empty object proxy");
+    }
+    return *ptr;
+  }
+
+  const Type &operator*() const {
+    auto *ptr = pointer();
+    if (!ptr) {
+      throw std::runtime_error("Cannot dereference empty object proxy");
+    }
+    return *ptr;
+  }
+
+  Type *pointer() const {
+    return resolve_object().get();
+  }
+
+  [[nodiscard]] bool empty() const {
+    std::lock_guard lock(mutex_);
+    return !obj_ && resolver_.expired();
+  }
 
-  [[nodiscard]] bool empty() const { return !obj_ && resolver_.expired(); }
   [[nodiscard]] bool valid() const { return !empty(); }
-  [[nodiscard]] bool has_primary_key() const { return !pk_.is_null(); }
-  [[nodiscard]] const utils::identifier &primary_key() const { return pk_; }
-  void primary_key(const utils::identifier &pk) { pk_ = pk; }
 
-  bool is_persistent() const { return state_ == object_state::Persistent; }
+  [[nodiscard]] bool has_primary_key() const {
-  bool is_transient() const { return state_ == object_state::Transient; }
+    std::lock_guard lock(mutex_);
-  bool is_detached() const { return state_ == object_state::Detached; }
+    return !pk_.is_null();
-  bool is_removed() const { return state_ == object_state::Removed; }
+  }
+
+  [[nodiscard]] utils::identifier primary_key() const {
+    std::lock_guard lock(mutex_);
+    return pk_;
+  }
+
+  void primary_key(const utils::identifier &pk) {
+    std::lock_guard lock(mutex_);
+    pk_ = pk;
+  }
+
+  bool is_persistent() const { return is_state(object_state::Persistent); }
+  bool is_transient() const { return is_state(object_state::Transient); }
+  bool is_detached() const { return is_state(object_state::Detached); }
+  bool is_removed() const { return is_state(object_state::Removed); }
+
+  bool is_state(const object_state state) const {
+    std::lock_guard lock(mutex_);
+    return state_ == state;
+  }
 
   void change_state(const object_state state) {
-    state_.store(state, std::memory_order_release);
-  }
-private:
-  Type* resolve() const {
-    if (obj_) {
-      return obj_.get();
-    }
-
     std::lock_guard lock(mutex_);
-    auto resolver = resolver_.lock();
+    state_ = state;
-    if (!resolver) {
+  }
-      return nullptr;
+private:
-      // Todo: Add states (Detached, Attached, Transient) - if attached an no resolver is available throw runtime exception
+  std::shared_ptr<Type> resolve_object() const {
-      // throw std::runtime_error("Detached proxy (session expired)");
+    std::shared_ptr<Type> current;
+    std::shared_ptr<object_resolver<Type>> resolver;
+    utils::identifier pk;
+
+    {
+      std::lock_guard lock(mutex_);
+      if (obj_) {
+        return obj_;
+      }
+
+      resolver = resolver_.lock();
+      if (!resolver) {
+        return nullptr;
+      }
+
+      pk = pk_;
     }
 
-    const_cast<std::shared_ptr<Type>&>(obj_) = resolver->resolve(pk_);
+    current = resolver->resolve(pk);
 
-    return obj_.get();
+    {
+      std::lock_guard lock(mutex_);
+      if (!obj_) {
+        obj_ = std::move(current);
+      }
+      return obj_;
+    }
   }
-
 private:
-  std::shared_ptr<Type> obj_{};
+  mutable std::shared_ptr<Type> obj_{};
-  std::weak_ptr<object_resolver<Type>> resolver_{};
+  mutable std::weak_ptr<object_resolver<Type>> resolver_{};
   utils::identifier pk_{};
-  std::atomic<object_state> state_{object_state::Transient};
+  object_state state_{object_state::Transient};
   mutable std::mutex mutex_{};
 };
 }

include/matador/object/object_ptr.hpp

@@ -8,58 +8,161 @@
 #include <memory>
 
 namespace matador::object {
+struct null_object_ptr_t {
+  constexpr null_object_ptr_t() = default;
+};
+
+inline constexpr null_object_ptr_t nullobj{};
+
 template <typename Type>
 class object_ptr {
 public:
-  object_ptr()
+object_ptr()
   : proxy_(std::make_shared<object_proxy<Type>>()) {}
+
+  object_ptr(null_object_ptr_t) {}
+
   explicit object_ptr(std::shared_ptr<Type> obj)
-  : proxy_(std::make_shared<object_proxy<Type>>(obj)) {}
+  : proxy_(std::make_shared<object_proxy<Type>>(std::move(obj))) {}
+
   explicit object_ptr(std::shared_ptr<object_proxy<Type>> obj)
   : proxy_(std::move(obj)) {}
+
   object_ptr(const object_ptr &other) = default;
   object_ptr(object_ptr &&other) noexcept = default;
-  object_ptr &operator=(const object_ptr &other) = default;
+  object_ptr& operator=(const object_ptr &other) = default;
-  object_ptr &operator=(object_ptr &&other) = default;
+  object_ptr& operator=(object_ptr &&other) noexcept = default;
+
+  object_ptr& operator=(null_object_ptr_t) {
+    proxy_.reset();
+    return *this;
+  }
 
   bool operator==(const object_ptr &other) const {
-    return get() == other.get();
+    if (proxy_ == other.proxy_) {
+      return true;
+    }
+
+    if (!proxy_ || !other.proxy_) {
+      return false;
+    }
+
+    if (has_primary_key() && other.has_primary_key()) {
+      return primary_key() == other.primary_key();
+    }
+
+    return false;
   }
+
+  bool operator==(null_object_ptr_t) const {
+    return empty();
+  }
+
   bool operator!=(const object_ptr &other) const { return !operator==(other); }
+  bool operator!=(null_object_ptr_t) const { return !empty(); }
 
   using value_type = Type;
 
-  Type *operator->() const { return get(); }
+  Type *operator->() const {
-  Type &operator*() { return *get(); }
+    return checked_get();
-  const Type &operator*() const { return *get(); }
+  }
 
-  [[nodiscard]] bool empty() const { return get() == nullptr; }
+  Type &operator*() {
+    return *checked_get();
+  }
+
+  const Type &operator*() const {
+    return *checked_get();
+  }
+
+  [[nodiscard]] bool empty() const {
+    return proxy_ == nullptr || proxy_->empty();
+  }
 
   Type *get() const {
     return proxy_ ? proxy_->pointer() : nullptr;
   }
 
-  void reset() { proxy_.reset(); }
+  [[nodiscard]] std::shared_ptr<Type> object() const {
+    return proxy_ ? proxy_->object() : nullptr;
+  }
 
-  operator bool() const { return valid(); }
+  void reset() {
-  [[nodiscard]] bool valid() const { return proxy_ != nullptr; }
+    proxy_.reset();
+  }
 
-  [[nodiscard]] bool has_primary_key() const { return proxy_->has_primary_key(); }
+  void reset(std::shared_ptr<object_proxy<Type>> proxy) {
-  [[nodiscard]] const utils::identifier &primary_key() const { return proxy_->primary_key(); }
+    proxy_ = std::move(proxy);
-  void primary_key(const utils::identifier &pk) { proxy_->primary_key(pk); }
+  }
 
-  [[nodiscard]] bool is_persistent() const { return proxy_->is_persistent(); }
+  [[nodiscard]] std::shared_ptr<object_proxy<Type>> proxy() const {
-  [[nodiscard]] bool is_transient() const { return !proxy_->is_transient(); }
+    return proxy_;
-  [[nodiscard]] bool is_detached() const { return !proxy_->is_detached(); }
+  }
-  [[nodiscard]] bool is_removed() const { return !proxy_->is_removed(); }
 
-  void change_state(object_state s) {
+  explicit operator bool() const {
+    return valid();
+  }
+
+  [[nodiscard]] bool valid() const {
+    return proxy_ != nullptr && !proxy_->empty();
+  }
+
+  [[nodiscard]] bool has_primary_key() const {
+    return proxy_ != nullptr && proxy_->has_primary_key();
+  }
+
+  [[nodiscard]] utils::identifier primary_key() const {
+    return proxy_ ? proxy_->primary_key() : utils::identifier{};
+  }
+
+  void primary_key(const utils::identifier &pk) {
+    ensure_proxy();
+    proxy_->primary_key(pk);
+  }
+
+  [[nodiscard]] bool is_persistent() const {
+    return proxy_ != nullptr && proxy_->is_persistent();
+  }
+
+  [[nodiscard]] bool is_transient() const {
+    return proxy_ != nullptr && proxy_->is_transient();
+  }
+
+  [[nodiscard]] bool is_detached() const {
+    return proxy_ != nullptr && proxy_->is_detached();
+  }
+
+  [[nodiscard]] bool is_removed() const {
+    return proxy_ != nullptr && proxy_->is_removed();
+  }
+
+  [[nodiscard]] bool is_state(const object_state state) const {
+    return proxy_ != nullptr && proxy_->is_state(state);
+  }
+
+  void change_state(object_state s) const {
     if (proxy_) {
       proxy_->change_state(s);
     }
   }
+
 private:
-  std::shared_ptr<object_proxy<Type> > proxy_{};
+  Type *checked_get() const {
+    auto *ptr = get();
+    if (!ptr) {
+      throw std::runtime_error("Cannot dereference empty object_ptr");
+    }
+    return ptr;
+  }
+
+  void ensure_proxy() {
+    if (!proxy_) {
+      proxy_ = std::make_shared<object_proxy<Type>>();
+    }
+  }
+
+private:
+  std::shared_ptr<object_proxy<Type>> proxy_{};
 };
 
 template<typename>

include/matador/object/object_resolver.hpp

@@ -2,6 +2,7 @@
 #define MATADOR_OBJECT_LOADER_HPP
 
 #include "matador/object/abstract_type_resolver.hpp"
+#include "matador/object/abstract_joined_resolver.hpp"
 
 #include <memory>
 
@@ -17,5 +18,13 @@ public:
 
   virtual std::shared_ptr<Type> resolve(const utils::identifier& id) = 0;
 };
+template<typename Type>
+class joined_object_resolver : public abstract_joined_resolver, public object_resolver<Type> {
+public:
+  joined_object_resolver(const std::type_index& root_type, const std::string& join_column)
+  : abstract_joined_resolver(root_type, typeid(Type), join_column) {}
+
+  std::shared_ptr<Type> resolve(const utils::identifier& id) override = 0;
+};
 }
 #endif //MATADOR_OBJECT_LOADER_HPP

include/matador/object/observer.hpp

@@ -113,8 +113,8 @@ class null_observer : public observer<Type> {
 public:
   template < class OtherType >
   explicit null_observer(const null_observer<OtherType> *) {}
-  void on_attach(repository_node &, Type &) override {}
+  void on_attach(const repository_node &, const Type &) const override {}
-  void on_detach(repository_node &, Type &) override {}
+  void on_detach(const repository_node &, const Type &) const override {}
   void on_insert(Type &) override {}
   void on_update(Type &) override {}
   void on_delete(Type &) override {}

include/matador/object/pk_field_locator.hpp

@@ -34,8 +34,10 @@ struct pk_field_locator {
   explicit pk_field_locator (Type &obj)
   : base(&obj) {}
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template <typename PrimaryKeyType>
-  void on_primary_key(const char *, PrimaryKeyType &pk, const utils::primary_key_attribute & = utils::default_pk_attributes) {
+  void on_primary_key(const char *, PrimaryKeyType &pk, const utils::primary_key_attribute & /*attr*/) {
     // Offset bestimmen
     const auto* obj_bytes = reinterpret_cast<std::uint8_t*>(base);
     const auto* pk_bytes = reinterpret_cast<std::uint8_t*>(&pk);
@@ -86,9 +88,11 @@ struct pk_field_locator {
       desc.kind = pk_kind::uuid;
 
       desc.is_known_at = [](void *obj, const std::size_t off) -> bool {
-        auto *p = reinterpret_cast<uuid16 *>(static_cast<std::uint8_t *>(obj) + off);
+        const auto *p = reinterpret_cast<uuid16 *>(static_cast<std::uint8_t *>(obj) + off);
         // “unknown” = all zeros
-        for (auto b: *p) { if (b != 0) return true; }
+        for (const auto b: *p) {
+          if (b != 0) return true;
+        }
         return false;
       };
 
@@ -113,11 +117,11 @@ struct pk_field_locator {
   }
   static void on_revision(const char *, std::uint64_t &) {}
   template <typename V>
-  static void on_attribute(const char *, V &, const utils::field_attributes & = matador::utils::null_attributes) {}
+  static void on_attribute(const char *, V &, const utils::field_attributes &/*attr*/) {}
   template <typename Pointer>
   static void on_belongs_to(const char *, Pointer &, const utils::foreign_attributes &) {}
   template <typename Pointer>
-  static void on_has_one(const char *, Pointer &, const utils::foreign_attributes &) {}
+  static void on_has_one(const char *, Pointer &, const char * /*join_column*/, const utils::foreign_attributes &) {}
   template <typename Container>
   static void on_has_many(const char *, Container &, const char *, const utils::foreign_attributes &) {}
   template <typename Container>

include/matador/object/primary_key_resolver.hpp

@@ -43,8 +43,10 @@ public:
     return resolver.resolve(obj);
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template < class Type >
-  void on_primary_key(const char *id, Type &pk, const utils::primary_key_attribute& attr = utils::default_pk_attributes) {
+  void on_primary_key(const char *id, Type &pk, const utils::primary_key_attribute& attr) {
     primary_key_info_.pk_column_name = id;
     primary_key_info_.type = utils::data_type_traits<Type>::type(attr.size());
     primary_key_info_.pk = pk;
@@ -52,11 +54,11 @@ public:
 
   static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
   template<typename Type>
-  static void on_attribute(const char * /*id*/, Type &/*val*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, Type &/*val*/, const utils::field_attributes &/*attr*/) {}
   template<class Pointer>
   static void on_belongs_to(const char * /*id*/, Pointer &/*val*/, const utils::foreign_attributes &/*attr*/) {}
   template<class Pointer>
-  static void on_has_one(const char * /*id*/, Pointer &/*val*/, const utils::foreign_attributes &/*attr*/) {}
+  static void on_has_one(const char * /*id*/, Pointer &/*val*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {}
   template<class ContainerType>
   static void on_has_many(const char * /*id*/, ContainerType &/*col*/, const char *, const utils::foreign_attributes &/*attr*/) {}
   template<class ContainerType>

include/matador/object/relation_completer.hpp

@@ -28,20 +28,22 @@ public:
         return finder.found_;
     }
 
+    template<typename BaseType>
+    static void on_base(const BaseType&) {}
     template<class PrimaryKeyType>
-    static void on_primary_key(const char * /*id*/, PrimaryKeyType &/*pk*/, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {}
+    static void on_primary_key(const char * /*id*/, PrimaryKeyType &/*pk*/, const utils::primary_key_attribute& /*attr*/) {}
     static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
     template<typename AttributeType>
-    static void on_attribute(const char * /*id*/, AttributeType &/*val*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+    static void on_attribute(const char * /*id*/, AttributeType &/*val*/, const utils::field_attributes &/*attr*/) {}
     template<typename AttributeType>
-    static void on_attribute(const char * /*id*/, std::optional<AttributeType> &/*val*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+    static void on_attribute(const char * /*id*/, std::optional<AttributeType> &/*val*/, const utils::field_attributes &/*attr*/) {}
 
     template<class ForeignPointerType>
     void on_belongs_to(const char *id, ForeignPointerType &/*obj*/, const utils::foreign_attributes &/*attr*/) {
         found_ = requested_join_column_ == id;
     }
     template<class ForeignPointerType>
-    static void on_has_one(const char * /*id*/, ForeignPointerType &/*obj*/, const utils::foreign_attributes &/*attr*/) {}
+    static void on_has_one(const char * /*id*/, ForeignPointerType &/*obj*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {}
 
     template<class CollectionType>
     static void on_has_many(const char * /*id*/, CollectionType &, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {}
@@ -102,18 +104,20 @@ public:
     completer.complete_node_relations(node);
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template<class PrimaryKeyType>
-  static void on_primary_key(const char * /*id*/, PrimaryKeyType &/*pk*/, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {}
+  static void on_primary_key(const char * /*id*/, PrimaryKeyType &/*pk*/, const utils::primary_key_attribute& /*attr*/) {}
   static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
   template<typename AttributeType>
-  static void on_attribute(const char * /*id*/, AttributeType &/*val*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, AttributeType &/*val*/, const utils::field_attributes &/*attr*/) {}
   template<typename AttributeType>
-  static void on_attribute(const char * /*id*/, std::optional<AttributeType> &/*val*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, std::optional<AttributeType> &/*val*/, const utils::field_attributes &/*attr*/) {}
 
   template<class ForeignPointerType>
   void on_belongs_to(const char *id, ForeignPointerType &obj, const utils::foreign_attributes &attr);
   template<class ForeignPointerType>
-  void on_has_one(const char * /*id*/, ForeignPointerType &/*obj*/, const utils::foreign_attributes &/*attr*/);
+  void on_has_one(const char * /*id*/, ForeignPointerType &/*obj*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/);
 
   template<class CollectionType>
   void on_has_many(const char *id, CollectionType &, const char *join_column, const utils::foreign_attributes &attr, std::enable_if_t<is_object_ptr<typename CollectionType::value_type>::value> * = nullptr);
@@ -168,7 +172,7 @@ void relation_completer<Type, Observers...>::on_has_many(const char *id, Collect
   using relation_value_type = many_to_many_relation<Type, value_type>;
 
