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

This reverts commit 8914c06833.

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/test/CMakeLists.txt

@@ -25,6 +25,8 @@ set(TEST_SOURCES
   ../../../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

include/matador/object/attribute.hpp

@@ -34,6 +34,7 @@ public:
   [[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;
@@ -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

@@ -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"
 
@@ -12,13 +12,99 @@
 
 namespace matador::object {
 
+// has many primitive
+// relation<OwnerType, PrimitiveType>
+// has many ptr
+// relation<OwnerType, ObjectType>
+// has many to many
+// relation<OwnerType, ForeignType>
 
-template<typename Type>
+template < class RelationType >
-class collection_proxy final {
+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 iterator = typename std::vector<value_type>::iterator;
+  using reference = Type&;
-  using const_iterator = typename std::vector<value_type>::const_iterator;
+  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 : 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;
 
@@ -34,17 +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_) {
@@ -70,5 +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/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:

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>
@@ -35,6 +36,23 @@ struct cache_entry : cache_entry_base {
   }
 };
 
+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.
@@ -83,6 +102,7 @@ public:
       // found entry, return std::shared_ptr of proxy
       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;
       }
 
@@ -96,6 +116,8 @@ 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;
     }
@@ -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;
   }
 
@@ -325,6 +416,7 @@ private:
 
 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

@@ -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);
@@ -71,6 +75,9 @@ 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;
     }
 
@@ -98,6 +105,7 @@ public:
     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>
@@ -111,6 +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;
     }
@@ -120,9 +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;
@@ -135,7 +145,7 @@ private:
 
 template<typename ValueType>
 void object_generator::on_primary_key(const char *id, ValueType &x, const utils::primary_key_attribute& attr) {
-    utils::constraints cs = utils::constraints::PrimaryKey;
+    auto cs = utils::constraints::PrimaryKey;
     if (attr.generator() == utils::generator_type::Identity) {
         cs |= utils::constraints::Identity;
     }
@@ -160,7 +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

@@ -26,87 +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_; }
+  [[nodiscard]] bool has_primary_key() const {
-  void primary_key(const utils::identifier &pk) { pk_ = pk; }
+    std::lock_guard lock(mutex_);
+    return !pk_.is_null();
+  }
+
+  [[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 { return state_ == state; }
+
+  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);
+    std::lock_guard lock(mutex_);
+    state_ = state;
   }
 private:
-  Type* resolve() const {
+  std::shared_ptr<Type> resolve_object() const {
+    std::shared_ptr<Type> current;
+    std::shared_ptr<object_resolver<Type>> resolver;
+    utils::identifier pk;
+
+    {
+      std::lock_guard lock(mutex_);
       if (obj_) {
-      return obj_.get();
+        return obj_;
       }
 
-    std::lock_guard lock(mutex_);
+      resolver = resolver_.lock();
-    auto resolver = resolver_.lock();
       if (!resolver) {
         return nullptr;
-      // Todo: Add states (Detached, Attached, Transient) - if attached an no resolver is available throw runtime exception
-      // throw std::runtime_error("Detached proxy (session expired)");
       }
 
-    const_cast<std::shared_ptr<Type>&>(obj_) = resolver->resolve(pk_);
+      pk = pk_;
-
-    return obj_.get();
     }
 
+    current = resolver->resolve(pk);
+
+    {
+      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

@@ -19,62 +19,148 @@ class object_ptr {
 public:
 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=(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 {
-  void reset(const std::shared_ptr<object_proxy<Type>>& proxy) { proxy_ = proxy; }
+    return proxy_ ? proxy_->object() : nullptr;
+  }
 
-  operator bool() const { return valid(); }
+  void reset() {
-  [[nodiscard]] bool valid() const { return proxy_ != nullptr && !proxy_->empty(); }
+    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(); }
+
-  [[nodiscard]] bool is_state(const object_state state) const { return proxy_->is_state(state); }
+  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:
+  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_{};
 };

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

@@ -88,9 +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;
       };
 

include/matador/object/relation_completer.hpp

@@ -172,7 +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;
@@ -191,7 +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
@@ -222,8 +222,7 @@ 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>;
 
@@ -367,7 +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/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/builder.hpp

@@ -8,15 +8,16 @@
 #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)
-    : type_(type), size_(size) {}
+  : type_(type), size_(size) {
+  }
 
   [[nodiscard]] const utils::basic_type &type() const { return type_; }
   [[nodiscard]] size_t size() const { return size_; }
@@ -30,14 +31,16 @@ template<typename Type>
 class typed_data_type final : public data_type {
 public:
   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)
-    : 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>;
@@ -57,9 +60,12 @@ 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 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);
@@ -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/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/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_evaluator.hpp

@@ -19,7 +19,7 @@ public:
     void visit(const value_expression& node) override;
     void visit(const placeholder_expression& node) override;
 
-    const std::string& result() const;
+    [[nodiscard]] const std::string& result() const;
 
 private:
     const sql::dialect &dialect_;

include/matador/query/fk_value_extractor.hpp

@@ -12,14 +12,12 @@ 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_;
   }

include/matador/query/insert_query_builder.hpp

@@ -1,9 +1,8 @@
 #ifndef MATADOR_INSERT_QUERY_BUILDER_HPP
 #define MATADOR_INSERT_QUERY_BUILDER_HPP
 
-#include <utility>
-
 #include "matador/object/collection.hpp"
+#include "matador/object/object_ptr.hpp"
 
 #include "matador/query/basic_schema.hpp"
 #include "matador/query/intermediates/executable_query.hpp"
@@ -11,6 +10,7 @@
 #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"
 
@@ -56,36 +56,57 @@ private:
   std::string join_column_;
 };
 
-template<class ObjectType>
+template < typename ObjectType >
-class insert_query_builder {
+class insert_step_processor {
 public:
-  explicit insert_query_builder(const basic_schema &schema, const std::unordered_map<std::type_index, query_contexts> &contexts_by_type)
+  explicit insert_step_processor(query_builder_context &ctx)
-  : schema_(schema)
+  : ctx_{ctx}
-  , contexts_by_type_{contexts_by_type}
   {}
 
-  utils::result<std::vector<std::unique_ptr<insert_step>>, utils::error> build(const object::object_ptr<ObjectType> &ptr) {
+  utils::result<void, utils::error> build(object::object_ptr<ObjectType> ptr, const bool as_relation_step = false) {
-    if (const auto it = schema_.find(typeid(ObjectType)); it == schema_.end()) {
+    if (!ptr) {
-      return utils::failure(utils::error{error_code::UnknownType, "Unknown type for insert query"});
+      return utils::failure(utils::error{error_code::InvalidObject, "Object is null"});
     }
-
-    steps_.clear();
-    visited_.clear();
-
     ptr_ = ptr;
-    const auto result = build_for(ptr, steps_);
+
+    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();
-    if (!result) {
-      return utils::failure(result.err());
-    }
 
-    // relation inserts must run after all entity inserts were collected
+    return utils::ok<void>();
-    for (auto &s : relation_steps_) {
-      steps_.push_back(std::move(s));
-    }
-    relation_steps_.clear();
-
-    return utils::ok(std::move(steps_));
   }
 
   template < class PrimaryKeyType >
@@ -103,36 +124,51 @@ public:
   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::Insert)) {
       return;
     }
 
     has_many_linker<ObjectType> linker(ptr_, join_column);
+    insert_step_processor<CollectionType> processor{ctx_};
     for (auto &obj : objects) {
+      if (!obj) {
+        continue;
+      }
+
       if (obj.is_transient()) {
-        build_for(obj, relation_steps_);
+        auto result = processor.build(obj, true);
+        if (!result) {
+          throw query_builder_exception(result.release_error());
+        }
       }
 
       access::process(linker, *obj);
     }
-
   }
+
   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 = schema_.find(std::string{id});
+    const auto it = ctx_.schema_.find(std::string{id});
-    if (it == schema_.end()) {
+    if (it == ctx_.schema_.end()) {
       throw query_builder_exception(error_code::UnknownType, "Unknown type " + std::string{id});
     }
 
@@ -141,204 +177,190 @@ public:
       throw query_builder_exception(error_code::InvalidRelationType, "Invalid relation type");
     }
 
-    const auto cit = contexts_by_type_.find(it->second.node().info().type_index());
+    const auto cit = ctx_.contexts_by_type_.find(it->second.node().info().type_index());
-    if (cit == contexts_by_type_.end()) {
+    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);
 
-      relation_steps_.push_back(std::make_unique<insert_step_relation<relation_value_type>>(cit->second.insert, rel));
+      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) {
+    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;
     }
 
-    if (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Insert)) {
-      return;
-    }
-
-    if (processing_many_to_many_relations_.find(id) != processing_many_to_many_relations_.end()) {
-      return;
-    }
-
-    const auto it = schema_.find(std::string{id});
-    if (it == schema_.end()) {
-      throw query_builder_exception(error_code::UnknownType, "Unknown type");
-    }
-
     using relation_value_type = object::many_to_many_relation<ObjectType, ForeignType>;
-    if (std::type_index(typeid(relation_value_type)) != it->second.node().info().type_index()) {
+    const std::type_index foreign_type{typeid(ForeignType)};
-      throw query_builder_exception(error_code::InvalidRelationType, "Invalid relation type");
+    const std::type_index local_type{typeid(ObjectType)};
-    }
+    insert_many_to_many_relations<relation_value_type>(
-
+      id,
-    const auto cit = contexts_by_type_.find(it->second.node().info().type_index());
+      objects,
-    if (cit == contexts_by_type_.end()) {
+      attr,
-      throw query_builder_exception(error_code::UnknownType, "Unknown type");
+      [foreign_type, local_type](const char* relation_name) -> processing_many_to_many_key {
-    }
+        return {std::string{relation_name}, local_type, foreign_type};
-
+      },
-    std::ignore = processing_many_to_many_relations_.insert(id);
+      [this, join_column, inverse_join_column](const auto &obj) {
-    std::vector<std::unique_ptr<insert_step>> insert_relation_steps;
+        return object::make_object<relation_value_type>(join_column, inverse_join_column, ptr_, obj);
-    for (auto &obj : objects) {
+      });
-      if (!obj) {
-        continue;
-      }
-
-      // Ensure target exists as dependency (deps first)
-      if (obj.is_transient()) {
-        build_for(obj, relation_steps_);
-      }
-
-      auto rel = object::make_object<relation_value_type>(join_column, inverse_join_column, ptr_, obj);
-
-      access::process(*this, *rel);
-
-      insert_relation_steps.push_back(std::make_unique<insert_step_relation<relation_value_type>>(cit->second.insert, rel));
-    }
-    relation_steps_.insert(relation_steps_.end(), std::make_move_iterator(insert_relation_steps.begin()), std::make_move_iterator(insert_relation_steps.end()));
-    processing_many_to_many_relations_.erase(id);
   }
 
   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 (!utils::is_cascade_type_set(attr.cascade(), utils::cascade_type::Insert)) {
+    if (id == nullptr) {
-      return;
-    }
-
-    if (processing_many_to_many_relations_.find(id) != processing_many_to_many_relations_.end()) {
       return;
     }
 
     object::join_columns_collector collector;
     auto join_columns = collector.collect<ForeignType>();
-
+    if (join_columns.join_column.empty() || join_columns.inverse_join_column.empty()) {
-    const auto it = schema_.find(std::string{id});
+      return;
-    if (it == schema_.end()) {
-      throw query_builder_exception(error_code::UnknownType, "Unknown type");
     }
 
     using relation_value_type = object::many_to_many_relation<ForeignType, ObjectType>;
-
+    const std::type_index foreign_type{typeid(ForeignType)};
-    if (std::type_index(typeid(relation_value_type)) != it->second.node().info().type_index()) {
+    const std::type_index local_type{typeid(ObjectType)};
-      throw query_builder_exception(error_code::InvalidRelationType, "Invalid relation type");
+    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_);
+      });
   }
 
-    const auto cit = contexts_by_type_.find(it->second.node().info().type_index());
+private:
-    if (cit == contexts_by_type_.end()) {
+  template<class PointerType>
-      throw query_builder_exception(error_code::UnknownType, "Unknown type");
+  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;
     }
 
-    std::ignore = processing_many_to_many_relations_.insert(id);
+    insert_step_processor<PointerType> processor{ctx_};
-    std::vector<std::unique_ptr<insert_step>> insert_relation_steps;
+
+    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;
       }
 
-      // Ensure target exists as dependency (deps first)
       if (obj.is_transient()) {
-        build_for(obj, relation_steps_);
+        auto result = processor.build(obj, true);
+        if (!result) {
+          throw query_builder_exception(result.release_error());
+        };
       }
 
-      auto rel = object::make_object<relation_value_type>(join_columns.inverse_join_column, join_columns.join_column, obj, ptr_);
+      auto rel = make_relation(obj);
 
-      access::process(*this, *rel);
+      // access::process(*this, *rel);
 
-      insert_relation_steps.push_back(std::make_unique<insert_step_relation<relation_value_type>>(cit->second.insert, rel));
+      insert_relation_steps.push_back(std::make_unique<insert_step_relation<LocalType>>(cit->second.insert, rel));
     }
-    relation_steps_.insert(relation_steps_.end(), std::make_move_iterator(insert_relation_steps.begin()), std::make_move_iterator(insert_relation_steps.end()));
+    ctx_.relation_steps_.insert(
-    processing_many_to_many_relations_.erase(id);
+      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());
   }
 
 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))};
-  }
-
-  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>
+template<class ObjectType>
-  utils::result<void, utils::error> build_for(const object::object_ptr<EntityType> &ptr, std::vector<std::unique_ptr<insert_step>> &steps) {
+class insert_query_builder {
-    if (!ptr) {
+public:
-      return utils::failure(utils::error{error_code::InvalidObject, "Object is null"});
+  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"});
     }
 
-    const auto key = make_visit_key<EntityType>(ptr);
+    query_builder_context ctx{schema_, contexts_by_type_};
-    if (visited_.find(key) != visited_.end()) {
+    insert_step_processor<ObjectType> processor{ctx};
-      return utils::ok<void>();
-    }
-    visited_.insert(key);
 
-    const auto it = schema_.find(typeid(EntityType));
+    const auto result = processor.build(ptr);
-    if (it == schema_.end()) {
+    if (!result) {
-      return utils::failure(utils::error{error_code::UnknownType, "Unknown type"});
+      return utils::failure(result.err());
     }
 
-    // 1) Traverse relations first => dependencies will be inserted before this object
+    // relation inserts must run after all entity inserts were collected
-    try {
+    for (auto &s : ctx.relation_steps_) {
-      access::process(*this, *ptr);
+      ctx.steps_.push_back(std::move(s));
-    } catch (const query_builder_exception &ex) {
+    }
-      return utils::failure(ex.error());
+    ctx.relation_steps_.clear();
+
+    return utils::ok(std::move(ctx.steps_));
   }
 
-    // 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 = contexts_by_type_.find(it->second.node().info().type_index());
-    if (cit == contexts_by_type_.end()) {
-      return utils::failure(utils::error{error_code::UnknownType, "Unknown type"});
-    }
-
-    if (it->second.pk_generator().type() == utils::generator_type::Manual) {
-      steps.push_back(std::make_unique<insert_step_pk_manual<EntityType>>(cit->second.insert, ptr));
-    } else if (it->second.pk_generator().type() == utils::generator_type::Identity) {
-      steps.push_back(std::make_unique<insert_step_pk_identity<EntityType>>(cit->second.insert, ptr, info.primary_key_attribute()->name()));
-    } else {
-      steps.push_back(std::make_unique<insert_step_pk_generated<EntityType>>(cit->second.insert, ptr, it->second.pk_generator()));
-    }
-
-    return utils::ok<void>();
-  }
-
-  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, steps_);
-  }
 private:
   const basic_schema &schema_;
   const std::unordered_map<std::type_index, query_contexts> &contexts_by_type_;
-
-  object::object_ptr<ObjectType> ptr_;
-
-  std::vector<std::unique_ptr<insert_step>> steps_;
-  std::vector<std::unique_ptr<insert_step>> relation_steps_;
-  std::unordered_set<std::pair<std::type_index, const void *>, visit_key_hash> visited_;
-  std::unordered_set<std::string> processing_many_to_many_relations_;
 };
 }
 #endif //MATADOR_INSERT_QUERY_BUILDER_HPP

include/matador/query/insert_step.hpp

@@ -1,43 +1,49 @@
 #ifndef MATADOR_INSERT_STEP_HPP
 #define MATADOR_INSERT_STEP_HPP
 