   // Check if the object_ptr type is already inserted in the schema (by id)
-  auto foreign_node = find_node(typeid(value_type));
+  const auto foreign_node = find_node(typeid(value_type));
   if (!foreign_node) {
     // Todo: throw internal error or attach node
     return;
@@ -187,7 +191,7 @@ void relation_completer<Type, Observers...>::on_has_many(const char *id, Collect
       const auto local_endpoint = std::make_shared<relation_endpoint>(id, relation_type::HasMany, *foreign_node);
       nodes_.top()->info_->register_relation_endpoint(typeid(value_type), local_endpoint);
   } else {
-    // A relation table is necessary
+    // A relation table is necessary.
     // Endpoint was not found.
     // Always attach a many-to-many relation type. If later a
     // belongs-to relation handles this relation, the many-to-many
@@ -218,14 +222,15 @@ template<typename Type, template<typename> typename... Observers>
 template<class CollectionType>
 void relation_completer<Type, Observers...>::on_has_many(const char *id, CollectionType &, const char *join_column,
                                            const utils::foreign_attributes &,
-                                           std::enable_if_t<!is_object_ptr<typename CollectionType::value_type>::value>
+                                           std::enable_if_t<!is_object_ptr<typename CollectionType::value_type>::value>* /*unused*/) {
-                                           * /*unused*/) {
   using value_type = typename CollectionType::value_type;
   using relation_value_type = many_to_relation<Type, value_type>;
 
+  auto observers = internal::observer_list_copy_creator<Type, relation_value_type, Observers...>::copy_create(observers_);
+
   auto node = repository_node::make_node<relation_value_type>(repo_, id, [join_column] {
     return std::make_unique<relation_value_type>(join_column, "value");
-  }, {});
+  }, std::move(observers));
   const auto result = repo_.attach_node(node.release(), "");
   if (!result) {
     // Todo: throw internal exception
@@ -274,6 +279,7 @@ template<typename Type, template<typename> typename... Observers>
 template<class ForeignPointerType>
 void relation_completer<Type, Observers...>::on_has_one(const char *id,
                                           ForeignPointerType &/*obj*/,
+                                          const char * /*join_column*/,
                                           const utils::foreign_attributes &/*attr*/) {
   using value_type = typename ForeignPointerType::value_type;
   const auto foreign_node = find_node(typeid(value_type));
@@ -360,7 +366,12 @@ void relation_completer<Type, Observers...>::attach_relation_node(const std::str
 
   auto observers = internal::observer_list_copy_creator<Type, relation_value_type, Observers...>::copy_create(observers_);
 
-  auto node = repository_node::make_node<relation_value_type>(repo_, name, std::move(creator), std::move(observers));
+  auto node = repository_node::make_relation_node<relation_value_type>(repo_,
+                                                                       name,
+                                                                       join_column,
+                                                                       inverse_join_column,
+                                                                       std::move(creator),
+                                                                       std::move(observers));
   auto result = repo_.attach_node(node.release(), "");
   if (!result) {
     // Todo: throw internal error

include/matador/object/repository_node.hpp

@@ -23,6 +23,13 @@ public:
                                                     const std::string& name,
                                                     creator_func<Type> creator,
                                                     std::vector<std::unique_ptr<observer<Type>>>&& observers);
+  template < typename Type, template<typename> typename... Observers >
+  static std::unique_ptr<repository_node> make_relation_node(basic_repository& repo,
+                                                             const std::string& name,
+                                                             const std::string& join_column,
+                                                             const std::string& inverse_join_column,
+                                                             creator_func<Type> creator,
+                                                             std::vector<std::unique_ptr<observer<Type>>>&& observers);
 
   explicit repository_node(basic_repository& repo);
   repository_node(const repository_node& other) = delete;
@@ -101,5 +108,28 @@ std::unique_ptr<repository_node> repository_node::make_node(basic_repository &re
 
   return node;
 }
+
+template<typename Type, template <typename> class ... Observers>
+std::unique_ptr<repository_node> repository_node::make_relation_node(basic_repository &repo,
+                                                                     const std::string &name,
+                                                                     const std::string &join_column,
+                                                                     const std::string &inverse_join_column,
+                                                                     creator_func<Type> creator,
+                                                                     std::vector<std::unique_ptr<observer<Type>>> &&observers) {
+  const std::type_index ti(typeid(Type));
+  auto node = std::unique_ptr<repository_node>(new repository_node(repo, name, ti));
+
+  internal::observer_list_creator<Type, Observers...>::create_missing(observers);
+
+  auto obj = object_generator::generate<Type>(creator(), repo, name, join_column, inverse_join_column);
+  node->info_.reset(std::make_unique<object_info<Type>>(
+    *node,
+    obj,
+    std::move(observers),
+    std::forward<creator_func<Type>>(creator)
+  ).release());
+
+  return node;
+}
 }
 #endif //REPOSITORY_NODE_HPP

include/matador/object/restriction.hpp

@@ -17,17 +17,17 @@ class object;
 
 class restriction {
 public:
-  explicit restriction(const class attribute& attr);
+  explicit restriction(size_t attr_index);
 
-  [[nodiscard]] const class attribute& attribute() const;
+  [[nodiscard]] size_t attribute_index() const;
   [[nodiscard]] std::string column_name() const;
+  [[nodiscard]] utils::constraints options() const;
   [[nodiscard]] std::shared_ptr<object> owner() const;
   [[nodiscard]] bool is_primary_key_constraint() const;
   [[nodiscard]] bool is_foreign_key_constraint() const;
   [[nodiscard]] bool is_unique_constraint() const;
   [[nodiscard]] std::string ref_table_name() const;
   [[nodiscard]] std::string ref_column_name() const;
-
   friend std::ostream& operator<<(std::ostream& os, const restriction& c);
 
   [[nodiscard]] std::string type_string() const;
@@ -37,7 +37,7 @@ private:
   friend class object_generator;
   friend class object;
 
-  const class attribute& attr_;
+  const size_t index_;
   std::weak_ptr<object> owner_;
   std::weak_ptr<object> reference_;
   utils::constraints options_{utils::constraints::None};

include/matador/orm/error_code.hpp

@@ -1,35 +0,0 @@
-#ifndef ERROR_CODE_HPP
-#define ERROR_CODE_HPP
-
-#include <cstdint>
-#include <system_error>
-
-namespace matador::orm {
-
-enum class error_code : uint8_t {
-  Ok = 0,
-  NoConnectionAvailable,
-  UnknownType,
-  NoPrimaryKey,
-  FailedToBuildQuery,
-  FailedToFindObject,
-  Failed
-};
-
-class orm_category_impl final : public std::error_category
-{
-public:
-    [[nodiscard]] const char* name() const noexcept override;
-    [[nodiscard]] std::string message(int ev) const override;
-};
-
-const std::error_category& orm_category();
-std::error_code make_error_code(error_code e);
-std::error_condition make_error_condition(error_code e);
-
-}
-
-template <>
-struct std::is_error_code_enum<matador::orm::error_code> : true_type {};
-
-#endif //ERROR_CODE_HPP

include/matador/orm/session.hpp

@@ -1,338 +0,0 @@
-#ifndef QUERY_SESSION_HPP
-#define QUERY_SESSION_HPP
-
-#include "matador/orm/error_code.hpp"
-
-#include "matador/query/select_query_builder.hpp"
-#include "matador/query/criteria.hpp"
-#include "matador/query/insert_query_builder.hpp"
-#include "matador/query/query.hpp"
-#include "matador/query/generator.hpp"
-#include "matador/query/schema.hpp"
-
-#include "matador/sql/connection.hpp"
-#include "matador/sql/connection_pool.hpp"
-#include "matador/sql/executor.hpp"
-#include "matador/sql/resolver_service.hpp"
-#include "matador/sql/statement.hpp"
-#include "matador/sql/statement_cache.hpp"
-
-#include "matador/object/object_ptr.hpp"
-
-#include <unordered_map>
-#include <utility>
-
-namespace matador::orm {
-utils::error make_error(error_code ec, const std::string &msg);
-
-struct session_context {
-  session_context(utils::message_bus &bus, std::string dns, const size_t count, const size_t cache_size = 500)
-  : bus(bus)
-  , dns(std::move(dns))
-  , connection_count(count)
-  , cache_size(cache_size) {
-  }
-  utils::message_bus &bus;
-  std::string dns;
-  size_t connection_count{};
-  size_t cache_size{500};
-  std::shared_ptr<sql::resolver_service> resolver_service = std::make_shared<sql::resolver_service>();
-};
-
-class session final : public sql::executor {
-public:
-  session(session_context &&ctx, const query::schema &scm);
-
-  /**
-   * Insert the given object into the session.
-   *
-   * @tparam Type Type of object to insert
-   * @param obj Object to insert
-   * @return Inserted object
-   */
-  template<typename Type>
-  utils::result<object::object_ptr<Type>, utils::error> insert(object::object_ptr<Type> obj);
-
-  template<typename Type>
-  utils::result<object::object_ptr<Type>, utils::error> update(const object::object_ptr<Type> &obj);
-  template<typename Type>
-  utils::result<void, utils::error> remove(const object::object_ptr<Type> &obj);
-
-  template<typename Type, typename PrimaryKeyType>
-  utils::result<object::object_ptr<Type>, utils::error> find(const PrimaryKeyType &pk);
-  template<typename Type>
-  utils::result<sql::query_result<Type>, utils::error> find(query::criteria_ptr clause = {});
-
-  template<typename Type>
-  utils::result<void, utils::error> drop_table() const;
-  utils::result<void, utils::error> drop_table(const std::string &table_name) const;
-
-  [[nodiscard]] utils::result<sql::query_result<sql::record>, utils::error> fetch_all(const sql::query_context &q) const;
-  [[nodiscard]] utils::result<sql::execute_result, utils::error> execute(const std::string &sql) const;
-
-  [[nodiscard]] std::vector<object::attribute> describe_table(const std::string &table_name) const;
-  [[nodiscard]] bool table_exists(const std::string &table_name) const;
-
-  [[nodiscard]] utils::result<std::unique_ptr<sql::query_result_impl>, utils::error> fetch(const sql::query_context &ctx) const override;
-  [[nodiscard]] utils::result<sql::execute_result, utils::error> execute(const sql::query_context &ctx) const override;
-  [[nodiscard]] utils::result<sql::statement, utils::error> prepare(const sql::query_context &ctx) override;
-  [[nodiscard]] std::string str(const sql::query_context &ctx) const override;
-  [[nodiscard]] const sql::dialect &dialect() const override;
-  [[nodiscard]] std::shared_ptr<sql::resolver_service> resolver() const override;
-  [[nodiscard]] const query::basic_schema &schema() const;
-
-private:
-  sql::connection_pool pool_;
-  mutable sql::statement_cache cache_;
-  const sql::dialect &dialect_;
-
-  const query::basic_schema &schema_;
-  mutable std::unordered_map<std::string, std::vector<object::attribute> > prototypes_;
-  std::shared_ptr<sql::resolver_service> resolver_service_;
-};
-
-template<typename Type>
-utils::result<object::object_ptr<Type>, utils::error> session::insert(object::object_ptr<Type> obj) {
-  if (obj.is_persistent()) {
-    return utils::ok(obj);
-  }
-
-  const auto it = schema_.find(typeid(Type));
-  if (it == schema_.end()) {
-    return utils::failure(make_error(error_code::UnknownType, "Failed to determine requested type."));
-  }
-
-  // Build dependency-ordered insert steps (deps first, root last)
-  query::insert_query_builder iqb(schema_);
-  auto steps = iqb.build(obj);
-  if (!steps.is_ok()) {
-    return utils::failure(make_error(error_code::FailedToBuildQuery, "Failed to build insert dependency queries."));
-  }
-
-  // Execute all steps; for Identity steps read RETURNING and write pk back into the object
-  for (auto &step : *steps) {
-    if (step.pk_is_unset && step.set_pk) {
-      if (step.pk_generator == utils::generator_type::Manually) {
-        if (step.pk_is_unset()) {
-          return utils::failure(make_error(error_code::NoPrimaryKey, "Manual primary key is required but unset."));
-        }
-      } else if (step.pk_generator == utils::generator_type::Sequence) {
-        if (step.pk_is_unset()) {
-          // hard-coded naming as you specified earlier
-          // <table_name>_seq (table name known in schema meta; if you prefer, store it in step too)
-          // For now, we derive from the schema type used for the root insert: simplistic but works if table name == entity name.
-          const std::string seq_name = it->second.name() + "_seq";
-
-          auto id_res = query::query::select().nextval(seq_name).fetch_value<std::uint64_t>(*this);
-          if (!id_res.is_ok() || !id_res.value().has_value()) {
-            return utils::failure(make_error(error_code::FailedToBuildQuery, "Failed to obtain next sequence value."));
-          }
-          step.set_pk(*id_res.value());
-        }
-      } else if (step.pk_generator == utils::generator_type::Table) {
-        if (step.pk_is_unset()) {
-          // TODO: implement table id generation; same idea as above:
-          // UPDATE <table>_tbl_seq ... RETURNING ...
-          return utils::failure(make_error(error_code::Failed, "Table primary key generator not implemented yet."));
-        }
-      }
-    }
-
-    // --- Execute step ---
-    if (std::holds_alternative<query::executable_query>(step.query)) {
-      const auto &q = std::get<query::executable_query>(step.query);
-      const auto exec_res = q.execute(*this);
-      if (!exec_res.is_ok()) {
-        return utils::failure(exec_res.err());
-      }
-      continue;
-    }
-
-    const auto &q = std::get<query::fetchable_query>(step.query);
-    auto rec_res = q.fetch_one(*this);
-    if (!rec_res.is_ok()) {
-      return utils::failure(rec_res.err());
-    }
-    if (!rec_res.value().has_value()) {
-      return utils::failure(make_error(error_code::FailedToFindObject, "INSERT ... RETURNING did not return a row."));
-    }
-    if (step.apply_returning) {
-      step.apply_returning(*rec_res.value());
-    }
-  }
-
-  obj.change_state(object::object_state::Persistent);
-  return utils::ok(obj);
-}
-
-class pk_object_binder final {
-public:
-  explicit pk_object_binder(sql::statement &stmt, const size_t position)
-  : stmt_(stmt)
-  , binding_position_(position) {
-  }
-
-  template<class Type>
-  sql::statement &bind(Type &obj) {
-    access::process(*this, obj);
-    return stmt_;
-  }
-
-  template<class Type>
-  void on_primary_key(const char * /*id*/, Type &x, const utils::primary_key_attribute & /*attr*/ = utils::default_pk_attributes) {
-    stmt_.bind(binding_position_, x);
-  }
-
-  static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {
-  }
-
-  template<class Type>
-  static void on_attribute(const char * /*id*/, Type &/*x*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
-  template<class Pointer>
-  static void on_belongs_to(const char * /*id*/, Pointer &/*x*/, const utils::foreign_attributes &/*attr*/ = utils::CascadeNoneFetchLazy) {}
-  template<class Pointer>
-  static void on_has_one(const char * /*id*/, Pointer &/*x*/, const utils::foreign_attributes &/*attr*/ = utils::CascadeNoneFetchLazy) {}
-
-  template<class ContainerType>
-  static void on_has_many(const char * /*id*/,
-                          ContainerType &/*c*/,
-                          const char * /*join_column*/,
-                          const utils::foreign_attributes &/*attr*/ = utils::CascadeNoneFetchLazy) {}
-
-  template<class ContainerType>
-  static void on_has_many_to_many(const char * /*id*/,
-                                  ContainerType &/*c*/,
-                                  const char * /*join_column*/,
-                                  const char * /*inverse_join_column*/,
-                                  const utils::foreign_attributes &/*attr*/) {}
-
-  template<class ContainerType>
-  static void on_has_many_to_many(const char * /*id*/,
-                                  ContainerType &/*c*/,
-                                  const utils::foreign_attributes &/*attr*/) {}
-
-private:
-  sql::statement &stmt_;
-  size_t binding_position_{0};
-  sql::object_pk_binder pk_binder_{};
-};
-
-template<typename Type>
-utils::result<object::object_ptr<Type>, utils::error> session::update(const object::object_ptr<Type> &obj) {
-  const auto it = schema_.find(typeid(Type));
-  if (it == schema_.end()) {
-    return utils::failure(make_error(error_code::UnknownType, "Failed to determine requested type."));
-  }
-  using namespace matador::utils;
-  using namespace matador::query;
-
-  const auto col = table_column(it->second.node().info().primary_key_attribute()->name());
-  auto res = matador::query::query::update(it->second.name())
-    .set(generator::column_value_pairs<Type>())
-    .where(col == _)
-    .prepare(*this);
-  if (!res) {
-    return utils::failure(res.err());
-  }
-
-  res->bind(*obj);
-  pk_object_binder binder(res.value(), res->bind_pos());
-  if (const auto update_result = binder.bind(*obj).execute(); !update_result.is_ok()) {
-    return utils::failure(update_result.err());
-  }
-  return utils::ok(object::object_ptr{obj});
-}
-
-template<typename Type>
-utils::result<void, utils::error> session::remove(const object::object_ptr<Type> &obj) {
-  const auto it = schema_.find(typeid(Type));
-  if (it == schema_.end()) {
-    return utils::failure(make_error(error_code::UnknownType, "Failed to determine requested type."));
-  }
-  using namespace matador::utils;
-  using namespace matador::query;
-
-  const auto col = table_column(it->second.node().info().primary_key_attribute()->name());
-  auto res = matador::query::query::remove()
-    .from(it->second.name())
-    .where(col == _)
-    .prepare(*this);
-  if (!res) {
-    return utils::failure(res.err());
-  }
-
-  pk_object_binder binder(res.value(), res->bind_pos());
-  if (const auto update_result = binder.bind(*obj).execute(); !update_result.is_ok()) {
-    return utils::failure(update_result.err());
-  }
-  return utils::ok<void>();
-}
-
-template<typename Type, typename PrimaryKeyType>
-utils::result<object::object_ptr<Type>, utils::error> session::find(const PrimaryKeyType &pk) {
-  const auto it = schema_.find(typeid(Type));
-  if (it == schema_.end()) {
-    return utils::failure(make_error(error_code::UnknownType, "Failed to determine requested type."));
-  }
-  const auto &info = it->second.node().info();
-  if (!info.has_primary_key()) {
-    return utils::failure(make_error(error_code::NoPrimaryKey, "Type hasn't primary key."));
-  }
-
-  query::select_query_builder eqb(schema_);
-  const query::table_column c(&it->second.table(), info.primary_key_attribute()->name());
-  using namespace matador::query;
-  auto data = eqb.build<Type>(c == utils::_);
-  if (!data.is_ok()) {
-    return utils::failure(make_error(error_code::FailedToBuildQuery,
-                                     "Failed to build query for type " + info.name() + "."));
-  }
-
-  auto res = data->prepare(*this);
-
-  if (!res) {
-    return utils::failure(res.err());
-  }
-  auto stmt_result = res->bind(0, const_cast<PrimaryKeyType &>(pk))
-    .template fetch_one<Type>();
-  if (!stmt_result) {
-    return utils::failure(make_error(error_code::FailedToFindObject,
-                                     "Failed to find object of type " + info.name() + " with primary key " +
-                                     std::to_string(pk) + "."));
-  }
-  return utils::ok(*stmt_result);
-}
-
-template<typename Type>
-utils::result<sql::query_result<Type>, utils::error> session::find(query::criteria_ptr clause) {
-  const auto it = schema_.find(typeid(Type));
-  if (it == schema_.end()) {
-    return utils::failure(make_error(error_code::UnknownType, "Failed to determine requested type."));
-  }
-
-  query::select_query_builder eqb(schema_);
-  auto data = eqb.build<Type>(std::move(clause));
-  if (!data.is_ok()) {
-    return utils::failure(make_error(error_code::FailedToBuildQuery,
-                                     "Failed to build query for type " + it->second.name() + "."));
-  }
-
-  auto result = data->prepare(*this);
-  if (!result.is_ok()) {
-    return utils::failure(result.err());
-  }
-
-  return result->template fetch<Type>();
-}
-
-template<typename Type>
-utils::result<void, utils::error> session::drop_table() const {
-  const auto it = schema_.find(typeid(Type));
-  if (it == schema_.end()) {
-    return utils::failure(make_error(error_code::UnknownType, "Failed to determine requested type."));
-  }
-  return drop_table(it->second.name());
-}
-
-}
-#endif //QUERY_SESSION_HPP