-#include <utility>
+#include "matador/query/abstract_pk_generator.hpp"
-
+#include "matador/query/execute_step.hpp"
-#include "matador/utils/primary_key_accessor.hpp"
+#include "matador/query/error_code.hpp"
-#include "matador/utils/error.hpp"
-#include "matador/utils/result.hpp"
 
+#include "matador/object/object_cache.hpp"
 #include "matador/object/object_ptr.hpp"
 
-#include "matador/sql/query_context.hpp"
-#include "matador/sql/executor.hpp"
 #include "matador/sql/execute_result.hpp"
+#include "matador/sql/resolver_service.hpp"
 #include "matador/sql/statement.hpp"
 
-#include "matador/query/error_code.hpp"
-#include "matador/query/abstract_pk_generator.hpp"
-
 namespace matador::query {
-class insert_step {
+template<typename ObjectType>
-public:
+utils::result<void, utils::error> finalize_inserted_object(object::object_ptr<ObjectType> &ptr,
-  explicit insert_step(sql::query_context ctx)
+                                                           const utils::identifier& pk,
-  : ctx_(std::move(ctx)) {}
+                                                           object::object_cache &cache,
-  virtual ~insert_step() = default;
+                                                           const std::shared_ptr<sql::resolver_service> &resolver_service) {
+  if (!ptr) {
+    return utils::failure(utils::error(error_code::InvalidObject, "Inserted object is null."));
+  }
 
-  virtual utils::result<void, utils::error> prepare(sql::executor &conn) = 0;
+  if (!resolver_service) {
-  virtual utils::result<void, utils::error> insert(sql::statement &stmt) = 0;
+    return utils::failure(utils::error(error_code::UnknownType, "Missing resolver service."));
+  }
 
-  [[nodiscard]] const sql::query_context& ctx() const { return ctx_; }
+  auto resolver = resolver_service->template object_resolver<ObjectType>();
-protected:
+  if (!resolver) {
-  utils::primary_key_accessor pk_accessor_;
+    return utils::failure(utils::error(error_code::UnknownType, "Missing object resolver for inserted type."));
-  sql::query_context ctx_;
+  }
-};
+
+  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 insert_step {
+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)
-  : insert_step(std::move(ctx))
+  : execute_step(std::move(ctx))
   , ptr_(ptr)
   , pk_generator_(pk_generator){}
 
@@ -46,12 +52,13 @@ public:
     if (!result.is_ok()) {
       return utils::failure(result.err());
     }
-    pk_accessor_.set(*ptr_, utils::identifier{*result});
+    id_ = *result;
+    pk_accessor_.set(*ptr_, id_);
 
     return utils::ok<void>();
   }
 
-  utils::result<void, utils::error> insert(sql::statement& stmt) override {
+  utils::result<void, utils::error> execute(sql::statement& stmt) override {
     stmt.bind(*ptr_);
 
     if (const auto exec_result = stmt.execute(); !exec_result.is_ok()) {
@@ -62,16 +69,20 @@ public:
     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 insert_step {
+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)
-  : insert_step(std::move(ctx))
+  : execute_step(std::move(ctx))
   , ptr_(ptr)
   , pk_column_name_(std::move(pk_column_name)){}
 
@@ -79,7 +90,7 @@ public:
     return utils::ok<void>();
   }
 
-  utils::result<void, utils::error> insert(sql::statement& stmt) override {
+  utils::result<void, utils::error> execute(sql::statement& stmt) override {
     stmt.bind(*ptr_);
 
     auto result = stmt.fetch_one();
@@ -92,56 +103,64 @@ public:
 
     auto rec = result->value();
     const auto& f = rec.at(pk_column_name_);
-    utils::identifier id;
+    if (auto res = id_.assign(f.value()); !res.is_ok()) {
-    if (auto res = id.assign(f.value()); !res.is_ok()) {
       return utils::failure(res.err());
     }
-    pk_accessor_.set(*ptr_, id);
+    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 insert_step {
+class insert_step_pk_manual : public execute_step {
 public:
   insert_step_pk_manual(sql::query_context ctx, const object::object_ptr<ObjectType>& ptr)
-  : insert_step(std::move(ctx))
+  : 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> insert(sql::statement &stmt) override {
+  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 insert_step {
+class insert_step_relation : public execute_step {
 public:
   insert_step_relation(sql::query_context ctx, const object::object_ptr<ObjectType>& ptr)
-  : insert_step(std::move(ctx))
+  : 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> insert(sql::statement &stmt) override {
+  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());
@@ -150,6 +169,10 @@ public:
     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_;
 };

include/matador/query/intermediates/executable_query.hpp

@@ -23,7 +23,7 @@ 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::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_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 {

include/matador/query/internal/column_value_pair.hpp

@@ -12,10 +12,6 @@ namespace matador::query::internal {
 class column_value_pair {
 public:
   column_value_pair() = default;
-  // column_value_pair(table_column col, utils::database_type value);
-  // column_value_pair(const std::string& name, utils::database_type value);
-  // column_value_pair(const char *name, utils::database_type value);
-  // column_value_pair(const char *name, utils::placeholder p);
   column_value_pair(column_value_pair&& x) = default;
   column_value_pair& operator=(column_value_pair&& x) = default;
   column_value_pair(table_column col, column_expression_ptr expression);
@@ -24,12 +20,10 @@ public:
   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 {

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_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;
 }
 
@@ -33,7 +33,6 @@ public:
                            const sql::dialect &d,
                            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;

include/matador/query/query_builder_exception.hpp

@@ -11,7 +11,8 @@ namespace matador::query {
 
 class query_builder_exception final : public std::exception {
 public:
-  explicit query_builder_exception(error_code error, std::string &&msg);
+  explicit query_builder_exception(utils::error &&err);
+  query_builder_exception(error_code error, std::string &&msg);
 
   [[nodiscard]] const utils::error &error() const;
 

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

include/matador/query/query_utils.hpp

@@ -1,8 +1,7 @@
 #ifndef MATADOR_QUERY_UTILS_HPP
 #define MATADOR_QUERY_UTILS_HPP
 
-#include "table.hpp"
+#include "matador/utils/value.hpp"
-#include "matador/sql/dialect.hpp"
 
 #include <string>
 
@@ -11,6 +10,7 @@ class dialect;
 struct query_context;
 }
 namespace matador::query {
+class table;
 class table_column;
 
 void prepare_column(sql::query_context& ctx, const sql::dialect& d, const table_column& col);

include/matador/query/schema.hpp

@@ -318,6 +318,7 @@ public:
 
 private:
   iterator insert_table(const std::type_index& ti, const object::repository_node &node, utils::generator_type generator_type);
+  iterator insert_relation_table(const std::type_index& ti, const object::repository_node &node);
 
 private:
   template<typename Type>
@@ -352,10 +353,6 @@ utils::result<sql::query_context, utils::error> query_object_resolver_producer<T
 
 template<typename Type>
 utils::result<sql::query_context, utils::error> query_joined_object_resolver_producer<Type>::build_query(const sql::dialect &d) {
-  // producer_creator pc(repo_, typeid(Type));
-  // Type obj;
-  // access::process(pc, obj);
-
   select_query_builder qb(repo_);
   const auto *join_column = table_[collection_name()];
   const auto result = qb.build<Type>(*join_column == utils::_);
@@ -368,17 +365,18 @@ utils::result<sql::query_context, utils::error> query_joined_object_resolver_pro
 
 template <typename Type>
 void schema_observer<Type>::on_attach(const object::repository_node &node, const Type &/*prototype*/) const {
+  const object::object_info<Type>& info = node.info<Type>().get();
+  if (info.has_primary_key()) {
     primary_key_generator_finder finder;
-  const auto generator_type = finder.find(node.info<Type>().get());
+    const auto generator_type = finder.find(info);
-
     const auto it = schema_.insert_table(typeid(Type), node, generator_type);
-
-  if (!it->second.node().info().has_primary_key()) {
-    return;
-  }
-
     auto producer = std::make_unique<query_object_resolver_producer<Type>>(schema_, it->second.table(), it->second.node().info().primary_key_attribute()->name());
     schema_.resolver_producers_[typeid(Type)] = std::move(producer);
+  } else {
+    const auto it = schema_.insert_relation_table(typeid(Type), node);
+    // auto producer = std::make_unique<query_object_resolver_producer<Type>>(schema_, it->second.table(), it->second.node().info().primary_key_attribute()->name());
+    // schema_.resolver_producers_[typeid(Type)] = std::move(producer);
+  }
 }
 
 template <typename Type>

include/matador/query/schema_utils.hpp

@@ -0,0 +1,13 @@
+#ifndef MATADOR_SCHEMA_UTILS_HPP
+#define MATADOR_SCHEMA_UTILS_HPP
+
+#include "matador/query/query_contexts.hpp"
+#include "matador/query/basic_schema.hpp"
+
+namespace matador::sql {
+class dialect;
+}
+namespace matador::query {
+query_contexts to_query_contexts(const schema_node &node, const sql::dialect &d);
+}
+#endif //MATADOR_SCHEMA_UTILS_HPP

include/matador/query/session.hpp

@@ -2,6 +2,7 @@
 #define QUERY_SESSION_HPP
 
 #include "matador/query/error_code.hpp"
+#include "matador/query/delete_query_builder.hpp"
 #include "matador/query/select_query_builder.hpp"
 #include "matador/query/criteria.hpp"
 #include "matador/query/insert_query_builder.hpp"
@@ -16,6 +17,7 @@
 #include "matador/sql/statement.hpp"
 #include "matador/sql/statement_cache.hpp"
 
+#include "matador/object/object_cache.hpp"
 #include "matador/object/object_ptr.hpp"
 
 #include <unordered_map>
@@ -51,7 +53,6 @@ public:
    */
   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>
@@ -69,6 +70,8 @@ private:
   mutable sql::statement_cache cache_;
   const sql::dialect &dialect_;
 
+  object::object_cache object_cache_;
+
   const basic_schema &schema_;
   mutable std::unordered_map<std::string, std::vector<object::attribute> > prototypes_;
   std::shared_ptr<sql::resolver_service> resolver_service_;
@@ -109,12 +112,18 @@ utils::result<object::object_ptr<Type>, utils::error> session::insert(object::ob
       return utils::failure(stmt.err());
     }
 
-    if (const auto result = step->insert(*stmt); !result.is_ok()) {
+    if (const auto result = step->execute(*stmt); !result.is_ok()) {
+      return utils::failure(result.err());
+    }
+  }
+
+  // After successfully executed all inserts, add them to the object cache
+  for (auto &step : *steps) {
+    if (const auto result = step->finalize(object_cache_, resolver_service_); !result.is_ok()) {
       return utils::failure(result.err());
     }
   }
 
-  obj.change_state(object::object_state::Persistent);
   return utils::ok(obj);
 }
 
@@ -198,28 +207,67 @@ utils::result<object::object_ptr<Type>, utils::error> session::update(const obje
 
 template<typename Type>
 utils::result<void, utils::error> session::remove(const object::object_ptr<Type> &obj) {
-  const auto it = schema_.find(typeid(Type));
+  if (!obj.is_persistent()) {
-  if (it == schema_.end()) {
+    return utils::ok<void>();
+  }
+
+  if (const auto it = schema_.find(typeid(Type)); 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());
+  delete_query_builder<Type> dqb(schema_, contexts_by_type_);
-  const auto cit = contexts_by_type_.find(it->second.node().info().type_index());
+  auto steps = dqb.build(obj);
-  if (cit == contexts_by_type_.end()) {
+  if (!steps.is_ok()) {
-    return failure(make_error(error_code::UnknownType, "Failed to determine requested type."));
+    return utils::failure(make_error(error_code::FailedToBuildQuery, "Failed to build delete dependency queries."));
   }
-  auto stmt = cache_.acquire(cit->second.delete_one);
+
+  for (auto &step : *steps) {
+    const auto conn = pool_.acquire();
+    if (!conn.valid()) {
+      return utils::failure(make_error(error_code::FailedToAcquirePool, "Failed to acquire connection pool for primary key generation."));
+    }
+
+    if (const auto result = step->prepare(*conn); !result.is_ok()) {
+      return utils::failure(result.err());
+    }
+    conn.release();
+
+    auto stmt = cache_.acquire(step->ctx());
     if (!stmt.is_ok()) {
-    return failure(stmt.err());
+      return utils::failure(stmt.err());
     }
 
-  pk_object_binder binder(*stmt, stmt->bind_pos());
+    if (const auto result = step->execute(*stmt); !result.is_ok()) {
-  if (const auto update_result = binder.bind(*obj).execute(); !update_result.is_ok()) {
+      return utils::failure(result.err());
-    return utils::failure(update_result.err());
     }
+  }
+
+  // After successfully executed all deletes, add them to the object cache
+  for (auto &step : *steps) {
+    if (const auto result = step->finalize(object_cache_, resolver_service_); !result.is_ok()) {
+      return utils::failure(result.err());
+    }
+  }
+
   return utils::ok<void>();
+  // using namespace matador::utils;
+  // using namespace matador::query;
+  //
+  // const auto col = table_column(it->second.node().info().primary_key_attribute()->name());
+  // const auto cit = contexts_by_type_.find(it->second.node().info().type_index());
+  // if (cit == contexts_by_type_.end()) {
+  //   return failure(make_error(error_code::UnknownType, "Failed to determine requested type."));
+  // }
+  // auto stmt = cache_.acquire(cit->second.delete_one);
+  // if (!stmt.is_ok()) {
+  //   return failure(stmt.err());
+  // }
+  //
+  // pk_object_binder binder(*stmt, stmt->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>
@@ -233,6 +281,15 @@ utils::result<object::object_ptr<Type>, utils::error> session::find(const Primar
     return utils::failure(make_error(error_code::FailedToFindPrimaryKey, "Type hasn't primary key."));
   }
 
+  auto resolver = resolver_service_->template object_resolver<Type>();
+  if (!resolver) {
+    return utils::failure(utils::error(error_code::UnknownType, "Missing object resolver for inserted type."));
+  }
+
+  if (object_cache_.is_loaded<Type>(utils::identifier{pk})) {
+    return utils::ok(object::object_ptr(object_cache_.acquire_proxy<Type>(utils::identifier{pk}, resolver)));
+  }
+
   select_query_builder eqb(schema_);
   auto data = eqb.build<Type>(*it->second.table().primary_key_column() == pk);
   if (!data.is_ok()) {

include/matador/query/table.hpp

@@ -17,6 +17,7 @@ public:
   table(const char *name); // NOLINT(*-explicit-constructor)
   table(const std::string& name); // NOLINT(*-explicit-constructor)
   table(const std::string& name, const std::vector<table_column>& columns);
+  table(const std::string& name, const std::vector<table_column>& columns, const std::string& join_column, const std::string& inverse_join_column);
   table(const table& other);
   table& operator=(const table& other);
   table(table&& other) noexcept;
@@ -44,11 +45,11 @@ public:
   [[nodiscard]] bool has_primary_key() const;
 
   [[nodiscard]] const table_column* primary_key_column() const;
-  [[nodiscard]] const std::string& join_column_name() const;
+  [[nodiscard]] const table_column* join_column() const;
-  [[nodiscard]] const std::string& inverse_join_column_name() const;
+  [[nodiscard]] const table_column* inverse_join_column() const;
 
 protected:
-  table(std::string  name, std::string  alias, const std::vector<table_column>& columns);
+  table(std::string name, std::string  alias, const std::vector<table_column>& columns, const std::string& join_column, const std::string& inverse_join_column);
 
 private:
   friend table_column;
@@ -60,8 +61,8 @@ private:
   std::vector<table_column> columns_;
 
   int pk_column_index_{-1};
-  std::string join_column_name_;
+  int join_column_index_{-1};
-  std::string inverse_join_column_name_;
+  int inverse_join_column_index_{-1};
 };
 
 template<typename Type = table>

include/matador/sql/interface/connection_impl.hpp

@@ -5,6 +5,7 @@
 
 #include "matador/object/attribute.hpp"
 
+#include "matador/sql/dialect.hpp"
 #include "matador/sql/connection_info.hpp"
 #include "matador/sql/execute_result.hpp"
 
@@ -17,13 +18,11 @@ using blob_type_t = std::vector<unsigned char>;
 }
 
 namespace matador::sql {
-
 struct query_context;
 class query_result_impl;
 class statement_impl;
 
-class connection_impl
+class connection_impl {
-{
 public:
   virtual ~connection_impl() = default;
 

include/matador/sql/statement.hpp

@@ -3,11 +3,10 @@
 
 #include "matador/sql/abstract_sql_logger.hpp"
 #include "matador/sql/error_code.hpp"
+#include "matador/sql/execute_result.hpp"
 #include "matador/sql/query_result.hpp"
 #include "matador/sql/interface/statement_proxy.hpp"
 
-#include "matador/object/basic_repository.hpp"
-
 #include "matador/utils/error.hpp"
 #include "matador/utils/result.hpp"
 
@@ -172,7 +171,8 @@ template<class Type>
 utils::result<query_result<Type>, utils::error> statement::fetch() {
   std::cout << statement_proxy_->sql() << std::endl;
   statement_proxy_->statement_->query_.result_type = typeid(Type);
-  return statement_proxy_->fetch(*bindings_).and_then([this](std::unique_ptr<query_result_impl> &&value) {
+  return statement_proxy_->fetch(*bindings_)
+  .and_then([this](std::unique_ptr<query_result_impl> &&value) -> utils::result<query_result<Type>, utils::error> {
     auto resolver = statement_proxy_->statement_->query_.resolver->object_resolver<Type>();
     const auto prototype = value->prototype();
     return utils::ok(query_result<Type>(std::forward<decltype(value)>(value), resolver, [prototype] {

include/matador/utils/result.hpp

@@ -2,7 +2,6 @@
 #define QUERY_RESULT_HPP
 
 #include <variant>
-#include <optional>
 #include <functional>
 #include <type_traits>
 
@@ -21,6 +20,7 @@ template < typename ValueType >
 class ok {
 public:
   using value_type = ValueType;
+  constexpr ok() = default;
   explicit constexpr ok(const ValueType &value) : value_(value) {}
   explicit constexpr ok(ValueType &&value) : value_(std::move(value)) {}
 
@@ -49,21 +49,49 @@ public:
 
   constexpr ErrorType&& release() { return std::move(error_); }
   const ErrorType& value() const { return error_; }
-  ErrorType value() { return error_; }
+  ErrorType& value() { return error_; }
 
 private:
   ErrorType error_;
 };
 
+namespace detail {
+template <typename ValueType, typename Func, bool IsVoidValue = std::is_void_v<ValueType>>
+struct map_result_value_type;
+
+template <typename ValueType, typename Func>
+struct map_result_value_type<ValueType, Func, false> {
+  using type = std::invoke_result_t<Func, ValueType&&>;
+};
+
+template <typename ValueType, typename Func>
+struct map_result_value_type<ValueType, Func, true> {
+  using type = std::invoke_result_t<Func>;
+};
+
+template <typename ValueType, typename Func, bool IsVoidValue = std::is_void_v<ValueType>>
+struct and_then_result_type;
+
+template <typename ValueType, typename Func>
+struct and_then_result_type<ValueType, Func, false> {
+  using type = std::invoke_result_t<Func, ValueType&&>;
+};
+
+template <typename ValueType, typename Func>
+struct and_then_result_type<ValueType, Func, true> {
+  using type = std::invoke_result_t<Func>;
+};
+}
+
 template < typename ValueType, typename ErrorType >
 class result {
 public:
   using value_type = ValueType;
   using error_type = ErrorType;
 
-  result() : result_(ValueType{}) {}
+  result() : result_(ok<value_type>{}) {}
-  result(ok<value_type> value) : result_(std::move(value.release())) {} // NOLINT(*-explicit-constructor)
+  result(ok<value_type> value) : result_(std::move(value)) {} // NOLINT(*-explicit-constructor)
-  result(failure<error_type> error) : result_(std::move(error.release())) {} // NOLINT(*-explicit-constructor)
+  result(failure<error_type> error) : result_(std::move(error)) {} // NOLINT(*-explicit-constructor)
   result(const result &x) = default;
   result& operator=(const result &x) = default;
   result(result &&x) = default;
@@ -71,123 +99,128 @@ public:
 
   operator bool() const { return is_ok(); } // NOLINT(*-explicit-constructor)
 
-  [[nodiscard]] bool is_ok() const { return std::holds_alternative<value_type>(result_); }
+  [[nodiscard]] bool is_ok() const {
-  [[nodiscard]] bool is_error() const { return std::holds_alternative<error_type>(result_); }
+    return std::holds_alternative<ok<value_type>>(result_);
-
+  }
-  ValueType&& release() { return std::move(std::get<value_type>(result_)); }
+  [[nodiscard]] bool is_error() const {
-  ErrorType&& release_error() { return std::move(std::get<error_type>(result_)); }
+    return std::holds_alternative<failure<error_type>>(result_);
-
-  const ValueType& value() const { return std::get<value_type>(result_); }
-  ValueType& value() { return std::get<value_type>(result_); }
-  const ErrorType& err() const { return std::get<error_type>(result_); }
-  ErrorType err() { return std::get<error_type>(result_); }
-
-  constexpr const ValueType* operator->() const { return &value(); }
-  constexpr ValueType* operator->() { return &std::get<value_type>(result_); }
-
-  constexpr const ValueType& operator*() const& noexcept { return value(); }
-  constexpr ValueType& operator*() & noexcept { return value(); }
-
-  template<typename Func,
-           typename SecondValueType = std::invoke_result_t<Func, ValueType >>
-  result<SecondValueType, ErrorType> map(Func &&f) {
-    if (is_ok()) {
-      return result<SecondValueType, ErrorType>(ok(f(release())));
   }
 
-    return result<SecondValueType, ErrorType>(failure(release_error()));
+  template <typename T = ValueType>
+  std::enable_if_t<!std::is_void_v<T>, T&&> release() {
+    return std::move(std::get<ok<value_type>>(result_).release());
+  }
+  ErrorType&& release_error() {
+    return std::move(std::get<failure<error_type>>(result_).release());
+  }
+
+  template <typename T = ValueType>
+  std::enable_if_t<!std::is_void_v<T>, const T&> value() const {
+    return std::get<ok<value_type>>(result_).value();
+  }
+  template <typename T = ValueType>
+  std::enable_if_t<!std::is_void_v<T>, T&> value() {
+    return std::get<ok<value_type>>(result_).value();
+  }
+  const ErrorType& err() const {
+    return std::get<failure<error_type>>(result_).value();
+  }
+  ErrorType& err() {
+    return std::get<failure<error_type>>(result_).value();
+  }
+
+  template <typename T = ValueType>
+  constexpr std::enable_if_t<!std::is_void_v<T>, const T*> operator->() const {
+    return &value();
+  }
+  template <typename T = ValueType>
+  constexpr std::enable_if_t<!std::is_void_v<T>, T*> operator->() {
+    return &value();
+  }
+
+  template <typename T = ValueType>
+  constexpr std::enable_if_t<!std::is_void_v<T>, const T&> operator*() const& noexcept {
+    return value();
+  }
+  template <typename T = ValueType>
+  constexpr std::enable_if_t<!std::is_void_v<T>, T&> operator*() & noexcept {
+    return value();
+  }
+
+  template<typename Func,
+           typename SecondValueType = typename detail::map_result_value_type<ValueType, Func>::type>
+  result<SecondValueType, ErrorType> map(Func &&f) {
+    if (is_error()) {
+      return failure<ErrorType>(release_error());
+    }
+
+    if constexpr (std::is_void_v<ValueType>) {
+      if constexpr (std::is_void_v<SecondValueType>) {
+        std::invoke(std::forward<Func>(f));
+        return ok<void>{};
+      } else {
+        return ok<SecondValueType>(std::invoke(std::forward<Func>(f)));
+      }
+    } else {
+      if constexpr (std::is_void_v<SecondValueType>) {
+        std::invoke(std::forward<Func>(f), release());
+        return ok<void>{};
+      } else {
+        return ok<SecondValueType>(std::invoke(std::forward<Func>(f), release()));
+      }
+    }
   }
 
   template<typename Func,
            typename SecondErrorType = typename std::invoke_result_t<Func, ErrorType >::value_type>
   result<SecondErrorType, ErrorType> map_error(Func &&f) {
-    if (!is_ok()) {
+    if (!is_error()) {
-      return result<SecondErrorType, ErrorType>(ok(release()));
+      return failure<SecondErrorType>{std::invoke(std::forward<Func>(f), release_error())};
     }
 
-    return result<SecondErrorType, ErrorType>(error(release_error()));
+    if constexpr (std::is_void_v<ValueType>) {
+      return ok<void>{};
+    } else {
+      return ok<ValueType>(release());
+    }
   }
 
   template <typename Func,
-           typename SecondValueType = typename std::invoke_result_t<Func, ValueType>::value_type>
+            typename ReturnResult = typename detail::and_then_result_type<ValueType, Func>::type>
-  result<SecondValueType, ErrorType> and_then(Func &&f) {
+  ReturnResult and_then(Func &&f) {
+    static_assert(is_result<ReturnResult>::value, "and_then() callback must return matador::utils::result");
+
     if (is_ok()) {
-      return f(release());
+      if constexpr (std::is_void_v<ValueType>) {
+        return std::invoke(std::forward<Func>(f));
+      } else {
+        return std::invoke(std::forward<Func>(f), release());
+      }
     }
 
-    return result<SecondValueType, ErrorType>(failure(release_error()));
+    return ReturnResult(failure<ErrorType>(release_error()));
   }
 
   template <typename Func,
-           typename SecondErrorType = typename std::invoke_result_t<Func, ErrorType >::value_type>
+            typename FailureType = std::invoke_result_t<Func, ErrorType&&>,
+            typename SecondErrorType = typename FailureType::value_type>
   result<ValueType, SecondErrorType> or_else(Func &&f) {
     if (is_error()) {
-      return f(err());
+      return result<ValueType, SecondErrorType>(
+        std::invoke(std::forward<Func>(f), release_error())
+      );
     }
 
-    return result<ValueType, SecondErrorType>(ok(release()));
+    if constexpr (std::is_void_v<ValueType>) {
+      return ok<void>{};
+    } else {
+      return ok<ValueType>(release());
+    }
   }
 
 private:
-  std::variant<value_type, error_type> result_;
+  std::variant<ok<value_type>, failure<error_type>> result_;
 };
-
-template < typename ErrorType >
-class result<void, ErrorType>
-{
-public:
-  using value_type = void;
-  using error_type = ErrorType;
-
-  result() = default;
-  result(ok<void> /*value*/) {}
-  result(failure<error_type> error) : result_(std::move(error.release())) {} // NOLINT(*-explicit-constructor)
-  result(const result &x) = default;
-  result& operator=(const result &x) = default;
-  result(result &&x) = default;
-  result& operator=(result &&x) = default;
-
-  operator bool() const { return is_ok(); } // NOLINT(*-explicit-constructor)
-
-  [[nodiscard]] bool is_ok() const { return !result_.has_value(); }
-  [[nodiscard]] bool is_error() const { return result_.has_value(); }
-
-  ErrorType&& release_error() { return std::move(*result_); }
-
-  const ErrorType& err() const { return result_.value(); }
-  ErrorType err() { return result_.value(); }
-
-  template<typename Func, typename SecondValueType = std::invoke_result_t<Func>>
-  result<SecondValueType, ErrorType> map(Func &&f) {
-    if (is_ok()) {
-      return result<SecondValueType, ErrorType>(ok(f()));
-    }
-
-    return result<SecondValueType, ErrorType>(failure(release_error()));
-  }
-
-  template<typename Func>
-  result and_then(Func &&f) {
-    if (is_ok()) {
-      return f();
-    }
-
-    return result(failure(release_error()));
-  }
-
-  template<typename Func, typename SecondErrorType = typename std::invoke_result_t<Func, ErrorType >::value_type>
-  result<void, SecondErrorType> or_else(Func &&f) {
-    if (is_error()) {
-      return f(err());
-    }
-
-    return result<void, SecondErrorType>(ok<void>());
-  }
-
-private:
-  std::optional<error_type> result_;
-};
-
 }
 
 #endif //QUERY_RESULT_HPP

include/matador/utils/thread_pool.hpp

@@ -59,8 +59,8 @@ public:
    * @param args Passed arguments
    */
   template <typename F, typename... Args>
-  auto schedule(F&& func, Args&&... args) -> result_fut<std::result_of_t<F(cancel_token&, Args...)>> {
+  auto schedule(F&& func, Args&&... args) -> result_fut<std::invoke_result_t<F, cancel_token&, Args...>> {
-    using return_type = std::result_of_t<F(cancel_token&, Args...)>;
+    using return_type = std::invoke_result_t<F, cancel_token&, Args...>;
     const auto token = std::make_shared<cancel_token>();
 
     auto task_ptr = std::make_shared<std::packaged_task<return_type()>>(
@@ -73,7 +73,7 @@ public:
       if (!running_) {
           return failure(std::string("Thread pool is shut down, cannot schedule new tasks."));
       }
-      tasks_.emplace_back([task_ptr, token] {
+      tasks_.emplace_back([task_ptr] {
           try { (*task_ptr)(); }
           catch (...) { /* Prevent exception escape */ }
       }, token);

include/matador/utils/value.hpp

@@ -56,7 +56,7 @@ public:
     if (!res.is_ok()) {
       return std::nullopt;
     }
-    return *res;
+    return res.value();
   }
 
   template<class Type>

include/matador/utils/version.hpp

@@ -3,13 +3,13 @@
 
 #include "matador/utils/result.hpp"
 #include "matador/utils/error.hpp"
+#include "matador/utils/export.hpp"
 
 #include <string>
-#include <ostream>
 
 namespace matador::utils {
 
-class version {
+class MATADOR_UTILS_API version final {
 public:
   version() = default;
   ~version() = default;

source/core/object/attribute.cpp

@@ -32,6 +32,10 @@ std::string attribute::full_name() const {
   return owner ? owner->name() + "." + name_ : name_;
 }
 
+size_t attribute::index() const {
+  return index_;
+}
+
 const utils::field_attributes &attribute::attributes() const {
   return options_;
 }

source/core/object/basic_object_info.cpp

@@ -21,11 +21,11 @@ std::shared_ptr<class object> basic_object_info::object() const {
   return object_;
 }
 
-const std::list<attribute>& basic_object_info::attributes() const {
+const std::vector<attribute>& basic_object_info::attributes() const {
   return object_->attributes();
 }
 
-const std::list<class restriction>& basic_object_info::constraints() const {
+const std::list<restriction>& basic_object_info::constraints() const {
   return object_->constraints();
 }
 
@@ -37,7 +37,7 @@ const utils::identifier& basic_object_info::primary_key() const {
   return object_->primary_key();
 }
 