include/matador/query/abstract_pk_generator.hpp

@@ -3,6 +3,7 @@
 
 #include "matador/utils/error.hpp"
 #include "matador/utils/result.hpp"
+#include "matador/utils/primary_key_generator_type.hpp"
 
 #include <cstdint>
 
@@ -14,6 +15,15 @@ class abstract_pk_generator {
 public:
   virtual ~abstract_pk_generator() = default;
   virtual utils::result<int64_t, utils::error> next_id(const sql::executor& exec) = 0;
+  virtual utils::result<int64_t, utils::error> current_id(const sql::executor& exec) = 0;
+
+  [[nodiscard]] utils::generator_type type() const;
+
+protected:
+  explicit abstract_pk_generator(utils::generator_type type);
+
+private:
+  utils::generator_type generator_type_{};
 };
 }
 #endif //MATADOR_ABSTRACT_PK_GENERATOR_HPP

include/matador/query/attribute_string_writer.hpp

@@ -3,17 +3,13 @@
 
 #include "matador/utils/attribute_writer.hpp"
 
-#include <optional>
+#include "matador/sql/interface/connection_impl.hpp"
 
-namespace matador::sql {
+#include <optional>
-class dialect;
-class connection_impl;
-}
 
 namespace matador::query {
 
-class attribute_string_writer final : public utils::attribute_writer
+class attribute_string_writer final : public utils::attribute_writer {
-{
 public:
   attribute_string_writer(const sql::dialect &d, std::optional<std::reference_wrapper<const sql::connection_impl>> conn);
 

include/matador/query/basic_schema.hpp

@@ -1,31 +1,36 @@
 #ifndef MATADOR_BASIC_SCHEMA_HPP
 #define MATADOR_BASIC_SCHEMA_HPP
 
+#include "matador/object/repository.hpp"
+
+#include "matador/query/abstract_pk_generator.hpp"
+#include "matador/query/table.hpp"
+
+#include "matador/sql/internal/joined_collection_resolver_producer.hpp"
+#include "matador/sql/internal/object_resolver_producer.hpp"
+#include "matador/sql/producer_object_resolver_factory.hpp"
+
 #include <memory>
 #include <typeindex>
 #include <unordered_map>
 
-#include "matador/object/repository.hpp"
+namespace matador::sql {
-
+class connection;
-#include "matador/query/table.hpp"
+}
-
-#include "matador/sql/internal/collection_resolver_producer.hpp"
-#include "matador/sql/internal/object_resolver_producer.hpp"
-#include "matador/sql/producer_resolver_factory.hpp"
 
 namespace matador::query {
 class schema_node final {
 public:
-  schema_node(class table tab, utils::generator_type generator_type, const object::repository_node& node);
+  schema_node(class table tab, std::unique_ptr<abstract_pk_generator> &&pk_generator, const object::repository_node& node);
 
   [[nodiscard]] const std::string& name() const;
   [[nodiscard]] const class table& table() const;
-  [[nodiscard]] utils::generator_type generator_type() const;
+  [[nodiscard]] abstract_pk_generator& pk_generator() const;
   [[nodiscard]] const object::repository_node& node() const;
 
 private:
   class table table_;
-  utils::generator_type generator_type_{};
+  std::unique_ptr<abstract_pk_generator> pk_generator_;
   const object::repository_node& node_;
 };
 
@@ -33,23 +38,25 @@ class primary_key_generator_finder final {
 public:
   template< typename Type >
   utils::generator_type find(const object::object_info<Type>& info) {
-    generator_type_ = utils::generator_type::Manually;
+    generator_type_ = utils::generator_type::Manual;
 
     access::process(*this, info.prototype());
 
     return generator_type_;
   }
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template<class V>
-  void on_primary_key(const char * /*id*/, V &/*pk*/, const utils::primary_key_attribute &attr = utils::default_pk_attributes) {
+  void on_primary_key(const char * /*id*/, V &/*pk*/, const utils::primary_key_attribute &attr) {
     generator_type_ = attr.generator();
   }
   static void on_revision(const char * /*id*/, uint64_t & /*rev*/) {}
   template<typename T>
-  static void on_attribute(const char * /*id*/, T &, const utils::field_attributes & = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, T &, const utils::field_attributes &/*attr*/) {}
   template<class P>
   static void on_belongs_to(const char * /*id*/, P &, const utils::foreign_attributes & ) {}
   template<class P>
-  static void on_has_one(const char * /*id*/, P &, const utils::foreign_attributes & ) {}
+  static void on_has_one(const char * /*id*/, P &, const char * /*join_column*/, const utils::foreign_attributes & ) {}
   template<class C>
   static void on_has_many(const char * /*id*/, C &, const char * /*join_column*/, const utils::foreign_attributes & ) {}
   template<class C>
@@ -70,6 +77,14 @@ public:
   basic_schema();
   explicit basic_schema(const std::string &name);
 
+  [[nodiscard]] std::string name() const;
+
+  [[nodiscard]] const object::repository &repo() const;
+  object::repository &repo();
+
+  [[nodiscard]] utils::result<void, utils::error> create(const sql::connection &conn) const;
+  [[nodiscard]] utils::result<void, utils::error> drop(const sql::connection &conn) const;
+
   iterator begin();
   iterator end();
   [[nodiscard]] const_iterator begin() const;
@@ -86,7 +101,9 @@ public:
 
   [[nodiscard]] bool contains(const std::type_index &index) const;
 
-  void initialize_executor(sql::executor &exec) const;
+  [[nodiscard]] const std::unordered_map<std::type_index, std::unique_ptr<sql::object_resolver_producer>>& resolver_producers() const;
+  [[nodiscard]] const std::unordered_map<object::collection_composite_key, std::unique_ptr<sql::joined_collection_resolver_producer>, object::collection_composite_key_hash>& collection_resolver_producers() const;
+  [[nodiscard]] const std::unordered_map<object::collection_composite_key, std::unique_ptr<sql::joined_object_resolver_producer>, object::collection_composite_key_hash>& joined_object_resolver_producers() const;
 
 protected:
   template<typename Type>
@@ -96,7 +113,8 @@ protected:
   object::repository repo_;
   std::unordered_map<std::type_index, schema_node> schema_nodes_;
   std::unordered_map<std::type_index, std::unique_ptr<sql::object_resolver_producer>> resolver_producers_;
-  std::unordered_map<object::collection_composite_key, std::unique_ptr<sql::collection_resolver_producer>, object::collection_composite_key_hash> collection_resolver_producers_;
+  std::unordered_map<object::collection_composite_key, std::unique_ptr<sql::joined_collection_resolver_producer>, object::collection_composite_key_hash> collection_resolver_producers_;
+  std::unordered_map<object::collection_composite_key, std::unique_ptr<sql::joined_object_resolver_producer>, object::collection_composite_key_hash> joined_object_resolver_producers_;
 };
 }
 #endif //MATADOR_BASIC_SCHEMA_HPP

include/matador/query/builder.hpp

@@ -8,36 +8,39 @@
 #include "matador/utils/basic_types.hpp"
 #include "matador/utils/constraints.hpp"
 #include "matador/utils/data_type_traits.hpp"
+#include "matador/utils/types.hpp"
 
 #include <string>
 
 namespace matador::object {
-
 class data_type {
 public:
-    explicit data_type(const utils::basic_type type, const size_t size = 0)
+  explicit data_type(const utils::basic_type type, const size_t size = 0)
-    : type_(type), size_(size) {}
+  : type_(type), size_(size) {
+  }
 
-    [[nodiscard]] const utils::basic_type& type() const { return type_; }
+  [[nodiscard]] const utils::basic_type &type() const { return type_; }
-    [[nodiscard]] size_t size() const { return size_; }
+  [[nodiscard]] size_t size() const { return size_; }
 
 private:
-    utils::basic_type type_{};
+  utils::basic_type type_{};
-    size_t size_{0};
+  size_t size_{0};
 };
 
 template<typename Type>
 class typed_data_type final : public data_type {
 public:
-    typed_data_type()
+  typed_data_type()
-    : data_type(utils::data_type_traits<Type>::type()) {}
+  : data_type(utils::data_type_traits<Type>::type()) {
+  }
 };
 
 template<typename Type>
 class sized_typed_data_type final : public data_type {
 public:
-    explicit sized_typed_data_type(size_t size)
+  explicit sized_typed_data_type(size_t size)
-    : data_type(utils::data_type_traits<Type>::type(size), size) {}
+  : data_type(utils::data_type_traits<Type>::type(size), size) {
+  }
 };
 
 using TinyInt = typed_data_type<int8_t>;
@@ -55,11 +58,14 @@ using Double = typed_data_type<double>;
 using Text = typed_data_type<std::string>;
 using Boolean = typed_data_type<bool>;
 using Varchar = sized_typed_data_type<std::string>;
-using Blob = sized_typed_data_type<std::vector<std::byte>>;
+using Blob = sized_typed_data_type<std::vector<std::byte> >;
 
+using Time = typed_data_type<utils::time_type_t>;
+using Date = typed_data_type<utils::date_type_t>;
+using Timestamp = typed_data_type<utils::timestamp_type_t>;
 }
-namespace matador::query {
 
+namespace matador::query {
 class column_builder {
 public:
   explicit column_builder(std::string column_name, utils::basic_type type, size_t size = 0);
@@ -67,10 +73,10 @@ public:
   // ReSharper disable once CppNonExplicitConversionOperator
   operator table_column() const; // NOLINT(*-explicit-constructor)
 
-  column_builder& not_null();
+  column_builder &not_null();
-  column_builder& primary_key();
+  column_builder &primary_key();
-  column_builder& unique();
+  column_builder &unique();
-  column_builder& identity();
+  column_builder &identity();
 
 private:
   std::string column_name_;
@@ -87,15 +93,15 @@ public:
   operator table() const; // NOLINT(*-explicit-constructor)
 
 private:
-    std::string table_name;
+  std::string table_name;
 };
 
 class constraint_builder {
 public:
-  constraint_builder& constraint(std::string name);
+  constraint_builder &constraint(std::string name);
-  constraint_builder& primary_key(std::string name);
+  constraint_builder &primary_key(std::string name);
-  constraint_builder& foreign_key(std::string name);
+  constraint_builder &foreign_key(std::string name);
-  constraint_builder& references(std::string table, std::string column);
+  constraint_builder &references(std::string table, std::string column);
 
   // ReSharper disable once CppNonExplicitConversionOperator
   operator table_constraint() const; // NOLINT(*-explicit-constructor)
@@ -111,6 +117,5 @@ private:
 constraint_builder constraint(std::string name);
 // table_builder table(std::string name);
 column_builder column(std::string name, utils::basic_type type, size_t size = 0);
-
 }
 #endif //MATADOR_BUILDER_HPP

include/matador/query/criteria/binary_criteria.hpp

@@ -8,12 +8,12 @@
 
 namespace matador::query {
 enum class binary_operator {
-    EQUALS,
+    Equals,
-    NOT_EQUALS,
+    NotEquals,
-    GREATER_THAN,
+    GreaterThan,
-    GREATER_THAN_OR_EQUAL,
+    GreaterThanOrEqual,
-    LESS_THAN,
+    LessThan,
-    LESS_THAN_OR_EQUAL,
+    LessThanOrEqual,
 };
 
 class binary_criteria final : public abstract_column_criteria {

include/matador/query/criteria/criteria_operators.hpp

@@ -20,33 +20,33 @@ class table_column;
 template<class Type>
 std::enable_if_t<!std::is_base_of_v<fetchable_query, std::decay_t<Type>>, criteria_ptr>
 operator==(const table_column &col, Type val) {
-    return std::make_unique<binary_criteria>(col, binary_operator::EQUALS, utils::value(val));
+    return std::make_unique<binary_criteria>(col, binary_operator::Equals, utils::value(val));
 }
 
 template<class Type>
 std::enable_if_t<!std::is_base_of_v<fetchable_query, std::decay_t<Type>>, criteria_ptr>
 operator!=(const table_column &col, Type val) {
-    return std::make_unique<binary_criteria>(col, binary_operator::NOT_EQUALS, utils::value(val));
+    return std::make_unique<binary_criteria>(col, binary_operator::NotEquals, utils::value(val));
 }
 
 template<class Type>
 criteria_ptr operator>(const table_column &col, Type val) {
-    return std::make_unique<binary_criteria>(col, binary_operator::GREATER_THAN, utils::value(val));
+    return std::make_unique<binary_criteria>(col, binary_operator::GreaterThan, utils::value(val));
 }
 
 template<class Type>
 criteria_ptr operator>=(const table_column &col, Type val) {
-    return std::make_unique<binary_criteria>(col, binary_operator::GREATER_THAN_OR_EQUAL, utils::value(val));
+    return std::make_unique<binary_criteria>(col, binary_operator::GreaterThanOrEqual, utils::value(val));
 }
 
 template<class Type>
 criteria_ptr operator<(const table_column &col, Type val) {
-    return std::make_unique<binary_criteria>(col, binary_operator::LESS_THAN, utils::value(val));
+    return std::make_unique<binary_criteria>(col, binary_operator::LessThan, utils::value(val));
 }
 
 template<class Type>
 criteria_ptr operator<=(const table_column &col, Type val) {
-    return std::make_unique<binary_criteria>(col, binary_operator::LESS_THAN_OR_EQUAL, utils::value(val));
+    return std::make_unique<binary_criteria>(col, binary_operator::LessThanOrEqual, utils::value(val));
 }
 
 criteria_ptr operator==(const table_column &col_left, const table_column &col_right);

include/matador/query/database.hpp

@@ -0,0 +1,20 @@
+#ifndef MATADOR_DATABASE_HPP
+#define MATADOR_DATABASE_HPP
+
+#include "matador/query/schema.hpp"
+#include "matador/utils/result.hpp"
+#include "matador/utils/error.hpp"
+
+namespace matador::query {
+class database final {
+public:
+  utils::result<void, utils::error> add(const std::string &name, const schema &schema);
+  utils::result<void, utils::error> remove(const std::string &name);
+
+  [[nodiscard]] utils::result<schema_ref, utils::error> get(const std::string &name);
+
+private:
+  std::unordered_map<std::string, schema> schema_map_;
+};
+}
+#endif //MATADOR_DATABASE_HPP