-attribute* basic_object_info::primary_key_attribute() const {
+const attribute* basic_object_info::primary_key_attribute() const {
   return object_->primary_key_attribute();
 }
 

source/core/object/basic_repository.cpp

@@ -88,7 +88,7 @@ utils::result<basic_object_info_ref, utils::error> basic_repository::basic_info(
     return utils::ok(basic_object_info_ref{it->info()});
 }
 
-utils::result<attribute*, utils::error> basic_repository::primary_key_attribute(const std::type_index &ti) const {
+utils::result<const attribute*, utils::error> basic_repository::primary_key_attribute(const std::type_index &ti) const {
   const auto it = find_node(ti);
   if (it == end()) {
     return utils::failure(make_error(error_code::NodeNotFound, "Node '" + std::string(ti.name()) + "' not found."));

source/core/object/object.cpp

@@ -10,8 +10,8 @@ const attribute& object::create_attribute(std::string name, const std::shared_pt
   return obj->attributes_.emplace_back(std::move(attr));
 }
 
-attribute* object::primary_key_attribute() const {
+const attribute* object::primary_key_attribute() const {
-  return pk_attribute_;
+  return pk_column_index_ != -1 ? &attributes_.at(pk_column_index_) : nullptr;
 }
 
 const utils::identifier& object::primary_key() const {
@@ -19,7 +19,19 @@ const utils::identifier& object::primary_key() const {
 }
 
 bool object::has_primary_key() const {
-  return pk_attribute_ != nullptr;
+  return pk_column_index_ != -1;
+}
+
+bool object::is_relation_object() const {
+  return join_column_index_ != -1 && inverse_join_column_index_ != -1;
+}
+
+const attribute * object::join_attribute() const {
+  return join_column_index_ != -1 ? &attributes_.at(join_column_index_) : nullptr;
+}
+
+const attribute * object::inverse_join_attribute() const {
+  return inverse_join_column_index_ != -1 ? &attributes_.at(inverse_join_column_index_) : nullptr;
 }
 
 const std::string& object::name() const {
@@ -38,7 +50,7 @@ size_t object::attribute_count() const {
   return attributes_.size();
 }
 
-const std::list<attribute>& object::attributes() const {
+const std::vector<attribute>& object::attributes() const {
   return attributes_;
 }
 

source/core/object/object_generator.cpp

@@ -7,7 +7,8 @@
 namespace matador::object {
 object_generator::object_generator(basic_repository &repo, const std::shared_ptr<object> &object)
 : repo_(repo)
-, object_(object) {}
+, object_(object) {
+}
 
 std::shared_ptr<object> object_generator::acquire_object(basic_repository &repo, const std::type_index &ti, const std::string &name) {
   if (repo.has_object_for_type(ti)) {
@@ -29,7 +30,7 @@ void object_generator::create_pk_constraint(const std::string& name) const {
   if (pk_attr == std::end(object_->attributes_)) {
     return;
   }
-    restriction pk_constraint(*pk_attr);
+  restriction pk_constraint(pk_attr->index());
   pk_constraint.options_ |= utils::constraints::PrimaryKey;
   pk_constraint.owner_ = object_;
   object_->constraints_.emplace_back(std::move(pk_constraint));
@@ -40,19 +41,33 @@ void object_generator::create_unique_constraint(const std::string& name) const {
   if (pk_attr == std::end(object_->attributes_)) {
     return;
   }
-    restriction pk_constraint(*pk_attr);
+  restriction pk_constraint(pk_attr->index());
   pk_constraint.options_ |= utils::constraints::Unique;
   pk_constraint.owner_ = object_;
 }
 
-std::list<attribute>::iterator object_generator::find_attribute_by_name(const std::string& name) const {
+std::vector<attribute>::iterator object_generator::find_attribute_by_name(const std::string &name) const {
   return std::find_if(std::begin(object_->attributes_), std::end(object_->attributes_), [&name](const attribute &elem) {
     return elem.name() == name;
   });
 }
 
-void object_generator::prepare_primary_key(attribute& ref, utils::identifier &&pk) const {
+void object_generator::prepare_primary_key(const attribute &ref, utils::identifier &&pk) const {
-    object_->pk_attribute_ = &ref;
+  object_->pk_column_index_ = static_cast<int>(ref.index_);
   object_->pk_identifier_ = std::move(pk);
 }
+
+void object_generator::prepare_relation_table(const std::string &join_column, const std::string &inverse_join_column) const {
+  auto it = find_attribute_by_name(join_column);
+  if (it == std::end(object_->attributes_)) {
+    return;
+  }
+  object_->join_column_index_ = static_cast<int>(it->index_);
+
+  it = find_attribute_by_name(inverse_join_column);
+  if (it == std::end(object_->attributes_)) {
+    return;
+  }
+  object_->inverse_join_column_index_ = static_cast<int>(it->index_);
+}
 }

source/core/object/restriction.cpp

@@ -4,16 +4,23 @@
 #include "matador/object/object.hpp"
 
 namespace matador::object {
-restriction::restriction(const class attribute& attr)
+restriction::restriction(const size_t attr_index)
-: attr_(attr) {}
+: index_(attr_index) {}
 
-const class attribute& restriction::attribute() const {
+size_t restriction::attribute_index() const {
-  return attr_;
+  return index_;
 }
 
 std::string restriction::column_name() const {
-  return attr_.name();
+  const auto o = owner_.lock();
+  return o ? o->attributes().at(index_).name() : "";
 }
+
+utils::constraints restriction::options() const {
+  const auto o = owner_.lock();
+  return o ? o->attributes().at(index_).attributes().options() : utils::constraints::None;
+}
+
 std::shared_ptr<object> restriction::owner() const {
   return owner_.lock();
 }

source/core/utils/version.cpp

@@ -3,98 +3,122 @@
 #include <matador/utils/errors.hpp>
 
 namespace matador::utils {
+namespace {
 
-version::version(unsigned int major, unsigned int minor, unsigned int patch)
+bool parse_uint_component(const std::string &text, std::size_t &pos, unsigned int &value) {
+  if (pos >= text.size() || text[pos] < '0' || text[pos] > '9') {
+    return false;
+  }
+
+  unsigned int result{};
+
+  while (pos < text.size() && text[pos] >= '0' && text[pos] <= '9') {
+    const auto digit = static_cast<unsigned int>(text[pos] - '0');
+
+    if (result > (std::numeric_limits<unsigned int>::max() - digit) / 10) {
+      return false;
+    }
+
+    result = result * 10 + digit;
+    ++pos;
+  }
+
+  value = result;
+  return true;
+}
+
+bool parse_dot(const std::string &text, std::size_t &pos) {
+  if (pos >= text.size() || text[pos] != '.') {
+    return false;
+  }
+
+  ++pos;
+  return true;
+}
+
+} // namespace
+version::version(const unsigned int major, const unsigned int minor, const unsigned int patch)
 : major_(major)
 , minor_(minor)
-, patch_(patch)
+, patch_(patch) {
-{}
+}
 
-bool version::operator==(const version &x) const
+bool version::operator==(const version& x) const {
-{
   return major_ == x.major_ &&
     minor_ == x.minor_ &&
     patch_ == x.patch_;
 }
 
-bool version::operator!=(const version &x) const
+bool version::operator!=(const version& x) const {
-{
   return !(*this == x);
 }
 
-bool version::operator>(const version &x) const
+bool version::operator>(const version& x) const {
-{
   return !(*this <= x);
 }
 
-bool version::operator>=(const version &x) const
+bool version::operator>=(const version& x) const {
-{
   return !(*this < x);
 }
 
-bool version::operator<(const version &x) const
+bool version::operator<(const version& x) const {
-{
   return (major_ < x.major_) ||
     (major_ == x.major_ && minor_ < x.minor_) ||
     (major_ == x.major_ && minor_ == x.minor_ && patch_ < x.patch_);
 }
 
-bool version::operator<=(const version &x) const
+bool version::operator<=(const version& x) const {
-{
   return *this < x || *this == x;
 }
 
-std::string version::str() const
+std::string version::str() const {
-{
+  return std::to_string(major_) + "." +
-  char buf[32];
+    std::to_string(minor_) + "." +
-  sprintf(buf, "%d.%d.%d", major_, minor_, patch_);
+    std::to_string(patch_);
-  return buf;
 }
 
-std::ostream &operator<<(std::ostream &out, const version &v)
+std::ostream& operator<<(std::ostream& out, const version& v) {
-{
   out << v.str();
   return out;
 }
 
-result<version, error> version::from_string(const std::string &version_string)
+result<version, error> version::from_string(const std::string& version_string) {
-{
+  unsigned int major{};
-  version result;
+  unsigned int minor{};
-  if (const auto ret = sscanf(version_string.c_str(), "%u.%u.%u", &result.major_, &result.minor_, &result.patch_); ret != 3) {
+  unsigned int patch{};
+
+  if (std::size_t pos{}; !parse_uint_component(version_string, pos, major) ||
+      !parse_dot(version_string, pos) ||
+      !parse_uint_component(version_string, pos, minor) ||
+      !parse_dot(version_string, pos) ||
+      !parse_uint_component(version_string, pos, patch) ||
+      pos != version_string.size()) {
     return failure(error(utils_error::InvalidVersionString, version_string));
       }
 
-  return ok(result);
+  return ok(version{major, minor, patch});}
-}
 
-unsigned int version::major() const
+unsigned int version::major() const {
-{
   return major_;
 }
 
-unsigned int version::minor() const
+unsigned int version::minor() const {
-{
   return minor_;
 }
 
-unsigned int version::patch() const
+unsigned int version::patch() const {
-{
   return patch_;
 }
 
-void version::major(unsigned int m)
+void version::major(unsigned int m) {
-{
   major_ = m;
 }
 
-void version::minor(unsigned int m)
+void version::minor(unsigned int m) {
-{
   minor_ = m;
 }
 
-void version::patch(unsigned int p)
+void version::patch(unsigned int p) {
-{
   patch_ = p;
 }
-
 }

source/orm/CMakeLists.txt

@@ -16,7 +16,10 @@ add_library(matador-orm STATIC
   ../../include/matador/query/criteria/logical_criteria.hpp
   ../../include/matador/query/criteria_evaluator.hpp
   ../../include/matador/query/database.hpp
+  ../../include/matador/query/delete_query_builder.hpp
+  ../../include/matador/query/delete_step.hpp
   ../../include/matador/query/error_code.hpp
+  ../../include/matador/query/execute_step.hpp
   ../../include/matador/query/expression/abstract_column_expression.hpp
   ../../include/matador/query/expression/binary_column_expression.hpp
   ../../include/matador/query/expression/column_expression.hpp
@@ -68,9 +71,9 @@ add_library(matador-orm STATIC
   ../../include/matador/query/key_value_generator.hpp
   ../../include/matador/query/manual_pk_generator.hpp
   ../../include/matador/query/meta_table_macro.hpp
-  ../../include/matador/query/meta_table_macro.hpp
   ../../include/matador/query/query.hpp
   ../../include/matador/query/query_builder.hpp
+  ../../include/matador/query/query_builder_utils.hpp
   ../../include/matador/query/query_collection_resolver.hpp
   ../../include/matador/query/query_column.hpp
   ../../include/matador/query/query_contexts.hpp
@@ -80,6 +83,7 @@ add_library(matador-orm STATIC
   ../../include/matador/query/query_part.hpp
   ../../include/matador/query/query_utils.hpp
   ../../include/matador/query/schema.hpp
+  ../../include/matador/query/schema_utils.hpp
   ../../include/matador/query/select_query_builder.hpp
   ../../include/matador/query/sequence_pk_generator.hpp
   ../../include/matador/query/session.hpp
@@ -104,9 +108,9 @@ add_library(matador-orm STATIC
   ../../include/matador/sql/interface/query_result_reader.hpp
   ../../include/matador/sql/interface/statement_impl.hpp
   ../../include/matador/sql/interface/statement_proxy.hpp
-  ../../include/matador/sql/internal/joined_collection_resolver_producer.hpp
   ../../include/matador/sql/internal/identifier_reader.hpp
   ../../include/matador/sql/internal/identifier_statement_binder.hpp
+  ../../include/matador/sql/internal/joined_collection_resolver_producer.hpp
   ../../include/matador/sql/internal/object_resolver_producer.hpp
   ../../include/matador/sql/internal/object_result_binder.hpp
   ../../include/matador/sql/internal/pk_reader.hpp
@@ -188,6 +192,7 @@ add_library(matador-orm STATIC
   query/query_part.cpp
   query/query_utils.cpp
   query/schema.cpp
+  query/schema_utils.cpp
   query/select_query_builder.cpp
   query/sequence_pk_generator.cpp
   query/session.cpp
@@ -208,9 +213,9 @@ add_library(matador-orm STATIC
   sql/interface/query_result_reader.cpp
   sql/interface/statement_impl.cpp
   sql/interface/statement_proxy.cpp
-  sql/internal/joined_collection_resolver_producer.cpp
   sql/internal/identifier_reader.cpp
   sql/internal/identifier_statement_binder.cpp
+  sql/internal/joined_collection_resolver_producer.cpp
   sql/internal/object_resolver_producer.cpp
   sql/internal/object_result_binder.cpp
   sql/internal/query_result_pk_resolver.cpp

source/orm/query/attribute_string_writer.cpp

@@ -2,7 +2,6 @@
 
 #include "matador/query/query_utils.hpp"
 
-#include "matador/sql/interface/connection_impl.hpp"
 #include "matador/sql/dialect.hpp"
 
 #include <matador/utils/convert.hpp>

source/orm/query/criteria/criteria_operators.cpp

@@ -13,61 +13,61 @@ namespace matador::query {
 criteria_ptr operator==(const table_column &col, const utils::identifier &id) {
   utils::identifier_to_value_converter conv;
 
-  return std::make_unique<binary_criteria>(col, binary_operator::EQUALS, conv.convert(id));
+  return std::make_unique<binary_criteria>(col, binary_operator::Equals, conv.convert(id));
 }
 
 criteria_ptr operator!=(const table_column &col, const utils::identifier &id) {
   utils::identifier_to_value_converter conv;
 
-  return std::make_unique<binary_criteria>(col, binary_operator::NOT_EQUALS, conv.convert(id));
+  return std::make_unique<binary_criteria>(col, binary_operator::NotEquals, conv.convert(id));
 }
 
 criteria_ptr operator==(const table_column &col, utils::placeholder p) {
-  return std::make_unique<binary_criteria>(col, binary_operator::EQUALS, p);
+  return std::make_unique<binary_criteria>(col, binary_operator::Equals, p);
 }
 
 criteria_ptr operator!=(const table_column &col, utils::placeholder p) {
-  return std::make_unique<binary_criteria>(col, binary_operator::NOT_EQUALS, p);
+  return std::make_unique<binary_criteria>(col, binary_operator::NotEquals, p);
 }
 
 criteria_ptr operator>(const table_column &col, utils::placeholder p) {
-  return std::make_unique<binary_criteria>(col, binary_operator::GREATER_THAN, p);
+  return std::make_unique<binary_criteria>(col, binary_operator::GreaterThan, p);
 }
 
 criteria_ptr operator>=(const table_column &col, utils::placeholder p) {
-  return std::make_unique<binary_criteria>(col, binary_operator::GREATER_THAN_OR_EQUAL, p);
+  return std::make_unique<binary_criteria>(col, binary_operator::GreaterThanOrEqual, p);
 }
 
 criteria_ptr operator<(const table_column &col, utils::placeholder p) {
-  return std::make_unique<binary_criteria>(col, binary_operator::LESS_THAN, p);
+  return std::make_unique<binary_criteria>(col, binary_operator::LessThan, p);
 }
 
 criteria_ptr operator<=(const table_column &col, utils::placeholder p) {
-  return std::make_unique<binary_criteria>(col, binary_operator::LESS_THAN_OR_EQUAL, p);
+  return std::make_unique<binary_criteria>(col, binary_operator::LessThanOrEqual, p);
 }
 
 criteria_ptr operator==( const table_column& col_left, const table_column& col_right ) {
-    return std::make_unique<binary_column_criteria>(col_left, binary_operator::EQUALS, col_right);
+    return std::make_unique<binary_column_criteria>(col_left, binary_operator::Equals, col_right);
 }
 
 criteria_ptr operator!=( const table_column& col_left, const table_column& col_right ) {
-    return std::make_unique<binary_column_criteria>(col_left, binary_operator::NOT_EQUALS, col_right);
+    return std::make_unique<binary_column_criteria>(col_left, binary_operator::NotEquals, col_right);
 }
 
 criteria_ptr operator>( const table_column& col_left, const table_column& col_right ) {
-    return std::make_unique<binary_column_criteria>(col_left, binary_operator::GREATER_THAN, col_right);
+    return std::make_unique<binary_column_criteria>(col_left, binary_operator::GreaterThan, col_right);
 }
 
 criteria_ptr operator>=( const table_column& col_left, const table_column& col_right ) {
-    return std::make_unique<binary_column_criteria>(col_left, binary_operator::GREATER_THAN_OR_EQUAL, col_right);
+    return std::make_unique<binary_column_criteria>(col_left, binary_operator::GreaterThanOrEqual, col_right);
 }
 
 criteria_ptr operator<( const table_column& col_left, const table_column& col_right ) {
-    return std::make_unique<binary_column_criteria>(col_left, binary_operator::LESS_THAN, col_right);
+    return std::make_unique<binary_column_criteria>(col_left, binary_operator::LessThan, col_right);
 }
 
 criteria_ptr operator<=( const table_column& col_left, const table_column& col_right ) {
-    return std::make_unique<binary_column_criteria>(col_left, binary_operator::LESS_THAN_OR_EQUAL, col_right);
+    return std::make_unique<binary_column_criteria>(col_left, binary_operator::LessThanOrEqual, col_right);
 }
 
 criteria_ptr operator&&(criteria_ptr left, criteria_ptr right) {

source/orm/query/criteria_evaluator.cpp

@@ -18,12 +18,12 @@
 namespace matador::query {
 namespace detail {
 static const utils::enum_mapper<binary_operator> BinaryOperatorEnum({
-  {binary_operator::EQUALS, "="},
+  {binary_operator::Equals, "="},
-  {binary_operator::NOT_EQUALS, "<>"},
+  {binary_operator::NotEquals, "<>"},
-  {binary_operator::GREATER_THAN, ">"},
+  {binary_operator::GreaterThan, ">"},
-  {binary_operator::GREATER_THAN_OR_EQUAL, ">="},
+  {binary_operator::GreaterThanOrEqual, ">="},
-  {binary_operator::LESS_THAN, "<"},
+  {binary_operator::LessThan, "<"},
-  {binary_operator::LESS_THAN_OR_EQUAL, "<="},
+  {binary_operator::LessThanOrEqual, "<="},
 });
 }
 

source/orm/query/intermediates/executable_query.cpp

@@ -22,9 +22,8 @@ sql::query_context executable_query::compile(const sql::dialect& d) const {
   return compiler.build(*context_, d, std::nullopt);
 }
 
-std::string executable_query::str(const sql::executor &exec) const {
+std::string executable_query::str(const sql::dialect& d) const {
-  query_builder compiler;
+  return compile(d).sql;
-  return exec.str(compiler.build(*context_, exec.dialect(), std::nullopt));
 }
 
 }

source/orm/query/intermediates/fetchable_query.cpp

@@ -30,7 +30,7 @@ utils::result<sql::query_result<sql::record>, utils::error> fetchable_query::fet
   auto ctx = compiler.build(*context_, exec.dialect(), std::nullopt);
   ctx.resolver = exec.resolver();
   return exec.fetch(ctx)
-    .and_then([](auto &&res) {
+    .and_then([](auto &&res) -> utils::result<sql::query_result<sql::record>, utils::error> {
       const auto prototype = res->prototype();
       return utils::ok(sql::query_result<sql::record>(std::forward<decltype(res)>(res), prototype));
     });
@@ -55,9 +55,6 @@ utils::result<std::optional<sql::record>, utils::error> fetchable_query::fetch_o
   return utils::ok(std::optional{first.release()});
 }
 
-std::string fetchable_query::str(const sql::executor &exec) const {
-  return str(exec.dialect());
-}
 std::string fetchable_query::str(const sql::dialect &d) const {
   return compile(d).sql;
 }

source/orm/query/intermediates/query_alter_table_intermediate.cpp

@@ -33,7 +33,7 @@ query_add_foreign_key_constraint_intermediate query_add_key_constraint_intermedi
 
 executable_query query_alter_table_intermediate::add_constraint(const object::restriction &rest) {
   context_->parts.push_back(std::make_unique<internal::query_add_constraint_part_by_constraint>(
-    table_constraint{rest.column_name(), rest.owner()->name(), rest.attribute().attributes().options(), rest.ref_table_name(), rest.ref_column_name()}
+    table_constraint{rest.column_name(), rest.owner()->name(), rest.options(), rest.ref_table_name(), rest.ref_column_name()}
   ));
 
   return {context_};
@@ -47,7 +47,7 @@ query_add_key_constraint_intermediate query_alter_table_intermediate::add_constr
 
 executable_query query_alter_table_intermediate::drop_constraint(const object::restriction &rest) {
   context_->parts.push_back(std::make_unique<internal::query_drop_key_constraint_part_by_constraint>(
-    table_constraint{rest.column_name(), rest.owner()->name(), rest.attribute().attributes().options(), rest.ref_table_name(), rest.ref_column_name()})
+    table_constraint{rest.column_name(), rest.owner()->name(), rest.options(), rest.ref_table_name(), rest.ref_column_name()})
   );
   return {context_};
 }

source/orm/query/intermediates/query_create_intermediate.cpp

@@ -46,11 +46,11 @@ executable_query query_create_table_columns_intermediate::constraints(const std:
   std::list<table_constraint> constraints;
   for (const auto& restr : restrictions) {
     if (restr.is_primary_key_constraint()) {
-      constraints.emplace_back(restr.column_name(), restr.owner()->name(), restr.attribute().attributes().options());
+      constraints.emplace_back(restr.column_name(), restr.owner()->name(), restr.options());
     } else if (restr.is_foreign_key_constraint()) {
-      constraints.emplace_back(restr.column_name(), restr.owner()->name(), restr.attribute().attributes().options(), restr.ref_table_name(), restr.ref_column_name());
+      constraints.emplace_back(restr.column_name(), restr.owner()->name(), restr.options(), restr.ref_table_name(), restr.ref_column_name());
     } else if (restr.is_unique_constraint()) {
-      constraints.emplace_back(restr.column_name(), restr.owner()->name(), restr.attribute().attributes().options());
+      constraints.emplace_back(restr.column_name(), restr.owner()->name(), restr.options());
     }
   }
   context_->parts.push_back(std::make_unique<internal::query_create_table_constraints_part>(constraints));
@@ -58,10 +58,10 @@ executable_query query_create_table_columns_intermediate::constraints(const std:
 }
 
 query_create_table_columns_intermediate query_create_table_intermediate::columns(const std::initializer_list<object::attribute> attributes) {
-  return columns(std::list(attributes));
+  return columns(std::vector(attributes));
 }
 
-query_create_table_columns_intermediate query_create_table_intermediate::columns(const std::list<object::attribute>& attributes) {
+query_create_table_columns_intermediate query_create_table_intermediate::columns(const std::vector<object::attribute>& attributes) {
   std::list<table_column> columns;
   for (const auto& attr : attributes) {
     auto options = attr.attributes().options();

source/orm/query/internal/column_value_pair.cpp

@@ -3,26 +3,6 @@
 #include <utility>
 
 namespace matador::query::internal {
-
-// column_value_pair::column_value_pair(const std::string& name, utils::database_type value)
-// : column_(name)
-// , value_(std::move(value)) {
-// }
-//
-// column_value_pair::column_value_pair(table_column col, utils::database_type value)
-// : column_(std::move(col))
-// , value_(std::move(value)) {
-// }
-//
-// column_value_pair::column_value_pair(const char *name, utils::database_type value)
-// : column_(name)
-// , value_(std::move(value)) {
-// }
-//
-// column_value_pair::column_value_pair( const char* name, utils::placeholder p )
-// : column_(name)
-// , value_(p) {}
-
 column_value_pair::column_value_pair(table_column col, column_expression_ptr expression)
 : column_(std::move(col))
 , expression_(std::move(expression)){
@@ -32,10 +12,6 @@ const table_column &column_value_pair::col() const {
   return column_;
 }
 
-// const std::variant<utils::placeholder, utils::database_type>& column_value_pair::value() const {
-  // return value_;
-// }
-
 const abstract_column_expression& column_value_pair::expression() const {
   return *expression_;
 }

source/orm/query/query_builder.cpp

@@ -12,8 +12,6 @@
 #include "matador/query/internal/string_builder_utils.hpp"
 #include "matador/query/internal/query_parts.hpp"
 
-#include "matador/sql/interface/connection_impl.hpp"
-
 #include "matador/sql/query_context.hpp"
 #include "matador/sql/dialect.hpp"
 

source/orm/query/query_builder_exception.cpp

@@ -1,6 +1,8 @@
 #include "matador/query/query_builder_exception.hpp"
 
 namespace matador::query {
+query_builder_exception::query_builder_exception(utils::error &&err)
+: error_(std::move(err)) {}
 
 query_builder_exception::query_builder_exception(const error_code error, std::string&& msg)
 : error_(error, msg)

source/orm/query/schema.cpp

@@ -59,4 +59,19 @@ schema::iterator schema::insert_table(const std::type_index &ti, const object::r
   }
   return schema_nodes_.insert({ti, schema_node{table(node.name(), columns), std::move(pk_generator), node}}).first;
 }
+
+basic_schema::iterator schema::insert_relation_table(const std::type_index &ti, const object::repository_node &node) {
+  std::vector<table_column> columns;
+  const auto* attr = node.info().object()->join_attribute();
+  if (attr == nullptr) {
+    return schema_nodes_.end();
+  }
+  columns.emplace_back(nullptr, attr->name(), attr->type(), attr->attributes());
+  attr = node.info().object()->inverse_join_attribute();
+  if (attr == nullptr) {
+    return schema_nodes_.end();
+  }
+  columns.emplace_back(nullptr, attr->name(), attr->type(), attr->attributes());
+  return schema_nodes_.insert({ti, schema_node{table(node.name(), columns, node.info().object()->join_attribute()->name(), node.info().object()->inverse_join_attribute()->name()), nullptr, node}}).first;
+}
 } // namespace matador::query

source/orm/query/schema_utils.cpp

@@ -0,0 +1,62 @@
+#include "matador/query/schema_utils.hpp"
+#include "matador/query/query.hpp"
+#include "matador/query/criteria.hpp"
+
+using namespace matador::utils;
+
+namespace matador::query {
+query_contexts to_query_contexts(const schema_node& node, const sql::dialect &d) {
+  query_contexts queries;
+
+  // SELECT all
+  queries.select_all = select(node.table())
+    .from(node.name())
+    .compile(d);
+  if (node.table().has_primary_key()) {
+    // SELECT one
+    queries.select_one = select(node.table())
+      .from(node.name())
+      .where(*node.table().primary_key_column() == _)
+      .compile(d);
+    // UPDATE one
+    auto update_set = query::update(node.table());
+    for (const auto &col: node.table().columns()) {
+      update_set.set(col, _);
+    }
+    queries.update_one = update_set.where(*node.table().primary_key_column() == _)
+      .compile(d);
+    // DELETE one
+    queries.delete_one = query::remove()
+      .from(node.name())
+      .where(*node.table().primary_key_column() == _)
+      .compile(d);
+  } else {
+    queries.delete_one = query::remove()
+      .from(node.name())
+      .where(*node.table().join_column() == _ && *node.table().inverse_join_column() == _)
+      .compile(d);
+  }
+  // INSERT one
+  std::vector<table_column> columns;
+  for (const auto &col: node.table().columns()) {
+    if (col.is_primary_key() && utils::is_constraint_set(col.attributes().options(), constraints::Identity)) {
+      continue;
+    }
+    columns.push_back(col);
+  }
+  if (node.table().has_primary_key() && node.pk_generator().type() == generator_type::Identity) {
+    queries.insert = query::insert()
+      .into(node.name(), columns)
+      .values(generator::placeholders(columns.size()))
+      .returning(node.table().primary_key_column()->as(node.table().primary_key_column()->column_name()))
+      .compile(d);
+  } else {
+    queries.insert = query::insert()
+      .into(node.name(), columns)
+      .values(generator::placeholders(columns.size()))
+      .compile(d);
+  }
+
+  return queries;
+}
+}

source/orm/query/select_query_builder.cpp

@@ -83,7 +83,7 @@ void select_query_builder::append_join(const table_column &left, const table_col
   using namespace matador::query;
   entity_query_data_.joins.push_back({
     right.table(),
-    std::make_unique<binary_column_criteria>(left, binary_operator::EQUALS, right)
+    std::make_unique<binary_column_criteria>(left, binary_operator::Equals, right)
   });
 }
 }

source/orm/query/session.cpp

@@ -3,9 +3,8 @@
 #include "matador/sql/backend_provider.hpp"
 #include "matador/sql/dialect.hpp"
 
-#include "matador/query/query.hpp"
-#include "matador/query/generator.hpp"
 #include "matador/query/basic_schema.hpp"
+#include "matador/query/schema_utils.hpp"
 
 #include <stdexcept>
 
@@ -18,55 +17,12 @@ session::session(session_context&& ctx, const basic_schema &scm)
 : pool_(ctx.dns, ctx.connection_count, [ctx](const sql::connection_info& info) { return sql::connection(info, ctx.resolver_service); })
 , cache_(ctx.bus, pool_, ctx.cache_size)
 , dialect_(sql::backend_provider::instance().connection_dialect(pool_.info().type))
+, object_cache_(ctx.bus)
 , schema_(scm)
 , resolver_service_(ctx.resolver_service) {
   using namespace matador::utils;
   for (const auto &[type, node] : schema_) {
-    query_contexts queries;
+    query_contexts queries = to_query_contexts(node, dialect_);
-
-    // SELECT all
-    queries.select_all = select(node.table())
-      .from(node.name())
-      .compile(dialect_);
-    if (node.table().has_primary_key()) {
-      // SELECT one
-      queries.select_one = select(node.table())
-        .from(node.name())
-        .where(*node.table().primary_key_column() == _)
-        .compile(dialect_);
-      // UPDATE one
-      auto update_set = query::update(node.table());
-      for (const auto &col: node.table().columns()) {
-        update_set.set(col, _);
-      }
-      queries.update_one = update_set.where(*node.table().primary_key_column() == _)
-        .compile(dialect_);
-      // DELETE one
-      queries.delete_one = query::remove()
-        .from(node.name())
-        .where(*node.table().primary_key_column() == _)
-        .compile(dialect_);
-    }
-    // INSERT one
-    std::vector<table_column> columns;
-    for (const auto &col: node.table().columns()) {
-      if (col.is_primary_key() && utils::is_constraint_set(col.attributes().options(), constraints::Identity)) {
-        continue;
-      }
-      columns.push_back(col);
-    }
-    if (node.pk_generator().type() == utils::generator_type::Identity) {
-      queries.insert = query::insert()
-        .into(node.name(), columns)
-        .values(generator::placeholders(columns.size()))
-        .returning(node.table().primary_key_column()->as(node.table().primary_key_column()->column_name()))
-        .compile(dialect_);
-    } else {
-      queries.insert = query::insert()
-        .into(node.name(), columns)
-        .values(generator::placeholders(columns.size()))
-        .compile(dialect_);
-    }
 
     queries.insert.resolver = resolver_service_;
     queries.update_one.resolver = resolver_service_;

source/orm/query/table.cpp

@@ -9,13 +9,17 @@ table::table(const char* name)
 {}
 
 table::table(const std::string& name)
-: table(name, name, {}) {}
+: table(name, name, {}, {}, {}) {}
 
 table::table(const std::string& name, const std::vector<table_column> &columns)
-: table(name, name, columns) {
+: table(name, name, columns, {}, {}) {
 }
 