include/matador/query/delete_query_builder.hpp

@@ -0,0 +1,272 @@
+#ifndef MATADOR_DELETE_QUERY_BUILDER_HPP
+#define MATADOR_DELETE_QUERY_BUILDER_HPP
+
+#include "matador/object/collection.hpp"
+#include "matador/object/object_cache.hpp"
+#include "matador/object/object_ptr.hpp"
+
+#include "matador/query/basic_schema.hpp"
+#include "matador/query/error_code.hpp"
+#include "matador/query/delete_step.hpp"
+#include "matador/query/query_contexts.hpp"
+#include "matador/query/query_builder_exception.hpp"
+#include "matador/query/query_builder_utils.hpp"
+
+#include "matador/sql/statement.hpp"
+
+#include "matador/utils/error.hpp"
+#include "matador/utils/identifier.hpp"
+#include "matador/utils/primary_key_accessor.hpp"
+#include "matador/utils/result.hpp"
+
+namespace matador::query {
+template<typename ObjectType>
+class delete_step_processor {
+public:
+  explicit delete_step_processor(query_builder_context &ctx)
+  : ctx_(ctx) {}
+
+  utils::result<void, utils::error> build(object::object_ptr<ObjectType> ptr, const bool as_relation_step = false) {
+    if (!ptr) {
+      return utils::failure(utils::error{error_code::InvalidObject, "Object is null"});
+    }
+
+    ptr_ = ptr;
+
+    const auto key = make_entity_visit_key<ObjectType>(*ptr_);
+    if (ctx_.visited_.find(key) != ctx_.visited_.end()) {
+      return utils::ok<void>();
+    }
+    ctx_.visited_.insert(key);
+
+    const auto it = ctx_.schema_.find(typeid(ObjectType));
+    if (it == ctx_.schema_.end()) {
+      return utils::failure(utils::error{error_code::UnknownType, "Unknown type"});
+    }
+
+    if (const auto &info = it->second.node().info(); !info.has_primary_key()) {
+      return utils::failure(utils::error{error_code::MissingPrimaryKey, "Type " + info.name() + " has no primary key"});
+    }
+
+    try {
+      access::process(*this, *ptr_);
+    } catch (const query_builder_exception &ex) {
+      return utils::failure(ex.error());
+    }
+
+    const auto cit = ctx_.contexts_by_type_.find(it->second.node().info().type_index());
+    if (cit == ctx_.contexts_by_type_.end()) {
+      return utils::failure(utils::error{error_code::UnknownType, "Unknown type"});
+    }
+
+    if (as_relation_step) {
+      ctx_.relation_steps_.push_back(std::make_unique<delete_step_object<ObjectType>>(cit->second.delete_one, ptr_));
+    } else {
+      ctx_.steps_.push_back(std::make_unique<delete_step_object<ObjectType>>(cit->second.delete_one, ptr_));
+    }
+
+    ptr_.reset();
+
+    return utils::ok<void>();
+  }
+
+  template<class PrimaryKeyType>
+  static void on_primary_key(const char * /*id*/, PrimaryKeyType &, const utils::primary_key_attribute & /*attr*/) {}
+
+  static void on_revision(const char * /*id*/, uint64_t & /*rev*/) {}
+
+  template<typename Type>
+  static void on_attribute(const char * /*id*/, Type &, const utils::field_attributes & /*attr*/) {}
+
+  template<class Pointer>
+  void on_belongs_to(const char * /*id*/, Pointer &obj, const utils::foreign_attributes &attr) {
+    on_foreign_object(obj, attr);
+  }
+
+  template<class Pointer>
+  void on_has_one(const char * /*id*/, Pointer &obj, const char * /*join_column*/, const utils::foreign_attributes &attr) {
+    on_foreign_object(obj, attr);
+  }
+
+  template<class CollectionType>
+  void on_has_many(const char * /*id*/,
+                   object::collection<object::object_ptr<CollectionType>> &objects,
+                   const char *join_column,
+                   const utils::foreign_attributes &attr) {
+    if (join_column == nullptr) {
+      return;
+    }
+    if (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Remove)) {
+      return;
+    }
+
+    delete_step_processor<CollectionType> processor{ctx_};
+    for (auto &obj : objects) {
+      if (!obj) {
+        continue;
+      }
+
+      auto result = processor.build(obj, true);
+      if (!result) {
+        throw query_builder_exception(result.release_error());
+      }
+    }
+  }
+
+  template<class CollectionType>
+  static void on_has_many(const char * /*id*/,
+                          object::collection<CollectionType> & /*objects*/,
+                          const char * /*join_column*/,
+                          const utils::foreign_attributes & /*attr*/) {
+    // Value-Collections bzw. Relationstabellen werden hier nicht direkt gelöscht.
+    // Dafür wird das Delete-Statement der jeweiligen Entity verwendet.
+  }
+
+  template<class ForeignType>
+  void on_has_many_to_many(const char *id,
+                           object::collection<object::object_ptr<ForeignType>> &objects,
+                           const char *join_column,
+                           const char *inverse_join_column,
+                           const utils::foreign_attributes &attr) {
+    if (id == nullptr || join_column == nullptr || inverse_join_column == nullptr) {
+      return;
+    }
+
+    using relation_value_type = object::many_to_many_relation<ObjectType, ForeignType>;
+    const std::type_index foreign_type{typeid(ForeignType)};
+    const std::type_index local_type{typeid(ObjectType)};
+    on_many_to_many_objects<relation_value_type>(
+      id,
+      objects,
+      attr,
+      [foreign_type, local_type](const char* relation_name) -> processing_many_to_many_key {
+        return {std::string{relation_name}, local_type, foreign_type};
+      });
+  }
+
+  template<class ForeignType>
+  void on_has_many_to_many(const char *id,
+                           object::collection<object::object_ptr<ForeignType>> &objects,
+                           const utils::foreign_attributes &attr) {
+    if (id == nullptr) {
+      return;
+    }
+
+    object::join_columns_collector collector;
+    if (auto join_columns = collector.collect<ForeignType>(); join_columns.join_column.empty() || join_columns.inverse_join_column.empty()) {
+      return;
+    }
+
+    using relation_value_type = object::many_to_many_relation<ForeignType, ObjectType>;
+    const std::type_index foreign_type{typeid(ForeignType)};
+    const std::type_index local_type{typeid(ObjectType)};
+    on_many_to_many_objects<relation_value_type>(
+      id,
+      objects,
+      attr,
+      [foreign_type, local_type](const char* relation_name) -> processing_many_to_many_key {
+         return {std::string{relation_name}, foreign_type, local_type};
+      });
+  }
+
+private:
+  template<class PointerType>
+  void on_foreign_object(object::object_ptr<PointerType> &obj, const utils::foreign_attributes &attr) {
+    if (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Remove) || !obj) {
+      return;
+    }
+
+    delete_step_processor<PointerType> processor{ctx_};
+
+    auto result = processor.build(obj);
+    if (!result) {
+      throw query_builder_exception(result.release_error());
+    }
+  }
+
+  template<class LocalType, class ForeignType, class RelationKeyFactory>
+  void on_many_to_many_objects(const char *id,
+                               object::collection<object::object_ptr<ForeignType>> &objects,
+                               const utils::foreign_attributes &attr,
+                               RelationKeyFactory make_relation_key) {
+    if (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Remove)) {
+      return;
+    }
+
+    const auto key = make_relation_key(id);
+    if (ctx_.processing_many_to_many_relations_.find(key) != ctx_.processing_many_to_many_relations_.end()) {
+      return;
+    }
+
+    const auto it = ctx_.schema_.find(std::string{id});
+    if (it == ctx_.schema_.end()) {
+      throw query_builder_exception(error_code::UnknownType, "Unknown type for relation " + std::string{id});
+    }
+
+    if (std::type_index(typeid(LocalType)) != it->second.node().info().type_index()) {
+      throw query_builder_exception(error_code::InvalidRelationType, "Invalid relation type for " + std::string{id});
+    }
+
+    if (const auto cit = ctx_.contexts_by_type_.find(it->second.node().info().type_index()); cit == ctx_.contexts_by_type_.end()) {
+      throw query_builder_exception(error_code::UnknownType, "No query contexts for type " + it->second.node().name());
+    }
+
+    std::ignore = ctx_.processing_many_to_many_relations_.insert(key);
+    std::vector<std::unique_ptr<execute_step>> delete_relation_steps;
+    delete_step_processor<ForeignType> processor{ctx_};
+    for (auto &obj : objects) {
+      if (!obj) {
+        continue;
+      }
+
+      if (obj.is_persistent()) {
+        auto result = processor.build(obj, true);
+        if (!result) {
+          throw query_builder_exception(result.release_error());
+        }
+      }
+    }
+  }
+
+private:
+  query_builder_context &ctx_;
+  object::object_ptr<ObjectType> ptr_;
+};
+
+template<class ObjectType>
+class delete_query_builder {
+public:
+  explicit delete_query_builder(const basic_schema &schema,
+                                const std::unordered_map<std::type_index, query_contexts> &contexts_by_type)
+  : schema_(schema)
+  , contexts_by_type_(contexts_by_type) {}
+
+  utils::result<std::vector<std::unique_ptr<execute_step>>, utils::error> build(const object::object_ptr<ObjectType> &ptr) {
+    if (const auto it = schema_.find(typeid(ObjectType)); it == schema_.end()) {
+      return utils::failure(utils::error{error_code::UnknownType, "Unknown type for delete query"});
+    }
+
+    query_builder_context ctx{schema_, contexts_by_type_};
+    delete_step_processor<ObjectType> processor{ctx};
+
+    const auto result = processor.build(ptr);
+    if (!result) {
+      return utils::failure(result.err());
+    }
+
+    // relation inserts must run after all entity inserts were collected
+    for (auto &s : ctx.steps_) {
+      ctx.relation_steps_.push_back(std::move(s));
+    }
+    ctx.steps_.clear();
+
+    return utils::ok(std::move(ctx.relation_steps_));
+  }
+
+private:
+  const basic_schema &schema_;
+  const std::unordered_map<std::type_index, query_contexts> &contexts_by_type_;
+};
+} // namespace matador::query
+
+#endif //MATADOR_DELETE_QUERY_BUILDER_HPP

include/matador/query/delete_step.hpp

@@ -0,0 +1,84 @@
+#ifndef MATADOR_DELETE_STEP_HPP
+#define MATADOR_DELETE_STEP_HPP
+
+#include "matador/query/error_code.hpp"
+#include "matador/query/execute_step.hpp"
+
+#include "matador/sql/internal/identifier_statement_binder.hpp"
+#include "matador/sql/statement.hpp"
+
+#include "matador/object/object_ptr.hpp"
+
+namespace matador::query {
+template<typename ObjectType>
+class delete_step_object final : public execute_step {
+public:
+  delete_step_object(sql::query_context ctx, const object::object_ptr<ObjectType> &ptr)
+  : execute_step(std::move(ctx))
+  , ptr_(ptr) {}
+
+  utils::result<void, utils::error> prepare(sql::executor &/*conn*/) override {
+    id_ = ptr_.primary_key();
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> execute(sql::statement &stmt) override {
+    if (!ptr_) {
+      return utils::failure(utils::error{error_code::InvalidObject, "Object is null"});
+    }
+
+    sql::identifier_statement_binder binder(stmt, 0);
+    binder.bind(id_);
+
+    if (const auto result = stmt.execute(); !result.is_ok()) {
+      return utils::failure(result.err());
+    }
+
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> finalize(object::object_cache &cache, const resolver_service_ptr& /*resolver_service*/) override {
+    if (!ptr_) {
+      return utils::failure(utils::error{error_code::InvalidObject, "Object is null"});
+    }
+
+    cache.erase<ObjectType>(id_);
+    ptr_.change_state(object::object_state::Transient);
+
+    return utils::ok<void>();
+  }
+
+private:
+  object::object_ptr<ObjectType> ptr_;
+};
+
+template <typename ObjectType>
+class delete_step_relation : public execute_step {
+public:
+  delete_step_relation(sql::query_context ctx, const object::object_ptr<ObjectType>& ptr)
+  : execute_step(std::move(ctx))
+  , ptr_(ptr) {}
+
+  utils::result<void, utils::error> prepare(sql::executor &) override {
+    return utils::ok<void>();
+  }
+  utils::result<void, utils::error> execute(sql::statement &stmt) override {
+    stmt.bind(*ptr_);
+    if (const auto exec_result = stmt.execute(); !exec_result.is_ok()) {
+      return utils::failure(exec_result.err());
+    }
+
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> finalize(object::object_cache& /*cache*/, const resolver_service_ptr& /*resolver_service*/) override {
+    return utils::ok<void>();
+  }
+
+private:
+  object::object_ptr<ObjectType> ptr_;
+};
+
+}
+
+#endif //MATADOR_DELETE_STEP_HPP

include/matador/query/dependency_collector.hpp

@@ -59,16 +59,18 @@ struct meta_registry {
 struct dependency_collector {
   std::vector<fk_ref> refs;
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template<class V>
-  static void on_primary_key(const char*, V&, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {}
+  static void on_primary_key(const char*, V&, const utils::primary_key_attribute& /*attr*/) {}
 
   static void on_revision(const char*, std::uint64_t&) {}
 
   template<class V>
-  static void on_attribute(const char*, V&, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char*, V&, const utils::field_attributes &/*attr*/) {}
 
   template<class Pointer>
-  void on_belongs_to(const char* id, Pointer& p, utils::foreign_attributes &attr) {
+  void on_belongs_to(const char* id, Pointer& p, utils::foreign_attributes &/*attr*/) {
     // Erwartung: Pointer verhält sich wie matador::object::object_ptr<T>
     // also: p.get() liefert raw ptr, und Pointer::value_type / element_type ist T.
     auto* raw = p.get();
@@ -87,16 +89,16 @@ struct dependency_collector {
   }
 
   template<class Pointer>
-  static void on_has_one(const char*, Pointer&, const auto&) {}
+  static void on_has_one(const char*, Pointer&, const char * /*join_column*/, const utils::foreign_attributes&) {}
 
   template<class Container>
-  static void on_has_many(const char*, Container&, const char*, const auto&) {}
+  static void on_has_many(const char*, Container&, const char*, const utils::foreign_attributes&) {}
 
   template<class Container>
-  static void on_has_many_to_many(const char*, Container&, const char*, const char*, const auto&) {}
+  static void on_has_many_to_many(const char*, Container&, const char*, const char*, const utils::foreign_attributes&) {}
 
   template<class Container>
-  static void on_has_many_to_many(const char*, Container&, const auto&) {}
+  static void on_has_many_to_many(const char*, Container&, const utils::foreign_attributes&) {}
 };
 
 struct flush_node {

include/matador/query/error_code.hpp

@@ -0,0 +1,46 @@
+#ifndef MATADOR_ERROR_CODE_HPP
+#define MATADOR_ERROR_CODE_HPP
+
+#include <cstdint>
+#include <system_error>
+
+namespace matador::query {
+enum class error_code {
+  Ok,
+  Failure,
+  InvalidQuery,
+  InvalidSchema,
+  InvalidTable,
+  InvalidColumn,
+  InvalidConstraint,
+  InvalidDataType,
+  InvalidObject,
+  InvalidValue,
+  InvalidRelationType,
+  MissingPrimaryKey,
+  UnknownType,
+  FailedToAcquireConnection,
+  FailedToFindPrimaryKey,
+  FailedToBuildQuery,
+  FailedToFindObject,
+  FailedToInsertObject,
+  FailedToAcquirePool,
+  UnexpectedError
+};
+
+class query_category_impl final : public std::error_category
+{
+public:
+    [[nodiscard]] const char* name() const noexcept override;
+    [[nodiscard]] std::string message(int ev) const override;
+};
+
+const std::error_category& query_category();
+std::error_code make_error_code(error_code e);
+std::error_condition make_error_condition(error_code e);
+
+}
+
+template <>
+struct std::is_error_code_enum<matador::query::error_code> : true_type {};
+#endif //MATADOR_ERROR_CODE_HPP

include/matador/query/execute_step.hpp

@@ -0,0 +1,37 @@
+#ifndef MATADOR_EXECUTE_STEP_HPP
+#define MATADOR_EXECUTE_STEP_HPP
+
+#include "matador/utils/identifier.hpp"
+#include "matador/utils/primary_key_accessor.hpp"
+#include "matador/utils/error.hpp"
+#include "matador/utils/result.hpp"
+
+#include "matador/object/object_cache.hpp"
+
+#include "matador/sql/query_context.hpp"
+#include "matador/sql/executor.hpp"
+
+#include "matador/query/abstract_pk_generator.hpp"
+
+namespace matador::query {
+using resolver_service_ptr = std::shared_ptr<sql::resolver_service>;
+
+class execute_step {
+public:
+  explicit execute_step(sql::query_context ctx)
+  : ctx_(std::move(ctx)) {}
+  virtual ~execute_step() = default;
+
+  virtual utils::result<void, utils::error> prepare(sql::executor &conn) = 0;
+  virtual utils::result<void, utils::error> execute(sql::statement &stmt) = 0;
+  virtual utils::result<void, utils::error> finalize(object::object_cache& cache, const resolver_service_ptr& resolver_service) = 0;
+
+  [[nodiscard]] const sql::query_context& ctx() const { return ctx_; }
+
+protected:
+  utils::identifier id_;
+  utils::primary_key_accessor pk_accessor_;
+  sql::query_context ctx_;
+};
+}
+#endif //MATADOR_EXECUTE_STEP_HPP

include/matador/query/expression/abstract_column_expression.hpp

@@ -0,0 +1,18 @@
+#ifndef MATADOR_ABSTRACT_COLUMN_EXPRESSION_HPP
+#define MATADOR_ABSTRACT_COLUMN_EXPRESSION_HPP
+
+#include <memory>
+
+namespace matador::query {
+class expression_visitor;
+class table_column;
+class abstract_column_expression {
+public:
+    virtual ~abstract_column_expression() = default;
+
+    virtual void accept(expression_visitor& visitor) const = 0;
+};
+
+using column_expression_ptr = std::unique_ptr<abstract_column_expression>;
+}
+#endif //MATADOR_ABSTRACT_COLUMN_EXPRESSION_HPP