-table::table(std::string name, std::string alias, const std::vector<table_column> &columns)
+table::table(const std::string& name, const std::vector<table_column>& columns, const std::string& join_column, const std::string& inverse_join_column)
+: table(name, name, columns, join_column, inverse_join_column) {
+}
+
+table::table(std::string name, std::string alias, const std::vector<table_column> &columns, const std::string& join_column, const std::string& inverse_join_column)
 : name_(std::move(name))
 , alias_(std::move(alias))
 , columns_(columns) {
@@ -24,6 +28,12 @@ table::table(std::string name, std::string alias, const std::vector<table_column
     if (columns_[i].is_primary_key()) {
       pk_column_index_ = i;
     }
+    if (columns_[i].column_name() == join_column) {
+      join_column_index_ = i;
+    }
+    if (columns_[i].column_name() == inverse_join_column) {
+      inverse_join_column_index_ = i;
+    }
   }
 }
 
@@ -32,7 +42,9 @@ table::table(const table &other)
 , alias_(other.alias_)
 , schema_name_(other.schema_name_)
 , columns_(other.columns_)
-, pk_column_index_(other.pk_column_index_){
+, pk_column_index_(other.pk_column_index_)
+, join_column_index_(other.join_column_index_)
+, inverse_join_column_index_(other.inverse_join_column_index_) {
   for (auto &col : columns_) {
     col.table(this);
   }
@@ -54,6 +66,8 @@ table & table::operator=(table &&other) noexcept {
   alias_ = std::move(other.alias_);
   columns_ = std::move(other.columns_);
   pk_column_index_ = other.pk_column_index_;
+  join_column_index_ = other.join_column_index_;
+  inverse_join_column_index_ = other.inverse_join_column_index_;
   for (auto &col : columns_) {
     col.table(this);
   }
@@ -65,7 +79,7 @@ bool table::operator==(const table& x) const {
 }
 
 table table::as(const std::string &alias) const {
-  return { name_, alias, columns_ };
+  return { name_, alias, columns_, join_column_index_ > -1 ? join_column()->name() : std::string{}, inverse_join_column_index_ > -1 ? inverse_join_column()->name() : std::string{}};
 }
 
 const std::string & table::table_name() const {
@@ -121,11 +135,11 @@ const table_column* table::primary_key_column() const {
   return pk_column_index_ > -1 ? &columns_.at(pk_column_index_) : nullptr;
 }
 
-const std::string &table::join_column_name() const {
+const table_column* table::join_column() const {
-  return join_column_name_;
+  return join_column_index_ > -1 ? &columns_.at(join_column_index_) : nullptr;
 }
 
-const std::string &table::inverse_join_column_name() const {
+const table_column* table::inverse_join_column() const {
-  return inverse_join_column_name_;
+  return inverse_join_column_index_ > -1 ? &columns_.at(inverse_join_column_index_) : nullptr;
 }
 }

test/backends/QueryFixture.cpp

@@ -37,7 +37,8 @@ void QueryFixture::check_table_not_exists(const std::string &table_name) const {
 }
 
 void QueryFixture::drop_table_if_exists(const std::string &table_name) const {
-  const auto result = db.exists(table_name).and_then([&table_name, this](const bool exists) {
+  const auto result = db.exists(table_name)
+  .and_then([&table_name, this](const bool exists) -> utils::result<bool, utils::error> {
     if (exists) {
       auto res = query::drop()
         .table(table_name)

test/backends/SequenceFixture.cpp

@@ -35,7 +35,8 @@ void SequenceFixture::check_sequence_not_exists(const std::string& sequence_name
 }
 
 void SequenceFixture::drop_sequence_if_exists(const std::string& sequence_name) const {
-  const auto result = db.sequence_exists(sequence_name).and_then([&sequence_name, this](const bool exists) {
+  const auto result = db.sequence_exists(sequence_name).
+  and_then([&sequence_name, this](const bool exists) -> utils::result<bool, utils::error> {
     if (exists) {
       auto res = query::drop()
         .sequence(sequence_name)

test/backends/SessionDeleteHasMany.cpp

@@ -0,0 +1,75 @@
+#include "catch2/catch_test_macros.hpp"
+
+#include "SessionFixture.hpp"
+
+#include "connection.hpp"
+
+#include "matador/query/session.hpp"
+
+#include "models/author.hpp"
+#include "models/book.hpp"
+
+using namespace matador::test;
+using namespace matador::query;
+using namespace matador::object;
+
+namespace matador::test {
+template<typename AuthorType>
+void validate_author_state(const object_ptr<AuthorType>& ptr, object_state expected_state) {
+  REQUIRE(ptr.is_state(expected_state));
+  for (auto &b: ptr->books) {
+    REQUIRE(b.is_state(expected_state));
+  }
+}
+}
+
+namespace matador::utils {
+template < typename ValueType >
+std::ostream& operator<<(std::ostream& os, const result<ValueType, error>& value) {
+  if (value) {
+    return os;
+  }
+  return os << "Error: " << value.err();
+}
+
+std::ostream& operator<<(std::ostream& os, const result<void, error>& value) {
+  if (value) {
+    return os;
+  }
+  return os << "Error: " << value.err();
+}
+}
+
+TEST_CASE_METHOD(SessionFixture, "Test delete object with has many relation", "[session][delete][has_many]") {
+  const auto result = schema.attach<book>("books")
+    .and_then( [this] { return schema.attach<author>("authors"); } )
+    .and_then([this] { return schema.create(db); } );
+  REQUIRE(result.is_ok());
+
+  session ses({bus, connection::dns, 4}, schema);
+
+  auto s_king = make_object<author>(1, "Steven", "King", "21.9.1947", 1956, false);
+
+  s_king->books.push_back(make_object<book>(2, "Carrie", nullobj, 1974));
+  s_king->books.push_back(make_object<book>(3, "The Shining", nullobj, 1977));
+  s_king->books.push_back(make_object<book>(4, "It", nullobj, 1986));
+  s_king->books.push_back(make_object<book>(5, "Misery", nullobj, 1987));
+  s_king->books.push_back(make_object<book>(6, "The Dark Tower: The Gunslinger", nullobj, 1982));
+
+  validate_author_state(s_king, object_state::Transient);
+  auto res = ses.insert(s_king);
+  REQUIRE(res);
+  validate_author_state(s_king, object_state::Persistent);
+
+  auto author_result = ses.find<author>(s_king->id);
+  REQUIRE(author_result);
+  REQUIRE(author_result->is_persistent());
+  REQUIRE(author_result.value()->books.size() == 5);
+
+  const auto id = s_king->id;
+  auto del_res = ses.remove(s_king);
+  REQUIRE(del_res);
+
+  author_result = ses.find<author>(id);
+  REQUIRE_FALSE(author_result);
+}

test/backends/SessionDeleteHasManyToMany.cpp

@@ -0,0 +1,69 @@
+#include "catch2/catch_test_macros.hpp"
+
+#include "SessionFixture.hpp"
+
+#include "connection.hpp"
+
+#include "matador/query/session.hpp"
+
+#include "models/recipe.hpp"
+
+using namespace matador::test;
+using namespace matador::query;
+using namespace matador::object;
+
+namespace matador::test {
+template<typename AuthorType>
+void validate_author_state(const object_ptr<AuthorType>& ptr, object_state expected_state) {
+  REQUIRE(ptr.is_state(expected_state));
+  for (auto &b: ptr->books) {
+    REQUIRE(b.is_state(expected_state));
+  }
+}
+}
+
+TEST_CASE_METHOD(SessionFixture, "Test delete object with has many to many relation", "[session][delete][has_many_to_many]") {
+  auto result = schema.attach<recipe_sequence>("recipes")
+    .and_then( [this] { return schema.attach<ingredient_sequence>("ingredients"); } )
+    .and_then([this] { return schema.create(db); } );
+
+  session ses({bus, connection::dns, 4}, schema);
+
+  std::vector ingredients {
+    make_object<ingredient_sequence>("Apple"),
+    make_object<ingredient_sequence>("Strawberry"),
+    make_object<ingredient_sequence>("Pineapple"),
+    make_object<ingredient_sequence>("Sugar"),
+    make_object<ingredient_sequence>("Flour"),
+    make_object<ingredient_sequence>("Butter"),
+    make_object<ingredient_sequence>("Beans")
+  };
+
+  std::vector recipes {
+    make_object<recipe_sequence>("Apple Pie", std::vector{ingredients[0], ingredients[3], ingredients[4]}),
+    make_object<recipe_sequence>("Strawberry Cake", std::vector{ingredients[5], ingredients[6]}),
+    make_object<recipe_sequence>("Pineapple Pie", std::vector{ingredients[0], ingredients[1], ingredients[2]})
+  };
+
+  for (auto &r: recipes) {
+    REQUIRE(r.is_transient());
+    auto res = ses.insert(r);
+    REQUIRE(res.is_ok());
+    REQUIRE(res->is_persistent());
+  }
+
+  auto recipe_result = ses.find<recipe_sequence>(1);
+  REQUIRE(recipe_result.is_ok());
+  REQUIRE(recipe_result->is_persistent());
+  REQUIRE(recipe_result.value()->ingredients.size() == 3);
+
+  const auto ing_result = ses.find<ingredient_sequence>(ingredients[0]->id);
+  REQUIRE(ing_result.is_ok());
+  REQUIRE(ing_result.value()->recipes.size() == 2);
+
+  auto del_res = ses.remove(recipes[0]);
+  REQUIRE(del_res);
+
+  recipe_result = ses.find<recipe_sequence>(1);
+  REQUIRE_FALSE(recipe_result);
+}

test/backends/SessionInsertBelongsTo.cpp

@@ -25,7 +25,8 @@ TEST_CASE_METHOD(SessionFixture, "Test insert object with belongs to relation wi
   const auto carrie = make_object<book_identity>("Carrie", s_king, 1974);
 
   REQUIRE(carrie.is_transient());
-  REQUIRE(ses.insert(carrie).is_ok());
+  const auto res = ses.insert(carrie);
+  REQUIRE(res.is_ok());
   REQUIRE(carrie.is_persistent());
 
   auto found_author = ses.find<author_identity>(s_king->id);

test/backends/SessionInsertHasMany.cpp

@@ -61,6 +61,16 @@ void validate_author_state(const object_ptr<AuthorType>& ptr, object_state expec
   }
 }
 
+namespace matador::utils {
+template < typename ValueType >
+std::ostream& operator<<(std::ostream& os, const result<ValueType, error>& value) {
+  if (value) {
+    return os;
+  }
+  return os << "Error: " << value.err();
+}
+}
+
 TEST_CASE_METHOD(SessionFixture, "Test insert object with has many relation", "[session][insert][has_many]") {
   const auto result = schema.attach<book>("books")
     .and_then( [this] { return schema.attach<author>("authors"); } )
@@ -69,6 +79,7 @@ TEST_CASE_METHOD(SessionFixture, "Test insert object with has many relation", "[
 
   session ses({bus, connection::dns, 4}, schema);
 
+  {
     auto s_king = make_object<author>(1, "Steven", "King", "21.9.1947", 1956, false);
 
     s_king->books.push_back(make_object<book>(2, "Carrie", nullobj, 1974));
@@ -79,8 +90,19 @@ TEST_CASE_METHOD(SessionFixture, "Test insert object with has many relation", "[
 
     validate_author_state(s_king, object_state::Transient);
     auto res = ses.insert(s_king);
-  REQUIRE(res.is_ok());
+    REQUIRE(res);
     validate_author_state(s_king, object_state::Persistent);
+
+    auto author_result = ses.find<author>(s_king->id);
+    REQUIRE(author_result);
+    REQUIRE(author_result->is_persistent());
+    REQUIRE(author_result.value()->books.size() == 5);
+  }
+
+  auto author_result = ses.find<author>(1);
+  REQUIRE(author_result);
+  REQUIRE(author_result->is_persistent());
+  REQUIRE(author_result.value()->books.size() == 5);
 }
 
 TEST_CASE_METHOD(SessionFixture, "Test insert object with has many relation with identity", "[session][insert][has_many][identity]") {

test/backends/SessionInsertHasManyToManyTest.cpp

@@ -14,66 +14,6 @@ using namespace matador::object;
 using namespace matador::test;
 using namespace matador::query::meta;
 
-namespace matador::test {
-template<const utils::primary_key_attribute &PkAttribute>
-struct recipe_pk_generator;
-
-template<const utils::primary_key_attribute &PkAttribute>
-struct ingredient_pk_generator {
-  unsigned int id{};
-  std::string name;
-  collection<object_ptr<recipe_pk_generator<PkAttribute>>> recipes{};
-
-  ingredient_pk_generator() = default;
-
-  explicit ingredient_pk_generator(std::string name)
-  : name(std::move(name)) {
-  }
-
-  ingredient_pk_generator(std::string name, std::vector<object_ptr<recipe_pk_generator<PkAttribute>>> recps)
-  : name(std::move(name))
-  , recipes(std::move(recps)){}
-
-  template<class Operator>
-  void process(Operator &op) {
-    namespace field = matador::access;
-    field::primary_key(op, "id", id, PkAttribute);
-    field::attribute(op, "name", name, UniqueVarChar255);
-    field::has_many_to_many(op, "recipe_ingredients", recipes, "ingredient_id", "recipe_id", utils::CascadeAllFetchEager);
-  }
-};
-
-template<const utils::primary_key_attribute &PkAttribute>
-struct recipe_pk_generator {
-  unsigned int id{};
-  std::string name;
-  collection<object_ptr<ingredient_pk_generator<PkAttribute>>> ingredients{};
-
-  recipe_pk_generator() = default;
-  explicit recipe_pk_generator(std::string name)
-  : name(std::move(name)) {
-  }
-  recipe_pk_generator(std::string name, std::vector<object_ptr<ingredient_pk_generator<PkAttribute>>> ings)
-  : name(std::move(name))
-  , ingredients(std::move(ings)){}
-
-  template<class Operator>
-  void process(Operator &op) {
-    namespace field = matador::access;
-    field::primary_key(op, "id", id, PkAttribute);
-    field::attribute(op, "name", name, UniqueVarChar255);
-    field::has_many_to_many(op, "recipe_ingredients", ingredients, utils::CascadeAllFetchLazy);
-  }
-};
-
-using ingredient_identity = ingredient_pk_generator<utils::Identity>;
-using ingredient_table = ingredient_pk_generator<utils::Table>;
-using ingredient_sequence = ingredient_pk_generator<utils::Sequence>;
-using recipe_identity = recipe_pk_generator<utils::Identity>;
-using recipe_table = recipe_pk_generator<utils::Table>;
-using recipe_sequence = recipe_pk_generator<utils::Sequence>;
-}
-
 TEST_CASE_METHOD(SessionFixture, "Test insert object with has many to many relation", "[session][insert][has_many_to_many]") {
   auto result = schema.attach<recipe>("recipes")
     .and_then( [this] { return schema.attach<ingredient>("ingredients"); } )

test/core/CMakeLists.txt

@@ -5,6 +5,7 @@ list(APPEND CMAKE_MODULE_PATH ${catch2_SOURCE_DIR}/extras)
 add_executable(CoreTests
   ../backends/SchemaFixture.hpp
   logger/LoggerTest.cpp
+  object/CollectionTest.cpp
   object/ObjectCacheTest.cpp
   object/ObjectTest.cpp
   object/PrimaryKeyResolverTest.cpp

test/core/object/CollectionTest.cpp

@@ -0,0 +1,16 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include "matador/object/collection.hpp"
+#include "matador/object/object.hpp"
+
+#include <iostream>
+
+using namespace matador::object;
+
+TEST_CASE("Test collection", "[collection]") {
+    collection<int> ints{{1,2,3,4}};
+
+    for (auto const& i : ints) {
+        std::cout << i << std::endl ;
+    }
+}

test/core/object/ObjectCacheTest.cpp

@@ -2,7 +2,9 @@
 
 #include "matador/object/object_cache.hpp"
 #include "matador/object/object_resolver.hpp"
+
 #include "matador/utils/identifier.hpp"
+#include "matador/utils/message_bus.hpp"
 
 #include "../test/models/person.hpp"
 
@@ -57,8 +59,9 @@ private:
 };
 } // namespace
 
-TEST_CASE("object_cache: acquire_proxy returns the same proxy instance across threads", "[object][cache][threadsafe]") {
+TEST_CASE("ObjectCache: acquire_proxy returns the same proxy instance across threads", "[object][cache][threadsafe]") {
-  matador::object::object_cache cache;
+  matador::utils::message_bus bus;
+  matador::object::object_cache cache(bus);
   const matador::utils::identifier id{123};
 
   std::atomic_int calls{0};
@@ -88,8 +91,9 @@ TEST_CASE("object_cache: acquire_proxy returns the same proxy instance across th
   }
 }
 
-TEST_CASE("object_cache: attach_entity makes is_loaded/get_entity reflect presence", "[object][cache]") {
+TEST_CASE("ObjectCache: attach_entity makes is_loaded/get_entity reflect presence", "[object][cache]") {
-  matador::object::object_cache cache;
+  matador::utils::message_bus bus;
+  matador::object::object_cache cache(bus);
   const matador::utils::identifier id{42};
 
   REQUIRE_FALSE(cache.is_loaded<person>(id));
@@ -106,8 +110,9 @@ TEST_CASE("object_cache: attach_entity makes is_loaded/get_entity reflect presen
   REQUIRE(got->name == "hans");
 }
 
-TEST_CASE("object_cache: erase invalidates existing proxies", "[object][cache]") {
+TEST_CASE("ObjectCache: erase invalidates existing proxies", "[object][cache]") {
-  matador::object::object_cache cache;
+  matador::utils::message_bus bus;
+  matador::object::object_cache cache(bus);
   const matador::utils::identifier id{9};
 
   std::atomic_int calls{0};

test/core/object/ObjectTest.cpp

@@ -7,7 +7,7 @@
 #include "../test/models/author.hpp"
 #include "../test/models/book.hpp"
 
-TEST_CASE("Generate object from type", "[object][generate]") {
+TEST_CASE("Object: Generate object from type", "[object][generate]") {
   using namespace matador;
   object::repository repo;
   auto result = repo.attach<test::author>("authors");

test/core/utils/IdentifierTest.cpp

@@ -6,7 +6,7 @@
 
 using namespace matador::utils;
 
-TEST_CASE("Test create identifier", "[identifier][create]") {
+TEST_CASE("Identifier: Test create identifier", "[identifier][create]") {
   const identifier id;
 
   REQUIRE(id.is_null());
@@ -16,7 +16,7 @@ TEST_CASE("Test create identifier", "[identifier][create]") {
   REQUIRE(id.str() == "null");
 }
 
-TEST_CASE("Test assign value to identifier", "[identifier][assign]") {
+TEST_CASE("Identifier: Test assign value to identifier", "[identifier][assign]") {
   identifier id;
 
   REQUIRE(id.is_null());
@@ -48,7 +48,7 @@ TEST_CASE("Test assign value to identifier", "[identifier][assign]") {
   // REQUIRE(id == identifier{"UniqueId"});
 }
 
-TEST_CASE("Test compare identifier", "[identifier][compare]") {
+TEST_CASE("Identifier: Test compare identifier", "[identifier][compare]") {
   identifier id1{6}, id2{7};
 
   REQUIRE(id1 != id2);
@@ -68,7 +68,7 @@ identifier create(const int id) {
   return identifier{id};
 }
 
-TEST_CASE("Test copy identifier" "[identifier][copy]") {
+TEST_CASE("Identifier: Test copy identifier" "[identifier][copy]") {
   identifier id1{"Unique"};
   REQUIRE(id1.is_valid());
   REQUIRE(id1.str() == "Unique");
@@ -92,7 +92,7 @@ TEST_CASE("Test copy identifier" "[identifier][copy]") {
   id3 = id1;
 }
 
-TEST_CASE("Test move identifier", "[identifier][move]") {
+TEST_CASE("Identifier: Test move identifier", "[identifier][move]") {
   identifier id1{6};
 
   REQUIRE(id1.is_integer());
@@ -103,7 +103,7 @@ TEST_CASE("Test move identifier", "[identifier][move]") {
   REQUIRE(id2.is_integer());
 }
 
-TEST_CASE("identifier assignment from integer types", "[utils][identifier][assign]") {
+TEST_CASE("Identifier: Identifier assignment from integer types", "[utils][identifier][assign]") {
   identifier id;
 
   id = int8_t{-5};
@@ -125,7 +125,7 @@ TEST_CASE("identifier assignment from integer types", "[utils][identifier][assig
   REQUIRE(id.is_valid());
 }
 
-TEST_CASE("identifier assignment from string type", "[utils][identifier][assign]") {
+TEST_CASE("Identifier: Identifier assignment from string type", "[utils][identifier][assign]") {
   identifier id;
 
   id = std::string{"hello"};
@@ -140,7 +140,7 @@ TEST_CASE("identifier assignment from string type", "[utils][identifier][assign]
   REQUIRE_FALSE(id.is_valid());
 }
 
-TEST_CASE("identifier assignment from const char*", "[utils][identifier][assign]") {
+TEST_CASE("Identifier: Identifier assignment from const char*", "[utils][identifier][assign]") {
   identifier id;
 
   id = "world";
@@ -155,7 +155,7 @@ TEST_CASE("identifier assignment from const char*", "[utils][identifier][assign]
   REQUIRE_FALSE(id.is_valid());
 }
 
-TEST_CASE("identifier assignment from nullptr", "[utils][identifier][assign]") {
+TEST_CASE("Identifier: Identifier assignment from nullptr", "[utils][identifier][assign]") {
   identifier id{42};
 
   REQUIRE(id.is_valid());
@@ -168,7 +168,7 @@ TEST_CASE("identifier assignment from nullptr", "[utils][identifier][assign]") {
   REQUIRE_FALSE(id.is_valid());
 }
 
-TEST_CASE("identifier reassignment between types", "[utils][identifier][assign]") {
+TEST_CASE("Identifier: Identifier reassignment between types", "[utils][identifier][assign]") {
   identifier id{uint64_t{7}};
 
   REQUIRE(id.is_integer());
@@ -189,7 +189,7 @@ TEST_CASE("identifier reassignment between types", "[utils][identifier][assign]"
   REQUIRE(id.str() == "null");
 }
 
-TEST_CASE("identifier as() returns exact integer type", "[utils][identifier][as]") {
+TEST_CASE("Identifier: Identifier as() returns exact integer type", "[utils][identifier][as]") {
   identifier id{int32_t{42}};
 
   const auto as_i32 = id.as<int32_t>();
@@ -200,7 +200,7 @@ TEST_CASE("identifier as() returns exact integer type", "[utils][identifier][as]
   REQUIRE(as_i64.is_error());
 }
 
-TEST_CASE("identifier as() returns exact string type", "[utils][identifier][as]") {
+TEST_CASE("Identifier: Identifier as() returns exact string type", "[utils][identifier][as]") {
   identifier id{std::string{"hello"}};
 
   const auto as_string = id.as<std::string>();
@@ -211,7 +211,7 @@ TEST_CASE("identifier as() returns exact string type", "[utils][identifier][as]"
   REQUIRE(as_i32.is_error());
 }
 
-TEST_CASE("identifier as() returns null type failure for null identifier", "[utils][identifier][as]") {
+TEST_CASE("Identifier: Identifier as() returns null type failure for null identifier", "[utils][identifier][as]") {
   identifier id{nullptr};
 
   const auto as_i32 = id.as<int32_t>();
@@ -221,7 +221,7 @@ TEST_CASE("identifier as() returns null type failure for null identifier", "[uti
   REQUIRE(as_string.is_error());
 }
 
-TEST_CASE("identifier convert() converts between integer types", "[utils][identifier][convert]") {
+TEST_CASE("Identifier: Identifier convert() converts between integer types", "[utils][identifier][convert]") {
   identifier id{int32_t{123}};
 
   const auto as_i64 = id.convert<int64_t>();
@@ -233,21 +233,21 @@ TEST_CASE("identifier convert() converts between integer types", "[utils][identi
   REQUIRE(*as_u8 == 123);
 }
 
-TEST_CASE("identifier convert() rejects out of range integer conversion", "[utils][identifier][convert]") {
+TEST_CASE("Identifier: Identifier convert() rejects out of range integer conversion", "[utils][identifier][convert]") {
   identifier id{int32_t{300}};
 
   const auto as_u8 = id.convert<uint8_t>();
   REQUIRE(as_u8.is_error());
 }
 
-TEST_CASE("identifier convert() rejects negative to unsigned conversion", "[utils][identifier][convert]") {
+TEST_CASE("Identifier: Identifier convert() rejects negative to unsigned conversion", "[utils][identifier][convert]") {
   identifier id{int32_t{-1}};
 
   const auto as_u32 = id.convert<uint32_t>();
   REQUIRE(as_u32.is_error());
 }
 
-TEST_CASE("identifier convert() rejects non-integer source types", "[utils][identifier][convert]") {
+TEST_CASE("Identifier: Identifier convert() rejects non-integer source types", "[utils][identifier][convert]") {
   identifier id{std::string{"123"}};
 
   const auto as_i32 = id.convert<int32_t>();
@@ -258,7 +258,7 @@ TEST_CASE("identifier convert() rejects non-integer source types", "[utils][iden
   REQUIRE(null_to_i64.is_error());
 }
 
-TEST_CASE("identifier convert() works with unsigned integer sources", "[utils][identifier][convert]") {
+TEST_CASE("Identifier: Identifier convert() works with unsigned integer sources", "[utils][identifier][convert]") {
   identifier id{uint16_t{500}};
 
   const auto as_i32 = id.convert<int32_t>();
@@ -269,7 +269,7 @@ TEST_CASE("identifier convert() works with unsigned integer sources", "[utils][i
   REQUIRE(as_u8.is_error());
 }
 
-TEST_CASE("identifier as() and convert() behave consistently for same integer type", "[utils][identifier][as][convert]") {
+TEST_CASE("Identifier: Identifier as() and convert() behave consistently", "[utils][identifier][as][convert]") {
   identifier id{uint64_t{77}};
 
   const auto as_u64 = id.as<uint64_t>();
@@ -281,7 +281,7 @@ TEST_CASE("identifier as() and convert() behave consistently for same integer ty
   REQUIRE(*conv_u64 == 77);
 }
 
-TEST_CASE("identifier assign from value", "[utils][identifier][assign]") {
+TEST_CASE("Identifier: Identifier assign from value", "[utils][identifier][assign]") {
   identifier id;
 
   value v1{int32_t{17}};
@@ -301,7 +301,7 @@ TEST_CASE("identifier assign from value", "[utils][identifier][assign]") {
   REQUIRE(r3.is_error());
 }
 
-TEST_CASE("identifier assign from value with exact type mapping", "[utils][identifier][assign]") {
+TEST_CASE("Identifier: Identifier assign from value with exact type mapping", "[utils][identifier][assign]") {
   identifier id;
 
   SECTION("integer types") {
@@ -328,7 +328,7 @@ TEST_CASE("identifier assign from value with exact type mapping", "[utils][ident
   }
 }
 
-TEST_CASE("identifier::to_database_type converts internal value to database_type", "[identifier]") {
+TEST_CASE("Identifier: Identifier::to_database_type converts internal value", "[identifier][to_database_type]") {
   SECTION("null identifier becomes nullptr") {
     identifier id{nullptr};
 
@@ -337,7 +337,7 @@ TEST_CASE("identifier::to_database_type converts internal value to database_type
     REQUIRE(std::holds_alternative<std::nullptr_t>(db_value));
   }
 
-  SECTION("signed integral identifier becomes same signed database type") {
+  SECTION("Identifier: Signed integral identifier becomes same signed database type") {
     identifier id{int32_t{42}};
 
     const auto db_value = id.to_database_type();
@@ -346,7 +346,7 @@ TEST_CASE("identifier::to_database_type converts internal value to database_type
     REQUIRE(std::get<int32_t>(db_value) == 42);
   }
 
-  SECTION("unsigned integral identifier becomes same unsigned database type") {
+  SECTION("Identifier: Unsigned integral identifier becomes same unsigned database type") {
     identifier id{uint64_t{123456789ULL}};
 
     const auto db_value = id.to_database_type();
@@ -355,7 +355,7 @@ TEST_CASE("identifier::to_database_type converts internal value to database_type
     REQUIRE(std::get<uint64_t>(db_value) == 123456789ULL);
   }
 
-  SECTION("string identifier becomes std::string database type") {
+  SECTION("Identifier: String identifier becomes std::string database type") {
     identifier id{std::string{"customer_1"}};
 
     const auto db_value = id.to_database_type();

test/core/utils/MessageBusTest.cpp

@@ -18,7 +18,7 @@ public:
 
 using namespace matador::utils;
 
-TEST_CASE("Basic publish/subscribe works", "[MessageBus]") {
+TEST_CASE("MessageBus: Basic publish/subscribe works", "[MessageBus]") {
     message_bus bus;
     int counter = 0;
 
@@ -32,7 +32,7 @@ TEST_CASE("Basic publish/subscribe works", "[MessageBus]") {
     REQUIRE(counter == 3);
 }
 
-TEST_CASE("Filtering works", "[MessageBus]") {
+TEST_CASE("MessageBus: Filtering works", "[MessageBus]") {
     message_bus bus;
     int counter = 0;
 
@@ -49,7 +49,7 @@ TEST_CASE("Filtering works", "[MessageBus]") {
     REQUIRE(counter == 6); // only 2 + 4
 }
 
-TEST_CASE("Member function subscription works", "[MessageBus]") {
+TEST_CASE("MessageBus: Member function subscription works", "[MessageBus]") {
     message_bus bus;
     Receiver r;
 
@@ -62,7 +62,7 @@ TEST_CASE("Member function subscription works", "[MessageBus]") {
     REQUIRE(r.received[1] == "world");
 }
 
-TEST_CASE("Shared_ptr instance subscription works", "[MessageBus]") {
+TEST_CASE("MessageBus: SharedPtr instance subscription works", "[MessageBus]") {
     message_bus bus;
     const auto r = std::make_shared<Receiver>();
 
@@ -73,7 +73,7 @@ TEST_CASE("Shared_ptr instance subscription works", "[MessageBus]") {
     REQUIRE(r->received[0] == "foo");
 }
 
-TEST_CASE("RAII unsubscription works", "[MessageBus]") {
+TEST_CASE("MessageBus: RAII unsubscription works", "[MessageBus]") {
     message_bus bus;
     int counter = 0;
 
@@ -90,7 +90,7 @@ TEST_CASE("RAII unsubscription works", "[MessageBus]") {
     REQUIRE(counter == 5);
 }
 
-TEST_CASE("Type-erased AnyMessage publish works", "[MessageBus]") {
+TEST_CASE("MessageBus: Type-erased AnyMessage publish works", "[MessageBus]") {
     message_bus bus;
     int counter = 0;
 