include/matador/query/expression/binary_column_expression.hpp

@@ -0,0 +1,31 @@
+#ifndef MATADOR_BINARY_COLUMN_EXPRESSION_HPP
+#define MATADOR_BINARY_COLUMN_EXPRESSION_HPP
+
+#include "matador/query/expression/abstract_column_expression.hpp"
+
+namespace matador::query {
+enum class binary_expression_operator {
+  Plus,
+  Minus,
+  Multiply,
+  Divide,
+  Modulo
+};
+
+class binary_column_expression : public abstract_column_expression {
+public:
+  binary_column_expression() = delete;
+  binary_column_expression(column_expression_ptr left_column, binary_expression_operator operand, column_expression_ptr right_column);
+
+  void accept(expression_visitor& visitor) const override;
+
+  [[nodiscard]] const column_expression_ptr& left_column() const;
+  [[nodiscard]] binary_expression_operator operand() const;
+  [[nodiscard]] const column_expression_ptr& right_column() const;
+private:
+  column_expression_ptr left_column_;
+  binary_expression_operator operand_;
+  column_expression_ptr right_column_;
+};
+}
+#endif //MATADOR_BINARY_COLUMN_EXPRESSION_HPP

include/matador/query/expression/column_expression.hpp

@@ -0,0 +1,55 @@
+#ifndef MATADOR_COLUMN_EXPRESSION_HPP
+#define MATADOR_COLUMN_EXPRESSION_HPP
+
+#include "matador/query/expression/table_column_expression.hpp"
+#include "matador/query/expression/value_expression.hpp"
+#include "matador/query/expression/placeholder_expression.hpp"
+
+#include "matador/utils/placeholder.hpp"
+#include "matador/utils/types.hpp"
+
+namespace matador::query {
+class column_expression {
+public:
+    column_expression() = default;
+    explicit column_expression(column_expression_ptr expr) noexcept;
+
+    template<typename Type, typename = std::enable_if_t<std::is_convertible_v<Type, utils::database_type>>>
+    column_expression(Type&& value)
+    : column_expression(std::make_unique<value_expression>(std::forward<Type>(value))){
+    }
+    column_expression(utils::placeholder p);
+    column_expression(const column_expression&) = delete;
+    column_expression& operator=(const column_expression&) = delete;
+    column_expression(column_expression&&) noexcept = default;
+    column_expression& operator=(column_expression&&) noexcept = default;
+
+    [[nodiscard]] bool empty() const noexcept;
+    [[nodiscard]] const abstract_column_expression* get() const noexcept;
+    [[nodiscard]] const column_expression_ptr& ptr() const noexcept;
+    column_expression_ptr release() noexcept;
+
+    // Move out for APIs that still take column_expression_ptr
+    operator column_expression_ptr() && noexcept;
+
+    // The feature you want: turn an expression into a SELECT-able column with alias
+    [[nodiscard]] table_column as(const std::string& alias) &&;
+
+private:
+    column_expression_ptr expression_{};
+};
+
+// Helper constructors (optional but convenient)
+inline column_expression make_column_expression(const table_column& col) {
+    return column_expression{std::make_unique<table_column_expression>(col)};
+}
+
+inline column_expression make_column_expression(utils::database_type v) {
+    return column_expression{std::make_unique<value_expression>(std::move(v))};
+}
+
+inline column_expression make_column_expression(utils::placeholder) {
+    return column_expression{std::make_unique<placeholder_expression>()};
+}
+}
+#endif //MATADOR_COLUMN_EXPRESSION_HPP

include/matador/query/expression/expression_operators.hpp

@@ -0,0 +1,118 @@
+#ifndef MATADOR_EXPRESSION_OPERATORS_HPP
+#define MATADOR_EXPRESSION_OPERATORS_HPP
+
+#include "matador/query/expression/binary_column_expression.hpp"
+#include "matador/query/expression/table_column_expression.hpp"
+#include "matador/query/expression/value_expression.hpp"
+#include "matador/query/expression/column_expression.hpp"
+
+#include "matador/utils/placeholder.hpp"
+
+namespace matador::query {
+template<typename Type>
+column_expression operator+(const table_column& col, Type&& val) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<table_column_expression>(col),
+    binary_expression_operator::Plus,
+    std::make_unique<value_expression>(std::forward<Type>(val))
+)};
+}
+
+template<typename Type>
+column_expression operator+(Type&& val, const table_column& col) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<value_expression>(std::forward<Type>(val)),
+    binary_expression_operator::Plus,
+    std::make_unique<table_column_expression>(col)
+  )};
+}
+
+column_expression operator+(const table_column& col, utils::placeholder /*val*/);
+column_expression operator+(utils::placeholder /*val*/, const table_column& col);
+
+template<typename Type>
+column_expression operator-(const table_column& col, Type&& val) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<table_column_expression>(col),
+    binary_expression_operator::Minus,
+    std::make_unique<value_expression>(std::forward<Type>(val))
+  )};
+}
+
+template<typename Type>
+column_expression operator-(Type&& val, const table_column& col) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<value_expression>(std::forward<Type>(val)),
+    binary_expression_operator::Minus,
+    std::make_unique<table_column_expression>(col)
+  )};
+}
+
+column_expression operator-(const table_column& col, utils::placeholder /*val*/);
+column_expression operator-(utils::placeholder /*val*/, const table_column& col);
+
+template<typename Type>
+column_expression operator*(const table_column& col, Type&& val) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<table_column_expression>(col),
+    binary_expression_operator::Multiply,
+    std::make_unique<value_expression>(std::forward<Type>(val))
+  )};
+}
+
+template<typename Type>
+column_expression operator*(Type&& val, const table_column& col) {
+  return std::make_unique<binary_column_expression>(
+    std::make_unique<value_expression>(std::forward<Type>(val)),
+    binary_expression_operator::Multiply,
+    std::make_unique<table_column_expression>(col)
+);
+}
+
+column_expression operator*(const table_column& col, utils::placeholder /*val*/);
+column_expression operator*(utils::placeholder /*val*/, const table_column& col);
+column_expression operator*(column_expression&& left, column_expression&& right);
+
+template<typename Type>
+column_expression operator/(const table_column& col, Type&& val) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<table_column_expression>(col),
+    binary_expression_operator::Divide,
+    std::make_unique<value_expression>(std::forward<Type>(val))
+  )};
+}
+
+template<typename Type>
+column_expression operator/(Type&& val, const table_column& col) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<value_expression>(std::forward<Type>(val)),
+    binary_expression_operator::Divide,
+    std::make_unique<table_column_expression>(col)
+  )};
+}
+
+column_expression operator/(const table_column& col, utils::placeholder /*val*/);
+column_expression operator/(utils::placeholder /*val*/, const table_column& col);
+
+template<typename Type>
+column_expression operator%(const table_column& col, Type&& val) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<table_column_expression>(col),
+    binary_expression_operator::Modulo,
+    std::make_unique<value_expression>(std::forward<Type>(val))
+  )};
+}
+
+template<typename Type>
+column_expression operator%(Type&& val, const table_column& col) {
+  return column_expression{std::make_unique<binary_column_expression>(
+    std::make_unique<value_expression>(std::forward<Type>(val)),
+    binary_expression_operator::Modulo,
+    std::make_unique<table_column_expression>(col)
+  )};
+}
+
+column_expression operator%(const table_column& col, utils::placeholder /*val*/);
+column_expression operator%(utils::placeholder /*val*/, const table_column& col);
+}
+#endif //MATADOR_EXPRESSION_OPERATORS_HPP

include/matador/query/expression/expression_visitor.hpp

@@ -0,0 +1,20 @@
+#ifndef MATADOR_EXPRESSION_VISITOR_HPP
+#define MATADOR_EXPRESSION_VISITOR_HPP
+
+namespace matador::query {
+class binary_column_expression;
+class table_column_expression;
+class value_expression;
+class placeholder_expression;
+
+class expression_visitor {
+public:
+  virtual ~expression_visitor() = default;
+
+  virtual void visit(const binary_column_expression& node) = 0;
+  virtual void visit(const table_column_expression& node) = 0;
+  virtual void visit(const value_expression& node) = 0;
+  virtual void visit(const placeholder_expression& node) = 0;
+};
+}
+#endif //MATADOR_EXPRESSION_VISITOR_HPP

include/matador/query/expression/placeholder_expression.hpp

@@ -0,0 +1,14 @@
+#ifndef MATADOR_PLACEHOLDER_EXPRESSION_HPP
+#define MATADOR_PLACEHOLDER_EXPRESSION_HPP
+
+#include "matador/query/expression/abstract_column_expression.hpp"
+
+namespace matador::query {
+class placeholder_expression : public abstract_column_expression {
+public:
+  placeholder_expression() = default;
+
+  void accept(expression_visitor& visitor) const override;
+};
+}
+#endif //MATADOR_PLACEHOLDER_EXPRESSION_HPP

include/matador/query/expression/table_column_expression.hpp

@@ -0,0 +1,21 @@
+#ifndef MATADOR_TABLE_COLUMN_EXPRESSION_HPP
+#define MATADOR_TABLE_COLUMN_EXPRESSION_HPP
+
+#include "matador/query/expression/abstract_column_expression.hpp"
+#include "matador/query/table_column.hpp"
+
+namespace matador::query {
+class table_column_expression : public abstract_column_expression {
+public:
+  table_column_expression() = delete;
+  explicit table_column_expression(table_column col);
+
+  void accept(expression_visitor& visitor) const override;
+
+  [[nodiscard]] const table_column& col() const;
+
+private:
+  table_column column_;
+};
+}
+#endif //MATADOR_TABLE_COLUMN_EXPRESSION_HPP

include/matador/query/expression/value_expression.hpp

@@ -0,0 +1,22 @@
+#ifndef MATADOR_VALUE_EXPRESSION_HPP
+#define MATADOR_VALUE_EXPRESSION_HPP
+
+#include "matador/query/expression/abstract_column_expression.hpp"
+
+#include "matador/utils/types.hpp"
+
+namespace matador::query {
+class value_expression : public abstract_column_expression {
+public:
+  value_expression() = delete;
+  explicit value_expression(utils::database_type value);
+
+  void accept(expression_visitor& visitor) const override;
+
+  [[nodiscard]] const utils::database_type& value() const;
+
+private:
+  utils::database_type value_;
+};
+}
+#endif //MATADOR_VALUE_EXPRESSION_HPP

include/matador/query/expression_evaluator.hpp

@@ -0,0 +1,30 @@
+#ifndef MATADOR_EXPRESSION_EVALUATOR_HPP
+#define MATADOR_EXPRESSION_EVALUATOR_HPP
+
+#include "matador/query/expression/expression_visitor.hpp"
+
+#include <string>
+
+namespace matador::sql {
+class dialect;
+struct query_context;
+}
+
+namespace matador::query {
+class expression_evaluator final : public expression_visitor {
+public:
+    expression_evaluator(const sql::dialect &d, sql::query_context &query);
+    void visit(const binary_column_expression& node) override;
+    void visit(const table_column_expression& node) override;
+    void visit(const value_expression& node) override;
+    void visit(const placeholder_expression& node) override;
+
+    [[nodiscard]] const std::string& result() const;
+
+private:
+    const sql::dialect &dialect_;
+    sql::query_context &query_;
+    std::string expression_;
+};
+}
+#endif //MATADOR_EXPRESSION_EVALUATOR_HPP

include/matador/query/fk_value_extractor.hpp

@@ -12,30 +12,30 @@ class foreign_attributes;
 
 namespace matador::query::detail {
 
-class fk_value_extractor
+class fk_value_extractor {
-{
 public:
   fk_value_extractor() = default;
 
   template<class Type>
-  utils::database_type extract(Type &x)
+  utils::database_type extract(Type &x) {
-  {
     access::process(*this, x);
     return value_;
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template<typename ValueType>
-  void on_primary_key(const char *, ValueType &pk, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {
+  void on_primary_key(const char *, ValueType &pk, const utils::primary_key_attribute& /*attr*/) {
     value_ = pk;
   }
   static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
   template < class Type >
-  static void on_attribute(const char * /*id*/, Type &/*x*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, Type &/*x*/, const utils::field_attributes &/*attr*/) {}
-  static void on_attribute(const char * /*id*/, char * /*x*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, char * /*x*/, const utils::field_attributes &/*attr*/) {}
   template<class Pointer>
   static void on_belongs_to(const char * /*id*/, Pointer &/*x*/, const utils::foreign_attributes &/*attr*/) {}
   template<class Pointer>
-  static void on_has_one(const char * /*id*/, Pointer &/*x*/, const utils::foreign_attributes &/*attr*/) {}
+  static void on_has_one(const char * /*id*/, Pointer &/*x*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {}
   template<class ContainerType>
   static void on_has_many_to_many(const char *, ContainerType &, const char * /*join_column*/, const char * /*inverse_join_column*/, const utils::foreign_attributes &/*attr*/) {}
   template<class ContainerType>

include/matador/query/generator.hpp

@@ -63,14 +63,16 @@ public:
     return result_;
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template < class V >
-  void on_primary_key(const char *id, V &, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {
+  void on_primary_key(const char *id, V &, const utils::primary_key_attribute& /*attr*/) {
       push(id);
   }
   void on_revision(const char *id, uint64_t &/*rev*/);
 
   template<typename Type>
-  void on_attribute(const char *id, Type &, const utils::field_attributes &/*attr*/ = utils::null_attributes) {
+  void on_attribute(const char *id, Type &, const utils::field_attributes &/*attr*/) {
       push(id);
   }
 
@@ -79,7 +81,7 @@ public:
     on_foreign_key(id, x, attr);
   }
   template<class Pointer>
-  void on_has_one(const char *id, Pointer &x, const utils::foreign_attributes &attr) {
+  void on_has_one(const char *id, Pointer &x, const char * /*join_column*/, const utils::foreign_attributes &attr) {
     on_foreign_key(id, x, attr);
   }
 
@@ -105,7 +107,7 @@ public:
   }
 
   template<class CollectionType>
-  void on_has_many(const char * /*id*/, CollectionType &, const char *join_column, const utils::foreign_attributes &attr, std::enable_if_t<!object::is_object_ptr<typename CollectionType::value_type>::value> * = nullptr) {
+  void on_has_many(const char * /*id*/, CollectionType &, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/, std::enable_if_t<!object::is_object_ptr<typename CollectionType::value_type>::value> * = nullptr) {
   }
 
   template<class ContainerType>
@@ -169,14 +171,16 @@ public:
     return result_;
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template < class V >
-  void on_primary_key(const char * /*id*/, V &/*x*/, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {
+  void on_primary_key(const char * /*id*/, V &/*x*/, const utils::primary_key_attribute& /*attr*/) {
     result_.emplace_back(utils::_);
   }
   void on_revision(const char *id, uint64_t &/*rev*/);
 
   template<typename Type>
-  void on_attribute(const char * /*id*/, Type &/*x*/, const utils::field_attributes &/*attr*/ = utils::null_attributes) {
+  void on_attribute(const char * /*id*/, Type &/*x*/, const utils::field_attributes &/*attr*/) {
     result_.emplace_back(utils::_);
   }
 
@@ -185,7 +189,7 @@ public:
     result_.emplace_back(utils::_);
   }
   template<class Type, template < class ... > class Pointer>
-  void on_has_one(const char * /*id*/, Pointer<Type> &/*x*/, const utils::foreign_attributes &/*attr*/) {
+  void on_has_one(const char * /*id*/, Pointer<Type> &/*x*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {
     result_.emplace_back(utils::_);
   }
   template<class ContainerType>
@@ -224,17 +228,19 @@ public:
       result_.clear();
       access::process(*this, obj);
 
-      return result_;
+      return std::move(result_);
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template < class V >
-  void on_primary_key(const char *id, V &x, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {
+  void on_primary_key(const char *id, V &x, const utils::primary_key_attribute& /*attr*/) {
     push_back(id, x);
   }
   void on_revision(const char *id, uint64_t &/*rev*/);
 
   template<typename Type>
-  void on_attribute(const char *id, Type &x, const utils::field_attributes &/*attr*/ = utils::null_attributes) {
+  void on_attribute(const char *id, Type &x, const utils::field_attributes &/*attr*/) {
     push_back(id, x);
   }
 
@@ -243,7 +249,7 @@ public:
     push_back(id, fk_value_extractor_.extract(*x));
   }
   template<class Type, template < class ... > class Pointer>
-  void on_has_one(const char *id, Pointer<Type> &x, const utils::foreign_attributes &/*attr*/) {
+  void on_has_one(const char *id, Pointer<Type> &x, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {
     push_back(id, fk_value_extractor_.extract(*x));
   }
   template<class ContainerType>
@@ -256,9 +262,9 @@ public:
   template<typename Type>
   void push_back(const char* id, const Type& value) {
     if (is_column_value_generator_option_set(options_, column_value_generator_options::ValuesAsPlaceHolder)) {
-      result_.emplace_back(id, utils::_);
+      result_.emplace_back(id, std::make_unique<placeholder_expression>());
     } else {
-      result_.emplace_back(id, value);
+      result_.emplace_back(id, std::make_unique<value_expression>(value));
     }
   }
 
@@ -280,6 +286,8 @@ std::vector<utils::placeholder> placeholders(const Type &obj) {
   return generator.generate(obj);
 }
 
+std::vector<utils::placeholder> placeholders(size_t num);
+
 template<typename Type>
 std::vector<internal::column_value_pair> column_value_pairs(const Type &obj, const column_value_generator_options options = column_value_generator_options::None) {
   column_value_generator generator(options);

include/matador/query/identity_pk_generator.hpp

@@ -0,0 +1,14 @@
+#ifndef MATADOR_IDENTITY_PK_GENERATOR_HPP
+#define MATADOR_IDENTITY_PK_GENERATOR_HPP
+
+#include "matador/query/abstract_pk_generator.hpp"
+
+namespace matador::query {
+class identity_pk_generator : public abstract_pk_generator {
+public:
+  identity_pk_generator();
+  [[nodiscard]] utils::result<int64_t, utils::error> next_id(const sql::executor& exec) override;
+  [[nodiscard]] utils::result<int64_t, utils::error> current_id(const sql::executor& exec) override;
+};
+}
+#endif //MATADOR_IDENTITY_PK_GENERATOR_HPP

include/matador/query/insert_query_builder.hpp

@@ -1,133 +1,119 @@
 #ifndef MATADOR_INSERT_QUERY_BUILDER_HPP
 #define MATADOR_INSERT_QUERY_BUILDER_HPP
 
+#include "matador/object/collection.hpp"
+#include "matador/object/object_ptr.hpp"
+
 #include "matador/query/basic_schema.hpp"
 #include "matador/query/intermediates/executable_query.hpp"
+#include "matador/query/insert_step.hpp"
 #include "matador/query/query.hpp"
+#include "matador/query/query_contexts.hpp"
 #include "matador/query/query_builder_exception.hpp"
+#include "matador/query/query_builder_utils.hpp"
+
+#include "matador/sql/statement.hpp"
+
+#include "matador/utils/primary_key_accessor.hpp"
+
+namespace matador::sql {
+class statement_cache;
+}
 
 namespace matador::query {
-
+template < class ObjectType >
-struct pk_setter {
+class has_many_linker {
-  const std::string &name;
-  std::uint64_t value;
-
-  template<class V>
-  void on_primary_key(const char *id, V &pk, const utils::primary_key_attribute & = utils::default_pk_attributes) {
-    if (id != nullptr && name == id) {
-      pk = static_cast<V>(value);
-    }
-  }
-  static void on_revision(const char * /*id*/, uint64_t & /*rev*/) {}
-  template<typename T>
-  static void on_attribute(const char * /*id*/, T &, const utils::field_attributes & = utils::null_attributes) {}
-  template<class P>
-  static void on_belongs_to(const char * /*id*/, P &, const utils::foreign_attributes & ) {}
-  template<class P>
-  static void on_has_one(const char * /*id*/, P &, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many(const char * /*id*/, C &, const char * /*join_column*/, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many_to_many(const char * /*id*/, C &, const char * /*join_column*/, const char * /*inverse_join_column*/, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many_to_many(const char * /*id*/, C &, const utils::foreign_attributes & ) {}
-};
-
-struct pk_unset_checker {
-  const std::string &name;
-  bool unset{true};
-
-  template<class V>
-  void on_primary_key(const char *id, V &pk, const utils::primary_key_attribute & = utils::default_pk_attributes) {
-    if (id != nullptr && name == id) {
-      // Your convention: 0 means unset for integer PKs
-      unset = (static_cast<std::uint64_t>(pk) == 0ULL);
-    }
-  }
-  static void on_revision(const char * /*id*/, uint64_t & /*rev*/) {}
-  template<typename T>
-  static void on_attribute(const char * /*id*/, T &, const utils::field_attributes & = utils::null_attributes) {}
-  template<class P>
-  static void on_belongs_to(const char * /*id*/, P &, const utils::foreign_attributes & ) {}
-  template<class P>
-  static void on_has_one(const char * /*id*/, P &, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many(const char * /*id*/, C &, const char * /*join_column*/, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many_to_many(const char * /*id*/, C &, const char * /*join_column*/, const char * /*inverse_join_column*/, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many_to_many(const char * /*id*/, C &, const utils::foreign_attributes & ) {}
-};
-
-struct pk_value_extractor {
-  std::uint64_t value{0};
-
-  template<class V>
-  void on_primary_key(const char * /*id*/, V &pk, const utils::primary_key_attribute & = utils::default_pk_attributes) {
-    value = static_cast<std::uint64_t>(pk);
-  }
-  static void on_revision(const char * /*id*/, uint64_t & /*rev*/) {}
-  template<typename T>
-  static void on_attribute(const char * /*id*/, T &, const utils::field_attributes & = utils::null_attributes) {}
-  template<class P>
-  static void on_belongs_to(const char * /*id*/, P &, const utils::foreign_attributes & ) {}
-  template<class P>
-  static void on_has_one(const char * /*id*/, P &, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many(const char * /*id*/, C &, const char * /*join_column*/, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many_to_many(const char * /*id*/, C &, const char * /*join_column*/, const char * /*inverse_join_column*/, const utils::foreign_attributes & ) {}
-  template<class C>
-  static void on_has_many_to_many(const char * /*id*/, C &, const utils::foreign_attributes & ) {}
-};
-
-class insert_query_builder {
 public:
-  using step_query_t = std::variant<executable_query, fetchable_query>;
+  has_many_linker(const object::object_ptr<ObjectType> &ptr, std::string join_column)
-
+  : ptr_(ptr), join_column_(std::move(join_column)) {}
-  struct insert_step {
+  template<typename BaseType>
-    step_query_t query;
+  static void on_base(const BaseType&) {}
-
+  template < class PrimaryKeyType >
-    // Session uses these to handle manual/sequence/table pre-insert PKs
+  static void on_primary_key(const char * /*id*/, PrimaryKeyType &, const utils::primary_key_attribute& /*attr*/) {}
-    utils::generator_type pk_generator{utils::generator_type::Manually};
+  static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
-    std::string pk_name;
-
-    std::function<bool()> pk_is_unset{};
-    std::function<void(std::uint64_t)> set_pk{};
-
-    // Identity post-insert
-    std::function<void(const sql::record &)> apply_returning{};
-  };
-
-public:
-  explicit insert_query_builder(const basic_schema &schema);
-
-  template<class EntityType>
-  utils::result<std::vector<insert_step>, query_build_error> build(const object::object_ptr<EntityType> &ptr) {
-    if (const auto it = schema_.find(typeid(EntityType)); it == schema_.end()) {
-      return utils::failure(query_build_error::UnknownType);
-    }
-
-    steps_.clear();
-    visited_.clear();
-
-    build_for(ptr);
-
-    // relation inserts must run after all entity inserts were collected
-    for (auto &s : relation_steps_) {
-      steps_.push_back(std::move(s));
-    }
-    relation_steps_.clear();
-
-    return utils::ok(steps_);
-  }
-
-  template < class V >
-  static void on_primary_key(const char * /*id*/, V &, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {}
-  static void on_revision(const char *id, uint64_t &/*rev*/);
-
   template<typename Type>
-  static void on_attribute(const char * /*id*/, Type &, const utils::field_attributes &/*attr*/ = utils::null_attributes) {}
+  static void on_attribute(const char * /*id*/, Type &, const utils::field_attributes &/*attr*/) {}
+  template<class Pointer>
+  static void on_belongs_to(const char * /*id*/, Pointer &/*obj*/, const utils::foreign_attributes &/*attr*/) {}
+  void on_belongs_to(const char *id, object::object_ptr<ObjectType> &obj, const utils::foreign_attributes &/*attr*/) {
+    if (id != join_column_) {
+      return;
+    }
+
+    obj = ptr_;
+  }
+  template<class Pointer>
+  static void on_has_one(const char * /*id*/, Pointer &/*obj*/, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {}
+  template<class CollectionType>
+  static void on_has_many(const char * /*id*/, CollectionType &/*con*/, const char *, const utils::foreign_attributes &/*attr*/, std::enable_if_t<!object::is_object_ptr<typename CollectionType::value_type>::value> * = nullptr) {}
+  template<class Collection>
+  static void on_has_many_to_many(const char * /*id*/, Collection &/*container*/, const char * /*join_column*/, const char * /*inverse_join_column*/, const utils::foreign_attributes & ) {}
+  template<class Collection>
+  static void on_has_many_to_many(const char * /*id*/, Collection &/*container*/, const utils::foreign_attributes & ) {}
+
+private:
+  object::object_ptr<ObjectType> ptr_;
+  std::string join_column_;
+};
+
+template < typename ObjectType >
+class insert_step_processor {
+public:
+  explicit insert_step_processor(query_builder_context &ctx)
+  : ctx_{ctx}
+  {}
+
+  utils::result<void, utils::error> build(object::object_ptr<ObjectType> ptr, const bool as_relation_step = false) {
+    if (!ptr) {
+      return utils::failure(utils::error{error_code::InvalidObject, "Object is null"});
+    }
+    ptr_ = ptr;
+
+    const auto key = make_entity_visit_key<ObjectType>(*ptr_);
+    if (ctx_.visited_.find(key) != ctx_.visited_.end()) {
+      return utils::ok<void>();
+    }
+    ctx_.visited_.insert(key);
+
+    const auto it = ctx_.schema_.find(typeid(ObjectType));
+    if (it == ctx_.schema_.end()) {
+      return utils::failure(utils::error{error_code::UnknownType, "Unknown type"});
+    }
+
+    // 1) Traverse relations first => dependencies will be inserted before this object
+    try {
+      access::process(*this, *ptr_);
+    } catch (const query_builder_exception &ex) {
+      return utils::failure(ex.error());
+    }
+
+    // 2) Build INSERT for this object
+    const auto &info = it->second.node().info();
+    if (!info.has_primary_key() || it->second.pk_generator().type() == utils::generator_type::None) {
+      return utils::failure(utils::error{error_code::MissingPrimaryKey, "Type " + info.name() + " has no primary key"});
+    }
+    const auto cit = ctx_.contexts_by_type_.find(it->second.node().info().type_index());
+    if (cit == ctx_.contexts_by_type_.end()) {
+      return utils::failure(utils::error{error_code::UnknownType, "Unknown type"});
+    }
+
+    auto step = create_insert_step(cit->second.insert, it->second);
+    if (as_relation_step) {
+      ctx_.relation_steps_.push_back(std::move(step));
+    } else {
+      ctx_.steps_.push_back(std::move(step));
+    }
+
+    ptr_.reset();
+
+    return utils::ok<void>();
+  }
+
+  template < class PrimaryKeyType >
+  static void on_primary_key(const char * /*id*/, PrimaryKeyType &, const utils::primary_key_attribute& /*attr*/) {}
+  static void on_revision(const char * /*id*/, uint64_t &/*rev*/) {}
+  template<typename Type>
+  static void on_attribute(const char * /*id*/, Type &, const utils::field_attributes &/*attr*/) {}
 
   template<class Pointer>
   void on_belongs_to(const char * /*id*/, Pointer &obj, const utils::foreign_attributes &attr) {
@@ -135,150 +121,246 @@ public:
   }
 
   template<class Pointer>
-  void on_has_one(const char * /*id*/, Pointer &obj, const utils::foreign_attributes &attr) {
+  void on_has_one(const char * /*id*/, Pointer &obj, const char * /*join_column*/, const utils::foreign_attributes &attr) {
     on_foreign_object(obj, attr);
   }
-  template<class Collection>
+
-  static void on_has_many(const char * /*id*/, Collection &con, const char * /*join_column*/, const utils::foreign_attributes & ) {}
+  template<class CollectionType>
-  template<class Collection>
+  void on_has_many(const char * /*id*/,
-  void on_has_many_to_many(const char *id, Collection &con, const char *join_column, const char *inverse_join_column, const utils::foreign_attributes & ) {
+                   object::collection<object::object_ptr<CollectionType>> &objects,
-    if (id == nullptr || join_column == nullptr || inverse_join_column == nullptr) {
+                   const char *join_column,
+                   const utils::foreign_attributes &attr) {
+    if (join_column == nullptr) {
       return;
     }
-    if (current_entity_pk_ == 0ULL) {
+    if (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Insert)) {
-      // Without a local PK we cannot create relation rows
-      // (PK may be assigned later by Identity; that case needs a different mechanism than requested here)
       return;
     }
 
-    const auto rel_it = schema_.find(std::string{id});
+    has_many_linker<ObjectType> linker(ptr_, join_column);
-    if (rel_it == schema_.end()) {
+    insert_step_processor<CollectionType> processor{ctx_};
-      throw query_builder_exception(query_build_error::UnknownType);
+    for (auto &obj : objects) {
-    }
-    const table &rel_table = rel_it->second.table();
-
-    for (auto &obj : con) {
       if (!obj) {
         continue;
       }
 
-      // Ensure target exists as dependency (deps first)
+      if (obj.is_transient()) {
-      if (!obj.is_persistent()) {
+        auto result = processor.build(obj, true);
-        using dep_t = std::remove_reference_t<decltype(*obj)>;
+        if (!result) {
-        build_for<dep_t>(obj);
+          throw query_builder_exception(result.release_error());
+        }
       }
 
-      // Extract FK value from the foreign object
+      access::process(linker, *obj);
-      pk_value_extractor fk{};
+    }
-      access::process(fk, *obj);
+  }
-      if (fk.value == 0ULL) {
+
+  template<class CollectionType>
+  void on_has_many(const char *id,
+                   object::collection<CollectionType> &objects,
+                   const char *join_column,
+                   const utils::foreign_attributes &attr) {
+    if (id == nullptr || join_column == nullptr) {
+      return;
+    }
+    if (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Insert)) {
+      return;
+    }
+
+    const auto it = ctx_.schema_.find(std::string{id});
+    if (it == ctx_.schema_.end()) {
+      throw query_builder_exception(error_code::UnknownType, "Unknown type " + std::string{id});
+    }
+
+    using relation_value_type = object::many_to_relation<ObjectType, CollectionType>;
+    if (std::type_index(typeid(relation_value_type)) != it->second.node().info().type_index()) {
+      throw query_builder_exception(error_code::InvalidRelationType, "Invalid relation type");
+    }
+
+    const auto cit = ctx_.contexts_by_type_.find(it->second.node().info().type_index());
+    if (cit == ctx_.contexts_by_type_.end()) {
+      throw query_builder_exception(error_code::UnknownType, "Unknown type" + std::string{id});
+    }
+
+    for (auto &obj : objects) {
+      auto rel = object::make_object<relation_value_type>(join_column, "value", ptr_, obj);
+
+      ctx_.relation_steps_.push_back(std::make_unique<insert_step_relation<relation_value_type>>(cit->second.insert, rel));
+    }
+  }
+
+    template<class ForeignType>
+    void on_has_many_to_many(const char *id,
+                             object::collection<object::object_ptr<ForeignType>> &objects,
+                             const char *join_column,
+                             const char *inverse_join_column,
+                             const utils::foreign_attributes &attr) {
+    if (id == nullptr || join_column == nullptr || inverse_join_column == nullptr) {
+      return;
+    }
+
+    using relation_value_type = object::many_to_many_relation<ObjectType, ForeignType>;
+    const std::type_index foreign_type{typeid(ForeignType)};
+    const std::type_index local_type{typeid(ObjectType)};
+    insert_many_to_many_relations<relation_value_type>(
+      id,
+      objects,
+      attr,
+      [foreign_type, local_type](const char* relation_name) -> processing_many_to_many_key {
+        return {std::string{relation_name}, local_type, foreign_type};
+      },
+      [this, join_column, inverse_join_column](const auto &obj) {
+        return object::make_object<relation_value_type>(join_column, inverse_join_column, ptr_, obj);
+      });
+  }
+
+  template<class ForeignType>
+  void on_has_many_to_many(const char *id, object::collection<object::object_ptr<ForeignType>> &objects, const utils::foreign_attributes &attr) {
+    if (id == nullptr) {
+      return;
+    }
+
+    object::join_columns_collector collector;
+    auto join_columns = collector.collect<ForeignType>();
+    if (join_columns.join_column.empty() || join_columns.inverse_join_column.empty()) {
+      return;
+    }
+
+    using relation_value_type = object::many_to_many_relation<ForeignType, ObjectType>;
+    const std::type_index foreign_type{typeid(ForeignType)};
+    const std::type_index local_type{typeid(ObjectType)};
+    insert_many_to_many_relations<relation_value_type>(
+      id,
+      objects,
+      attr,
+      [foreign_type, local_type](const char* relation_name) -> processing_many_to_many_key {
+        return {std::string{relation_name}, foreign_type, local_type};
+      },
+      [this, join_columns = std::move(join_columns)](const auto &obj) {
+        return object::make_object<relation_value_type>(join_columns.inverse_join_column, join_columns.join_column, obj, ptr_);
+      });
+  }
+
+private:
+  template<class PointerType>
+  void on_foreign_object(object::object_ptr<PointerType> &obj, const utils::foreign_attributes &attr) {
+    if (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Insert) || !obj || !obj.is_transient()) {
+      return;
+    }
+
+    insert_step_processor<PointerType> processor{ctx_};
+
+    auto result = processor.build(obj);
+    if (!result) {
+      throw query_builder_exception(result.release_error());
+    }
+  }
+
+  template<class LocalType, class ForeignType, class RelationKeyFactory, class RelationFactory>
+  void insert_many_to_many_relations(const char *id,
+                                     object::collection<object::object_ptr<ForeignType>> &objects,
+                                     const utils::foreign_attributes &attr,
+                                     RelationKeyFactory make_relation_key,
+                                     RelationFactory make_relation) {
+    if (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Insert)) {
+      return;
+    }
+
+    const auto key = make_relation_key(id);
+    if (ctx_.processing_many_to_many_relations_.find(key) != ctx_.processing_many_to_many_relations_.end()) {
+      return;
+    }
+
+    const auto it = ctx_.schema_.find(std::string{id});
+    if (it == ctx_.schema_.end()) {
+      throw query_builder_exception(error_code::UnknownType, "Unknown type for relation " + std::string{id});
+    }
+
+    if (std::type_index(typeid(LocalType)) != it->second.node().info().type_index()) {
+      throw query_builder_exception(error_code::InvalidRelationType, "Invalid relation type for " + std::string{id});
+    }
+
+    const auto cit = ctx_.contexts_by_type_.find(it->second.node().info().type_index());
+    if (cit == ctx_.contexts_by_type_.end()) {
+      throw query_builder_exception(error_code::UnknownType, "No query contexts for type " + it->second.node().name());
+    }
+
+    std::ignore = ctx_.processing_many_to_many_relations_.insert(key);
+    std::vector<std::unique_ptr<execute_step>> insert_relation_steps;
+    insert_step_processor<ForeignType> processor(ctx_);
+    for (auto &obj : objects) {
+      if (!obj) {
         continue;
       }
 
-      // Build INSERT into relation table with the 2 FK columns
+      if (obj.is_transient()) {
-      insert_step rel_step{};
+        auto result = processor.build(obj, true);
-      rel_step.query = executable_query{
+        if (!result) {
-        query::query::insert()
+          throw query_builder_exception(result.release_error());
-          .into(rel_table, {table_column{&rel_table, join_column}, table_column{&rel_table, inverse_join_column}})
+        };
-          .values({utils::database_type{current_entity_pk_}, utils::database_type{fk.value}})
+      }
-      };
+
-      relation_steps_.push_back(std::move(rel_step));
+      auto rel = make_relation(obj);
+
+      // access::process(*this, *rel);
+
+      insert_relation_steps.push_back(std::make_unique<insert_step_relation<LocalType>>(cit->second.insert, rel));
     }
+    ctx_.relation_steps_.insert(
+      ctx_.relation_steps_.end(),
+      std::make_move_iterator(insert_relation_steps.begin()),
+      std::make_move_iterator(insert_relation_steps.end()));
+    ctx_.processing_many_to_many_relations_.erase(key);
+  }
+
+  std::unique_ptr<execute_step> create_insert_step(const sql::query_context& query_ctx, const schema_node& node) {
+    if (node.pk_generator().type() == utils::generator_type::Manual) {
+      return std::make_unique<insert_step_pk_manual<ObjectType>>(query_ctx, ptr_);
+    }
+    if (node.pk_generator().type() == utils::generator_type::Identity) {
+      return std::make_unique<insert_step_pk_identity<ObjectType>>(query_ctx, ptr_, node.node().info().primary_key_attribute()->name());
+    }
+    return std::make_unique<insert_step_pk_generated<ObjectType>>(query_ctx, ptr_, node.pk_generator());
   }
-  template<class C>
-  static void on_has_many_to_many(const char * /*id*/, C &, const utils::foreign_attributes & ) {}
 
 private:
-  template<class EntityType>
+  query_builder_context& ctx_;
-  static std::pair<std::type_index, const void *> make_visit_key(const object::object_ptr<EntityType> &ptr) {
+  object::object_ptr<ObjectType> ptr_;
-    return {std::type_index(typeid(EntityType)), static_cast<const void *>(&(*ptr))};
+};
+
+template<class ObjectType>
+class insert_query_builder {
+public:
+  explicit insert_query_builder(const basic_schema &schema, const std::unordered_map<std::type_index, query_contexts> &contexts_by_type)
+  : schema_(schema)
+  , contexts_by_type_(contexts_by_type)
+  {}
+
+  utils::result<std::vector<std::unique_ptr<execute_step>>, utils::error> build(const object::object_ptr<ObjectType> &ptr) {
+    if (const auto it = schema_.find(typeid(ObjectType)); it == schema_.end()) {
+      return utils::failure(utils::error{error_code::UnknownType, "Unknown type for insert query"});
+    }
+
+    query_builder_context ctx{schema_, contexts_by_type_};
+    insert_step_processor<ObjectType> processor{ctx};
+
+    const auto result = processor.build(ptr);
+    if (!result) {
+      return utils::failure(result.err());
+    }
+
+    // relation inserts must run after all entity inserts were collected
+    for (auto &s : ctx.relation_steps_) {
+      ctx.steps_.push_back(std::move(s));
+    }
+    ctx.relation_steps_.clear();
+
+    return utils::ok(std::move(ctx.steps_));
   }
 
-  struct visit_key_hash {
-    size_t operator()(const std::pair<std::type_index, const void *> &p) const noexcept {
-      // combine hashes (simple + sufficient here)
-      const size_t h1 = p.first.hash_code();
-      const size_t h2 = std::hash<const void *>{}(p.second);
-      return h1 ^ (h2 + 0x9e3779b97f4a7c15ULL + (h1 << 6) + (h1 >> 2));
-    }
-  };
-
-  template<class EntityType>
-  void build_for(const object::object_ptr<EntityType> &ptr) {
-    if (!ptr) {
-      return;
-    }
-
-    const auto key = make_visit_key<EntityType>(ptr);
-    if (visited_.find(key) != visited_.end()) {
-      return;
-    }
-    visited_.insert(key);
-
-    const auto it = schema_.find(typeid(EntityType));
-    if (it == schema_.end()) {
-      throw query_builder_exception(query_build_error::UnknownType);
-    }
-
-    // 1) Traverse relations first => dependencies will be inserted before this object
-    access::process(*this, *ptr);
-
-    // 2) Build INSERT for this object
-    const auto &info = it->second.node().info();
-    insert_step step{};
-    if (info.has_primary_key()) {
-      step.pk_name = info.primary_key_attribute()->name();
-      step.pk_generator = it->second.generator_type();
-
-      step.pk_is_unset = [ptr, name = step.pk_name]() {
-        pk_unset_checker chk{name};
-        access::process(chk, *ptr);
-        return chk.unset;
-      };
-
-      step.set_pk = [ptr, name = step.pk_name](std::uint64_t v) {
-        pk_setter setter{name, v};
-        access::process(setter, *ptr);
-      };
-    }
-
-    if (info.has_primary_key() && step.pk_generator == utils::generator_type::Identity) {
-      const table_column pk_col(&it->second.table(), step.pk_name);
-      step.query = fetchable_query{query::query::insert().into(it->second.table()).values(*ptr).returning(pk_col)};
-      step.apply_returning = [ptr, pk_name = step.pk_name](const sql::record &rec) {
-        if (auto v = rec.at<std::uint64_t>(pk_name); v.has_value()) {
-          pk_setter setter{pk_name, *v};
-          access::process(setter, *ptr);
-        }
-      };
-    } else {
-      step.query = executable_query{query::query::insert().into(it->second.table()).values(*ptr)};
-    }
-    steps_.push_back(std::move(step));
-  }
-
-  template<class Pointer>
-  void on_foreign_object(Pointer &obj, const utils::foreign_attributes & /*attr*/) {
-    if (!obj) {
-      return;
-    }
-
-    // Dependency only matters if the referenced object must be inserted
-    if (obj.is_persistent()) {
-      return;
-    }
-
-    using dep_t = std::remove_reference_t<decltype(*obj)>;
-    build_for<dep_t>(obj);
-  }
 private:
   const basic_schema &schema_;
-
+  const std::unordered_map<std::type_index, query_contexts> &contexts_by_type_;
-  std::vector<insert_step> steps_;
-  std::vector<insert_step> relation_steps_;
-  std::unordered_set<std::pair<std::type_index, const void *>, visit_key_hash> visited_;
-
-  std::uint64_t current_entity_pk_{0};
 };
 }
 #endif //MATADOR_INSERT_QUERY_BUILDER_HPP

include/matador/query/insert_step.hpp

@@ -0,0 +1,180 @@
+#ifndef MATADOR_INSERT_STEP_HPP
+#define MATADOR_INSERT_STEP_HPP
+
+#include "matador/query/abstract_pk_generator.hpp"
+#include "matador/query/execute_step.hpp"
+#include "matador/query/error_code.hpp"
+
+#include "matador/object/object_cache.hpp"
+#include "matador/object/object_ptr.hpp"
+
+#include "matador/sql/execute_result.hpp"
+#include "matador/sql/resolver_service.hpp"
+#include "matador/sql/statement.hpp"
+
+namespace matador::query {
+template<typename ObjectType>
+utils::result<void, utils::error> finalize_inserted_object(object::object_ptr<ObjectType> &ptr,
+                                                           const utils::identifier& pk,
+                                                           object::object_cache &cache,
+                                                           const std::shared_ptr<sql::resolver_service> &resolver_service) {
+  if (!ptr) {
+    return utils::failure(utils::error(error_code::InvalidObject, "Inserted object is null."));
+  }
+
+  if (!resolver_service) {
+    return utils::failure(utils::error(error_code::UnknownType, "Missing resolver service."));
+  }
+
+  auto resolver = resolver_service->template object_resolver<ObjectType>();
+  if (!resolver) {
+    return utils::failure(utils::error(error_code::UnknownType, "Missing object resolver for inserted type."));
+  }
+
+  if (!cache.import<ObjectType>(pk, ptr.proxy(), resolver)) {
+    return utils::failure(utils::error(error_code::FailedToFindObject, "Object cache already contains another live proxy for inserted object."));
+  }
+
+  ptr.change_state(object::object_state::Persistent);
+  return utils::ok<void>();
+}
+
+template <typename ObjectType>
+class insert_step_pk_generated : public execute_step {
+public:
+  insert_step_pk_generated(sql::query_context ctx, const object::object_ptr<ObjectType>& ptr, abstract_pk_generator& pk_generator)
+  : execute_step(std::move(ctx))
+  , ptr_(ptr)
+  , pk_generator_(pk_generator){}
+
+  utils::result<void, utils::error> prepare(sql::executor& conn) override {
+    auto result = pk_generator_.next_id(conn);
+    if (!result.is_ok()) {
+      return utils::failure(result.err());
+    }
+    id_ = *result;
+    pk_accessor_.set(*ptr_, id_);
+
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> execute(sql::statement& stmt) override {
+    stmt.bind(*ptr_);
+
+    if (const auto exec_result = stmt.execute(); !exec_result.is_ok()) {
+      return utils::failure(exec_result.err());
+    }
+
+    ptr_.change_state(object::object_state::Persistent);
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> finalize(object::object_cache& cache, const resolver_service_ptr& resolver_service) override {
+    return finalize_inserted_object(ptr_, id_, cache, resolver_service);
+  }
+
+private:
+  object::object_ptr<ObjectType> ptr_;
+  abstract_pk_generator& pk_generator_;
+};
+
+template <typename ObjectType>
+class insert_step_pk_identity : public execute_step {
+public:
+  insert_step_pk_identity(sql::query_context ctx, const object::object_ptr<ObjectType>& ptr, std::string pk_column_name)
+  : execute_step(std::move(ctx))
+  , ptr_(ptr)
+  , pk_column_name_(std::move(pk_column_name)){}
+
+  utils::result<void, utils::error> prepare(sql::executor&) override {
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> execute(sql::statement& stmt) override {
+    stmt.bind(*ptr_);
+
+    auto result = stmt.fetch_one();
+    if (!result.is_ok()) {
+      return utils::failure(result.err());
+    }
+    if (!result.value().has_value()) {
+      return utils::failure(utils::error(error_code::FailedToFindObject, "Failed to insert object and retrieve identity."));
+    }
+
+    auto rec = result->value();
+    const auto& f = rec.at(pk_column_name_);
+    if (auto res = id_.assign(f.value()); !res.is_ok()) {
+      return utils::failure(res.err());
+    }
+    pk_accessor_.set(*ptr_, id_);
+
+    ptr_.change_state(object::object_state::Persistent);
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> finalize(object::object_cache& cache, const resolver_service_ptr& resolver_service) override {
+    return finalize_inserted_object(ptr_, id_, cache, resolver_service);
+  }
+
+private:
+  object::object_ptr<ObjectType> ptr_;
+  std::string pk_column_name_;
+};
+
+template <typename ObjectType>
+class insert_step_pk_manual : public execute_step {
+public:
+  insert_step_pk_manual(sql::query_context ctx, const object::object_ptr<ObjectType>& ptr)
+  : execute_step(std::move(ctx))
+  , ptr_(ptr) {}
+
+  utils::result<void, utils::error> prepare(sql::executor &) override {
+    return utils::ok<void>();
+  }
+  utils::result<void, utils::error> execute(sql::statement &stmt) override {
+    stmt.bind(*ptr_);
+    if (const auto exec_result = stmt.execute(); !exec_result.is_ok()) {
+      return utils::failure(exec_result.err());
+    }
+
+    id_ = object::primary_key_resolver::resolve_object(*ptr_).pk;
+    ptr_.change_state(object::object_state::Persistent);
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> finalize(object::object_cache& cache, const resolver_service_ptr& resolver_service) override {
+    return finalize_inserted_object(ptr_, id_, cache, resolver_service);
+  }
+
+private:
+  object::object_ptr<ObjectType> ptr_;
+};
+
+template <typename ObjectType>
+class insert_step_relation : public execute_step {
+public:
+  insert_step_relation(sql::query_context ctx, const object::object_ptr<ObjectType>& ptr)
+  : execute_step(std::move(ctx))
+  , ptr_(ptr) {}
+
+  utils::result<void, utils::error> prepare(sql::executor &) override {
+    return utils::ok<void>();
+  }
+  utils::result<void, utils::error> execute(sql::statement &stmt) override {
+    stmt.bind(*ptr_);
+    if (const auto exec_result = stmt.execute(); !exec_result.is_ok()) {
+      return utils::failure(exec_result.err());
+    }
+
+    return utils::ok<void>();
+  }
+
+  utils::result<void, utils::error> finalize(object::object_cache& /*cache*/, const resolver_service_ptr& /*resolver_service*/) override {
+    return utils::ok<void>();
+  }
+
+private:
+  object::object_ptr<ObjectType> ptr_;
+};
+}
+#endif //MATADOR_INSERT_STEP_HPP

include/matador/query/intermediates/executable_query.hpp

@@ -7,6 +7,7 @@
 #include "../../utils/result.hpp"
 
 namespace matador::sql {
+class dialect;
 class executor;
 class statement;
 struct execute_result;
@@ -21,8 +22,8 @@ public:
 
   [[nodiscard]] utils::result<sql::execute_result, utils::error> execute(const sql::executor &exec) const;
   [[nodiscard]] utils::result<sql::statement, utils::error> prepare(sql::executor &exec) const;
-  [[nodiscard]] sql::query_context compile(const sql::executor &exec) const;
+  [[nodiscard]] sql::query_context compile(const sql::dialect &d) const;
-  [[nodiscard]] std::string str(const sql::executor &exec) const;
+  [[nodiscard]] std::string str(const sql::dialect &d) const;
 };
 
 }

include/matador/query/intermediates/fetchable_query.hpp

@@ -75,7 +75,6 @@ public:
 
   [[nodiscard]] utils::result<sql::statement, utils::error> prepare(sql::executor &exec) const;
 
-  [[nodiscard]] std::string str(const sql::executor &exec) const;
   [[nodiscard]] std::string str(const sql::dialect &d) const;
   [[nodiscard]] sql::query_context compile(const sql::dialect &d) const;
 

include/matador/query/intermediates/query_alter_intermediate.hpp

@@ -11,6 +11,5 @@ public:
 
   [[nodiscard]] query_alter_table_intermediate table(const table &tab) const;
 };
-
 }
 #endif //MATADOR_QUERY_ALTER_INTERMEDIATE_HPP

include/matador/query/intermediates/query_create_intermediate.hpp

@@ -30,7 +30,7 @@ public:
   using query_intermediate::query_intermediate;
 
   query_create_table_columns_intermediate columns(std::initializer_list<object::attribute> attributes);
-  query_create_table_columns_intermediate columns(const std::list<object::attribute> &attributes);
+  query_create_table_columns_intermediate columns(const std::vector<object::attribute> &attributes);
   query_create_table_columns_intermediate columns(std::initializer_list<table_column> columns);
   query_create_table_columns_intermediate columns(const std::list<table_column> &columns);
   query_create_table_columns_intermediate columns(const std::vector<table_column> &columns);

include/matador/query/intermediates/query_execute_where_intermediate.hpp

@@ -2,6 +2,7 @@
 #define QUERY_EXECUTE_WHERE_INTERMEDIATE_HPP
 
 #include "matador/query/intermediates/executable_query.hpp"
+#include "matador/query/intermediates/fetchable_query.hpp"
 
 namespace matador::query {
 
@@ -14,9 +15,18 @@ class query_execute_where_intermediate : public executable_query
 public:
   using executable_query::executable_query;
 
+  template<typename... TableColumns>
+  fetchable_query returning(TableColumns... table_columns) {
+    const std::vector<table_column> tcv { std::forward<TableColumns>(table_columns)... };
+    return returning(tcv);
+  }
+
   query_execute_limit_intermediate limit(size_t limit);
   query_execute_order_by_intermediate order_by(const table_column &col);
   query_execute_order_by_intermediate order_by(std::initializer_list<table_column> columns);
+
+private:
+  fetchable_query returning(const std::vector<table_column>& tables);
 };
 
 }

include/matador/query/intermediates/query_intermediate.hpp

@@ -1,8 +1,6 @@
 #ifndef QUERY_INTERMEDIATE_HPP
 #define QUERY_INTERMEDIATE_HPP
 
-// #include "matador/query/query_data.hpp"
-
 #include <memory>
 
 namespace matador::query {
@@ -11,7 +9,7 @@ struct query_data;
 class query_intermediate {
 public:
   query_intermediate();
- query_intermediate(const std::shared_ptr<query_data> &context); // NOLINT(*-explicit-constructor)
+  query_intermediate(const std::shared_ptr<query_data> &context); // NOLINT(*-explicit-constructor)
 
 protected:
   std::shared_ptr<query_data> context_;

include/matador/query/intermediates/query_into_intermediate.hpp

@@ -2,22 +2,15 @@
 #define QUERY_INTO_INTERMEDIATE_HPP
 
 #include "matador/query/intermediates/executable_query.hpp"
-#include "matador/query/intermediates/fetchable_query.hpp"
+#include "matador/query/intermediates/query_values_intermediate.hpp"
 
 #include "matador/query/value_extractor.hpp"
 
+#include "matador/object/object_ptr.hpp"
+
 #include "matador/utils/placeholder.hpp"
 
 namespace matador::query {
-class table_column;
-
-class query_values_intermediate : public executable_query {
-public:
-  using executable_query::executable_query;
-
-  fetchable_query returning(const table_column &col);
-};
-
 class query_into_intermediate : public query_intermediate {
 public:
   using query_intermediate::query_intermediate;
@@ -30,6 +23,10 @@ public:
   query_values_intermediate values(const Type &obj) {
     return values(value_extractor::extract(obj));
   }
+  template<class Type>
+  query_values_intermediate values(const object::object_ptr<Type> &obj) {
+    return values(*obj);
+  }
 };
 
 }

include/matador/query/intermediates/query_select_intermediate.hpp

@@ -18,6 +18,7 @@ public:
   explicit query_select_intermediate(const std::vector<table_column>& columns);
 
   fetchable_query nextval(const std::string& sequence_name);
+  fetchable_query currval(const std::string& sequence_name);
 
   template<typename... Tables>
   query_from_intermediate from(const Tables&... tables) {

include/matador/query/intermediates/query_set_intermediate.hpp

@@ -9,14 +9,11 @@
 
 namespace matador::query {
 
-class query_set_intermediate : public executable_query
+class query_set_intermediate : public executable_query {
-{
 public:
   using executable_query::executable_query;
 
-  query_execute_where_intermediate where(std::unique_ptr<abstract_criteria> cond) {
+  query_execute_where_intermediate where(std::unique_ptr<abstract_criteria> cond);
-    return where_clause(std::move(cond));
-  }
 
 private:
   query_execute_where_intermediate where_clause(std::unique_ptr<abstract_criteria> &&cond);

include/matador/query/intermediates/query_update_intermediate.hpp

@@ -2,25 +2,38 @@
 #define QUERY_UPDATE_INTERMEDIATE_HPP
 
 #include "matador/query/intermediates/query_intermediate.hpp"
-
 #include "matador/query/intermediates/query_set_intermediate.hpp"
 
-#include "matador/query/key_value_generator.hpp"
+#include "matador/query/expression/column_expression.hpp"
+#include "matador/query/generator.hpp"
 
 #include "matador/query/internal/column_value_pair.hpp"
 
 namespace matador::query {
-
+namespace internal {
-class query_update_intermediate : public query_intermediate {
+class query_set_part;
+}
+class query_update_intermediate : public executable_query {
 public:
   explicit query_update_intermediate(const table& tab);
 
-  query_set_intermediate set(std::initializer_list<internal::column_value_pair> columns);
+  query_update_intermediate& set(const table_column& col, column_expression&& expression);
-  query_set_intermediate set(std::vector<internal::column_value_pair> &&columns);
   template<class Type>
   query_set_intermediate set(const Type &obj) {
-    return set(key_value_generator::generate(obj));
+    return set(generator::column_value_pairs(obj));
   }
+  template<class Type>
+  query_set_intermediate set() {
+    return set(generator::column_value_pairs<Type>());
+  }
+  query_execute_where_intermediate where(std::unique_ptr<abstract_criteria> cond);
+
+private:
+  query_execute_where_intermediate where_clause(std::unique_ptr<abstract_criteria> &&cond);
+  query_set_intermediate set(std::vector<internal::column_value_pair> &&key_value_pairs);
+
+private:
+  internal::query_set_part* query_set_part_{nullptr};
 };
 
 }

include/matador/query/intermediates/query_values_intermediate.hpp

@@ -0,0 +1,24 @@
+#ifndef MATADOR_QUERY_VALUES_INTERMEDIATE_H
+#define MATADOR_QUERY_VALUES_INTERMEDIATE_H
+
+#include "matador/query/intermediates/executable_query.hpp"
+#include "matador/query/intermediates/fetchable_query.hpp"
+
+namespace matador::query {
+class table_column;
+class query_values_intermediate : public executable_query {
+public:
+  using executable_query::executable_query;
+
+  template<typename... TableColumns>
+  fetchable_query returning(const TableColumns&... table_columns) {
+    const std::vector<table_column> tcv { table_columns... };
+    return returning(tcv);
+  }
+
+private:
+  fetchable_query returning(const std::vector<table_column>& tables);
+};
+}
+
+#endif //MATADOR_QUERY_VALUES_INTERMEDIATE_H

include/matador/query/internal/column_value_pair.hpp

@@ -2,6 +2,7 @@
 #define QUERY_KEY_VALUE_PAIR_HPP
 
 #include "matador/query/table_column.hpp"
+#include "../expression/column_expression.hpp"
 
 #include "matador/utils/placeholder.hpp"
 #include "matador/utils/types.hpp"
@@ -10,20 +11,21 @@ namespace matador::query::internal {
 
 class column_value_pair {
 public:
-  column_value_pair(table_column col, utils::database_type value);
+  column_value_pair() = default;
-  column_value_pair(std::string name, utils::database_type value);
+  column_value_pair(column_value_pair&& x) = default;
-  column_value_pair(const char *name, utils::database_type value);
+  column_value_pair& operator=(column_value_pair&& x) = default;
-  column_value_pair(const char *name, utils::placeholder p);
+  column_value_pair(table_column col, column_expression_ptr expression);
 
   friend bool operator==(const column_value_pair &lhs, const column_value_pair &rhs);
   friend bool operator!=(const column_value_pair &lhs, const column_value_pair &rhs);
 
   [[nodiscard]] const table_column& col() const;
-  [[nodiscard]] const std::variant<utils::placeholder, utils::database_type>& value() const;
+  [[nodiscard]] const abstract_column_expression& expression() const;
 
 private:
   table_column column_;
-  std::variant<utils::placeholder, utils::database_type> value_;
+  column_expression_ptr expression_;
+
 };
 
 }

include/matador/query/internal/query_parts.hpp

@@ -15,8 +15,6 @@
 #include <list>
 #include <memory>
 
-#include "matador/object/restriction.hpp"
-
 namespace matador::query::internal {
 
 class query_alter_part final : public query_part {
@@ -139,6 +137,19 @@ private:
   std::string sequence_name_;
 };
 
+class query_select_currval_part final : public query_part {
+public:
+  explicit query_select_currval_part(std::string sequence_name);
+
+  [[nodiscard]] const std::string& sequence_name() const;
+
+private:
+  void accept(query_part_visitor &visitor) override;
+
+private:
+  std::string sequence_name_;
+};
+
 
 /**
  * Represents the SQL FROM part
@@ -374,15 +385,15 @@ private:
 class query_set_part final : public query_part
 {
 public:
-  explicit query_set_part(const std::vector<internal::column_value_pair>& key_value_pairs);
+  explicit query_set_part(std::vector<column_value_pair>&& key_value_pairs);
 
-  [[nodiscard]] const std::vector<internal::column_value_pair>& column_values() const;
+  [[nodiscard]] const std::vector<column_value_pair>& column_values() const;
 
 private:
   void accept(query_part_visitor &visitor) override;
 
 private:
-  std::vector<internal::column_value_pair> key_value_pairs_;
+  std::vector<column_value_pair> key_value_pairs_;
 };
 
 class query_delete_part final : public query_part

include/matador/query/key_value_generator.hpp

@@ -26,14 +26,16 @@ public:
     return result;
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template < class V >
-  void on_primary_key(const char *id, V &x, const utils::primary_key_attribute& /*attr*/ = utils::default_pk_attributes) {
+  void on_primary_key(const char *id, V &x, const utils::primary_key_attribute& /*attr*/) {
     result_.emplace_back(id, x);
   }
-  void on_revision(const char *id, uint64_t &/*rev*/);
+  void on_revision(const char *id, uint64_t &/*rev*/) const;
 
   template<typename Type>
-  void on_attribute(const char *id, Type &x, const utils::field_attributes &/*attr*/ = utils::null_attributes) {
+  void on_attribute(const char *id, Type &x, const utils::field_attributes &/*attr*/) {
     result_.emplace_back(id, x);
   }
 
@@ -42,7 +44,7 @@ public:
     result_.emplace_back(id, fk_value_extractor_.extract(*x));
   }
   template<class Type, template < class ... > class Pointer>
-  void on_has_one(const char *id, Pointer<Type> &x, const utils::foreign_attributes &/*attr*/) {
+  void on_has_one(const char *id, Pointer<Type> &x, const char * /*join_column*/, const utils::foreign_attributes &/*attr*/) {
     result_.emplace_back(id, fk_value_extractor_.extract(*x));
   }
   template<class ContainerType>

include/matador/query/manual_pk_generator.hpp

@@ -0,0 +1,14 @@
+#ifndef MATADOR_MANUAL_PK_GENERATOR_HPP
+#define MATADOR_MANUAL_PK_GENERATOR_HPP
+
+#include "matador/query/abstract_pk_generator.hpp"
+
+namespace matador::query {
+class manual_pk_generator : public abstract_pk_generator {
+public:
+    manual_pk_generator();
+    [[nodiscard]] utils::result<int64_t, utils::error> next_id(const sql::executor& exec) override;
+    [[nodiscard]] utils::result<int64_t, utils::error> current_id(const sql::executor& exec) override;
+};
+}
+#endif //MATADOR_MANUAL_PK_GENERATOR_HPP

include/matador/query/meta_table_macro.hpp

@@ -18,7 +18,7 @@ TABLE_NAME##_table()\
 : TABLE_NAME##_table(#TABLE_NAME) \
 {} \
 TABLE_NAME##_table(const std::string& alias) \
-: typed_table(#TABLE_NAME, alias, {MAP(FIELD_STRING, __VA_ARGS__)}) \
+: typed_table(#TABLE_NAME, alias, {MAP(FIELD_STRING, __VA_ARGS__)}, {}, {}) \
 MAP(INIT_FIELD, __VA_ARGS__) \
 {} \
 MAP(FIELD, __VA_ARGS__) \

include/matador/query/query.hpp

@@ -17,25 +17,20 @@ table_column avg(const std::string &column);
 table_column maximum(const std::string &column);
 table_column minimum(const std::string &column);
 
-class query
+[[nodiscard]] query_create_intermediate create();
-{
+[[nodiscard]] query_drop_intermediate drop();
-public:
+[[nodiscard]] query_select_intermediate select();
-  [[nodiscard]] static query_create_intermediate create();
+[[nodiscard]] query_select_intermediate select(std::initializer_list<table_column> columns);
-  [[nodiscard]] static query_drop_intermediate drop();
+[[nodiscard]] query_select_intermediate select(const std::vector<table_column>& columns);
-  [[nodiscard]] static query_select_intermediate select();
+[[nodiscard]] query_select_intermediate select(const std::vector<std::string> &column_names);
-  [[nodiscard]] static query_select_intermediate select(std::initializer_list<table_column> columns);
+template<class Type>
-  [[nodiscard]] static query_select_intermediate select(const std::vector<table_column>& columns);
+[[nodiscard]] query_select_intermediate select(const schema &scm) {
-  [[nodiscard]] static query_select_intermediate select(const std::vector<std::string> &column_names);
+  return select(generator::columns<Type>(scm));
-  template<class Type>
+}
-  [[nodiscard]] static query_select_intermediate select(const schema &scm) {
+[[nodiscard]] query_insert_intermediate insert();
-    return select(generator::columns<Type>(scm));
+[[nodiscard]] query_update_intermediate update(const table &table);
-  }
+[[nodiscard]] query_delete_intermediate remove();
-  [[nodiscard]] static query_insert_intermediate insert();
-  [[nodiscard]] static query_update_intermediate update(const table &table);
-  [[nodiscard]] static query_delete_intermediate remove();
-
-  [[nodiscard]] static query_alter_intermediate alter();
-};
 
+[[nodiscard]] query_alter_intermediate alter();
 }
 #endif //QUERY_QUERY_HPP

include/matador/query/query_builder.hpp

@@ -5,6 +5,7 @@
 #include "matador/query/query_data.hpp"
 
 #include "matador/sql/query_context.hpp"
+#include "matador/sql/interface/connection_impl.hpp"
 
 #include "matador/utils/placeholder.hpp"
 
@@ -12,7 +13,6 @@
 #include <optional>
 
 namespace matador::sql {
-class connection_impl;
 class dialect;
 }
 
@@ -29,11 +29,10 @@ struct value_visitor;
 
 class query_builder final : public query_part_visitor {
 public:
-  sql::query_context compile(const query_data &data,
+  sql::query_context build(const query_data &data,
-                             const sql::dialect &d,
+                           const sql::dialect &d,
-                             std::optional<std::reference_wrapper<const sql::connection_impl>> conn);
+                           std::optional<std::reference_wrapper<const sql::connection_impl>> conn);
 
-protected:
   void visit(internal::query_alter_part& part) override;
   void visit(internal::query_alter_table_part& part) override;
   void visit(internal::query_add_key_constraint_part& part) override;
@@ -46,6 +45,7 @@ protected:
 
   void visit(internal::query_select_part &part) override;
   void visit(internal::query_select_nextval_part &part) override;
+  void visit(internal::query_select_currval_part &part) override;
   void visit(internal::query_from_part &part) override;
   void visit(internal::query_join_table_part &part) override;
   void visit(internal::query_join_query_part &part) override;
@@ -83,8 +83,10 @@ protected:
 
   static std::string build_table_name(sql::dialect_token token, const sql::dialect &d, const table& t);
   static std::string build_table_name(const sql::dialect &d, const table& t);
+  static std::string determine_value(const sql::dialect &d, sql::query_context& ctx, const abstract_column_expression &exp);
   static std::string determine_value(value_visitor &visitor, const std::variant<utils::placeholder, utils::database_type> &val);
 
+
   [[nodiscard]] std::string build_add_constraint_string(const table_constraint& c) const;
   [[nodiscard]] std::string build_drop_constraint_string(const table_constraint& c) const;
   static std::string build_constraint_name(const table_constraint& c);

include/matador/query/query_builder_exception.hpp

@@ -3,28 +3,20 @@
 
 #include "matador/utils/error.hpp"
 
+#include "matador/query/error_code.hpp"
+
 #include <cstdint>
 
 namespace matador::query {
 
-enum class query_build_error : std::uint8_t {
-  Ok = 0,
-  UnknownType,
-  MissingPrimaryKey,
-  MissingObject,
-  UnexpectedError,
-  QueryError
-};
-
 class query_builder_exception final : public std::exception {
 public:
-  explicit query_builder_exception(query_build_error error, utils::error &&err = {});
+  explicit query_builder_exception(utils::error &&err);
+  query_builder_exception(error_code error, std::string &&msg);
 
-  [[nodiscard]] query_build_error error_type() const;
   [[nodiscard]] const utils::error &error() const;
 
 private:
-  const query_build_error error_type_;
   utils::error error_;
 };
 

include/matador/query/query_builder_utils.hpp

@@ -0,0 +1,60 @@
+#ifndef MATADOR_QUERY_BUILDER_UTILS_HPP
+#define MATADOR_QUERY_BUILDER_UTILS_HPP
+
+#include <functional>
+#include <map>
+#include <typeindex>
+
+namespace matador::query {
+template<class EntityType>
+static std::pair<std::type_index, const void *> make_entity_visit_key(const EntityType &ptr) {
+  return {std::type_index(typeid(EntityType)), static_cast<const void *>(&ptr)};
+}
+
+struct entity_visit_key_hash {
+  size_t operator()(const std::pair<std::type_index, const void *> &p) const noexcept {
+    const size_t h1 = p.first.hash_code();
+    const size_t h2 = std::hash<const void *>{}(p.second);
+    return h1 ^ (h2 + 0x9e3779b97f4a7c15ULL + (h1 << 6) + (h1 >> 2));
+  }
+};
+
+struct processing_many_to_many_key {
+  std::string id;
+  std::type_index local_type{typeid(void)};
+  std::type_index foreign_type{typeid(void)};
+  bool operator==(processing_many_to_many_key const &other) const {
+    return local_type == other.local_type && foreign_type == other.foreign_type && id == other.id;
+  }
+};
+
+template<class LocalType, typename ForeignType>
+static processing_many_to_many_key make_processing_many_to_many_key(const std::string &id) {
+  return {id, std::type_index(typeid(LocalType)), std::type_index(typeid(ForeignType))};
+}
+
+struct processing_many_to_many_key_hash {
+  size_t operator()(const processing_many_to_many_key &p) const noexcept {
+    size_t seed = std::hash<std::type_index>{}(p.local_type);
+
+    const size_t foreign_hash = std::hash<std::type_index>{}(p.foreign_type);
+    seed ^= foreign_hash + 0x9e3779b97f4a7c15ULL + (seed << 6) + (seed >> 2);
+
+    const size_t id_hash = std::hash<std::string>{}(p.id);
+    seed ^= id_hash + 0x9e3779b97f4a7c15ULL + (seed << 6) + (seed >> 2);
+
+    return seed;
+  }
+};
+
+struct query_builder_context {
+  const basic_schema &schema_;
+  const std::unordered_map<std::type_index, query_contexts> &contexts_by_type_;
+
+  std::vector<std::unique_ptr<execute_step>> steps_{};
+  std::vector<std::unique_ptr<execute_step>> relation_steps_{};
+  std::unordered_set<std::pair<std::type_index, const void *>, entity_visit_key_hash> visited_{};
+  std::unordered_set<processing_many_to_many_key, processing_many_to_many_key_hash> processing_many_to_many_relations_{};
+};
+}
+#endif //MATADOR_QUERY_BUILDER_UTILS_HPP