@@ -104,7 +104,7 @@ TEST_CASE("Type-erased AnyMessage publish works", "[MessageBus]") {
     REQUIRE(counter == 10);
 }
 
-TEST_CASE("Multiple subscribers all receive messages", "[MessageBus]") {
+TEST_CASE("MessageBus: Multiple subscribers all receive messages", "[MessageBus]") {
     message_bus bus;
     int a = 0, b = 0;
 
@@ -116,7 +116,7 @@ TEST_CASE("Multiple subscribers all receive messages", "[MessageBus]") {
     REQUIRE(b == 3);
 }
 
-TEST_CASE("Stress test with multi-threaded publish and subscribe", "[MessageBus][stress]") {
+TEST_CASE("MessageBus: Stress test with multi-threaded publish and subscribe", "[MessageBus][stress]") {
     message_bus bus;
     std::atomic<int> counter{0};
     constexpr int numThreads = 8;

test/core/utils/ResultTest.cpp

@@ -5,13 +5,15 @@
 #include "matador/utils/result.hpp"
 
 namespace matador::test {
+namespace {
 enum class math_error : int32_t {
   OK = 0,
   DIVISION_BY_ZERO = 1,
   FAILURE = 2
 };
+}
 
-utils::result<float, math_error>divide(const float x, const float y) {
+static utils::result<float, math_error>divide(const float x, const float y) {
   if (y == 0) {
     return utils::failure(math_error::DIVISION_BY_ZERO);
   }
@@ -19,15 +21,15 @@ utils::result<float, math_error>divide(const float x, const float y) {
   return utils::ok(x / y);
 }
 
-utils::result<float, math_error>multiply(const float x, const float y) {
+static utils::result<float, math_error>multiply(const float x, const float y) {
   return utils::ok(x * y);
 }
 
-utils::result<float, math_error>plus(const float x, const float y) {
+static utils::result<float, math_error>plus(const float x, const float y) {
   return utils::ok(x + y);
 }
 
-utils::result<void, math_error>action_on_greater_42(const float i) {
+static utils::result<void, math_error>action_on_greater_42(const float i) {
   if (i > 42) {
     return utils::ok<void>();
   }
@@ -88,7 +90,7 @@ TEST_CASE("Test result", "[result]") {
   REQUIRE(!res2.is_ok());
   REQUIRE(res2.is_error());
   const auto e = res2.err();
-//  REQUIRE(res2.err() == "division by zero error");
+  REQUIRE(res2.err() == "division by zero error");
 
   res = test::divide(4, 2)
     .and_then([](const auto &val) { return test::multiply(val, 5); })

test/core/utils/ThreadPoolTest.cpp

@@ -4,21 +4,21 @@
 
 using namespace matador::utils;
 
-TEST_CASE("thread_pool creates and rejects zero-sized construction") {
+TEST_CASE("ThreadPool: thread_pool creates and rejects zero-sized construction") {
     REQUIRE_THROWS(thread_pool(0));
 
     const thread_pool tp(2);
     REQUIRE(tp.size() == 2);
 }
 
-TEST_CASE("thread_pool schedules and runs simple tasks") {
+TEST_CASE("ThreadPool: thread_pool schedules and runs simple tasks") {
     thread_pool pool(3);
     auto fut = pool.schedule([](cancel_token&, const int x) { return x * 10; }, 7);
     REQUIRE(fut);
     REQUIRE(fut.value().get() == 70);
 }
 
-TEST_CASE("thread_pool parallel computation and results") {
+TEST_CASE("ThreadPool: thread_pool parallel computation and results") {
     thread_pool pool(4);
     std::vector<std::future<int>> futs;
     for (int i = 1; i <= 20; ++i) {
@@ -33,7 +33,7 @@ TEST_CASE("thread_pool parallel computation and results") {
     REQUIRE(sum == 230); // (2+3+...+21) = (21*22/2)-(1) = 231-1
 }
 
-TEST_CASE("thread_pool rejects scheduling after shutdown") {
+TEST_CASE("ThreadPool: thread_pool rejects scheduling after shutdown") {
     thread_pool pool(2);
     pool.shutdown();
     auto result = pool.schedule([](cancel_token&) { return 1; });
@@ -41,7 +41,7 @@ TEST_CASE("thread_pool rejects scheduling after shutdown") {
     REQUIRE(result.err().find("shut down") != std::string::npos);
 }
 
-TEST_CASE("thread_pool supports cancel_token for not-yet-run task") {
+TEST_CASE("ThreadPool: thread_pool supports cancel_token for not-yet-run task") {
     thread_pool pool(1);
     std::atomic ran{false};
 
@@ -73,7 +73,7 @@ TEST_CASE("thread_pool supports cancel_token for not-yet-run task") {
     // If started before cancel, may be 100 (rare but possible)
 }
 
-TEST_CASE("thread_pool: shutdown finishes all running tasks") {
+TEST_CASE("ThreadPool: thread_pool: shutdown finishes all running tasks") {
     thread_pool pool(2);
     std::atomic counter{0};
     std::vector<std::future<void>> futs;

test/core/utils/VersionTest.cpp

@@ -4,7 +4,26 @@
 
 using namespace matador::utils;
 
-TEST_CASE("Test version interface", "[version][interface]") {
+TEST_CASE("Version: Test form string", "[version][from_string]") {
+  REQUIRE(version::from_string("1.2.3").is_ok());
+  REQUIRE(version::from_string("0.0.0").is_ok());
+
+  REQUIRE(version::from_string("1.2").is_error());
+  REQUIRE(version::from_string("1.2.3.4").is_error());
+  REQUIRE(version::from_string("1.2.3abc").is_error());
+  REQUIRE(version::from_string("abc").is_error());
+  REQUIRE(version::from_string("-1.2.3").is_error());
+}
+
+TEST_CASE("Version: Test comparison", "[version][comparison]") {
+  REQUIRE(version(1, 2, 3) == version(1, 2, 3));
+  REQUIRE(version(1, 2, 3) < version(1, 2, 4));
+  REQUIRE(version(1, 2, 3) < version(1, 3, 0));
+  REQUIRE(version(1, 2, 3) < version(2, 0, 0));
+  REQUIRE(version(2, 0, 0) > version(1, 9, 9));
+}
+
+TEST_CASE("Version: Test interface", "[version][interface]") {
   version v0;
 
   REQUIRE(v0.major() == 0);
@@ -38,8 +57,8 @@ TEST_CASE("Test version interface", "[version][interface]") {
   REQUIRE(v2 == v1);
 }
 
-TEST_CASE("Test version parsing", "[version][parse]") {
+TEST_CASE("Version: Test parsing", "[version][parse]") {
-  const auto version_str{"13.67.34"};
+  constexpr auto version_str{"13.67.34"};
   const auto v1 = version::from_string(version_str);
   REQUIRE(v1.is_ok());
 

test/models/recipe.hpp

@@ -57,6 +57,64 @@ struct recipe {
     field::has_many_to_many(op, "recipe_ingredients", ingredients, utils::CascadeAllFetchLazy);
   }
 };
+
+template<const utils::primary_key_attribute &PkAttribute>
+struct recipe_pk_generator;
+
+template<const utils::primary_key_attribute &PkAttribute>
+struct ingredient_pk_generator {
+  unsigned int id{};
+  std::string name;
+  object::collection<object::object_ptr<recipe_pk_generator<PkAttribute>>> recipes{};
+
+  ingredient_pk_generator() = default;
+
+  explicit ingredient_pk_generator(std::string name)
+  : name(std::move(name)) {
+  }
+
+  ingredient_pk_generator(std::string name, std::vector<object::object_ptr<recipe_pk_generator<PkAttribute>>> recps)
+  : name(std::move(name))
+  , recipes(std::move(recps)){}
+
+  template<class Operator>
+  void process(Operator &op) {
+    namespace field = matador::access;
+    field::primary_key(op, "id", id, PkAttribute);
+    field::attribute(op, "name", name, UniqueVarChar255);
+    field::has_many_to_many(op, "recipe_ingredients", recipes, "ingredient_id", "recipe_id", utils::CascadeAllFetchEager);
+  }
+};
+
+template<const utils::primary_key_attribute &PkAttribute>
+struct recipe_pk_generator {
+  unsigned int id{};
+  std::string name;
+  object::collection<object::object_ptr<ingredient_pk_generator<PkAttribute>>> ingredients{};
+
+  recipe_pk_generator() = default;
+  explicit recipe_pk_generator(std::string name)
+  : name(std::move(name)) {
+  }
+  recipe_pk_generator(std::string name, std::vector<object::object_ptr<ingredient_pk_generator<PkAttribute>>> ings)
+  : name(std::move(name))
+  , ingredients(std::move(ings)){}
+
+  template<class Operator>
+  void process(Operator &op) {
+    namespace field = matador::access;
+    field::primary_key(op, "id", id, PkAttribute);
+    field::attribute(op, "name", name, UniqueVarChar255);
+    field::has_many_to_many(op, "recipe_ingredients", ingredients, utils::CascadeAllFetchLazy);
+  }
+};
+
+using ingredient_identity = ingredient_pk_generator<utils::Identity>;
+using ingredient_table = ingredient_pk_generator<utils::Table>;
+using ingredient_sequence = ingredient_pk_generator<utils::Sequence>;
+using recipe_identity = recipe_pk_generator<utils::Identity>;
+using recipe_table = recipe_pk_generator<utils::Table>;
+using recipe_sequence = recipe_pk_generator<utils::Sequence>;
 }
 
 #endif //QUERY_RECIPE_HPP

test/orm/CMakeLists.txt

@@ -3,6 +3,8 @@ CPMAddPackage("gh:catchorg/Catch2@3.14.0")
 list(APPEND CMAKE_MODULE_PATH ${catch2_SOURCE_DIR}/extras)
 
 add_executable(OrmTests
+  ../utils/RecordingObserver.cpp
+  ../utils/RecordingObserver.hpp
   backend/test_backend_service.cpp
   backend/test_backend_service.hpp
   backend/test_connection.cpp
@@ -16,6 +18,7 @@ add_executable(OrmTests
   query/ColumnExpressionTest.cpp
   query/ColumnGeneratorTest.cpp
   query/CriteriaTests.cpp
+  query/DeleteQueryBuilderTest.cpp
   query/GeneratorTests.cpp
   query/InsertQueryBuilderTest.cpp
   query/QueryBuilderTest.cpp
@@ -32,8 +35,6 @@ add_executable(OrmTests
   sql/StatementCacheTest.cpp
   utils/auto_reset_event.cpp
   utils/auto_reset_event.hpp
-  ../utils/RecordingObserver.hpp
-  ../utils/RecordingObserver.cpp
 )
 
 target_link_libraries(OrmTests matador-orm matador-core Catch2::Catch2WithMain)

test/orm/query/DeleteQueryBuilderTest.cpp

@@ -0,0 +1,108 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include "matador/object/object_ptr.hpp"
+
+#include "matador/sql/backend_provider.hpp"
+#include "matador/sql/connection.hpp"
+#include "matador/sql/interface/connection_impl.hpp"
+
+#include "matador/query/schema.hpp"
+
+#include "matador/query/delete_query_builder.hpp"
+
+#include "QueryFixture.hpp"
+
+#include "../../models/author.hpp"
+#include "../../models/book.hpp"
+#include "../../models/airplane.hpp"
+#include "../../models/flight.hpp"
+#include "../../models/recipe.hpp"
+
+using namespace matador::object;
+using namespace matador::sql;
+using namespace matador::query;
+using namespace matador::utils;
+using namespace matador::test;
+
+TEST_CASE_METHOD(QueryFixture, "delete query builder test", "[query][delete_query_builder]") {
+  schema scm;
+  auto result = scm.attach<airplane>("airplanes")
+    .and_then( [&scm] { return scm.attach<flight>("flights"); } );
+  REQUIRE(result);
+
+  const auto contexts_by_type = to_contexts_by_name(scm, db->dialect());
+  delete_query_builder<airplane> dqb(scm, contexts_by_type);
+
+  const auto a380 = make_object<airplane>(1, "Boeing", "A380"  );
+  auto build_result = dqb.build(a380);
+  REQUIRE(build_result.is_ok());
+
+  const auto& stmts = *build_result;
+  REQUIRE(stmts.size() == 1);
+}
+
+TEST_CASE_METHOD(QueryFixture, "Test delete builder has many", "[query][delete_query_builder][has_many]") {
+  schema scm;
+  const auto result = scm.attach<book>("books")
+    .and_then( [&scm] { return scm.attach<author>("authors"); } );
+  REQUIRE(result.is_ok());
+
+  auto s_king = make_object<author>(1, "Steven", "King", "21.9.1947", 1956, false);
+
+  s_king->books.push_back(make_object<book>(2, "Carrie", object_ptr<author>{}, 1974));
+  s_king->books.push_back(make_object<book>(3, "The Shining", object_ptr<author>{}, 1977));
+  s_king->books.push_back(make_object<book>(4, "It", object_ptr<author>{}, 1986));
+  s_king->books.push_back(make_object<book>(5, "Misery", object_ptr<author>{}, 1987));
+  s_king->books.push_back(make_object<book>(6, "The Dark Tower: The Gunslinger", object_ptr<author>{}, 1982));
+
+  const auto contexts_by_type = to_contexts_by_name(scm, db->dialect());
+  delete_query_builder<author> dqb(scm, contexts_by_type);
+
+  auto build_result = dqb.build(s_king);
+  REQUIRE(build_result.is_ok());
+
+  const auto& stmts = *build_result;
+  REQUIRE_FALSE(stmts.empty());
+  REQUIRE(stmts.size() == 6);
+}
+
+TEST_CASE_METHOD(QueryFixture, "Test delete builder has many to many", "[query][delete_query_builder][many_to_many]") {
+  schema scm;
+  const auto result = scm.attach<recipe>("recipes")
+    .and_then( [&scm] { return scm.attach<ingredient>("ingredients"); } );
+  REQUIRE(result.is_ok());
+
+  std::vector ingredients {
+    make_object<ingredient>(1, "Apple"),
+    make_object<ingredient>(2, "Strawberry"),
+    make_object<ingredient>(3, "Pineapple"),
+    make_object<ingredient>(4, "Sugar"),
+    make_object<ingredient>(5, "Flour"),
+    make_object<ingredient>(6, "Butter"),
+    make_object<ingredient>(7, "Beans")
+  };
+
+  for (auto &i : ingredients) {
+    i.change_state(object_state::Persistent);
+  }
+
+  std::vector recipes {
+    make_object<recipe>(1, "Apple Pie", std::vector{ingredients[0], ingredients[3], ingredients[4]}),
+    make_object<recipe>(2, "Strawberry Cake", std::vector{ingredients[5], ingredients[6]}),
+    make_object<recipe>(3, "Pineapple Pie", std::vector{ingredients[0], ingredients[1], ingredients[2]})
+  };
+
+  for (auto &r : recipes) {
+    r.change_state(object_state::Persistent);
+  }
+
+  const auto contexts_by_type = to_contexts_by_name(scm, db->dialect());
+  delete_query_builder<recipe> dqb(scm, contexts_by_type);
+
+  auto build_result = dqb.build(recipes[0]);
+  REQUIRE(build_result.is_ok());
+
+  const auto& stmts = *build_result;
+  REQUIRE_FALSE(stmts.empty());
+  REQUIRE(stmts.size() == 7);
+}

test/orm/query/InsertQueryBuilderTest.cpp

@@ -6,13 +6,11 @@
 #include "matador/sql/connection.hpp"
 #include "matador/sql/interface/connection_impl.hpp"
 
-#include "matador/query/query_contexts.hpp"
-#include "matador/query/query.hpp"
 #include "matador/query/schema.hpp"
 
 #include "matador/query/insert_query_builder.hpp"
 
-#include "../backend/test_backend_service.hpp"
+#include "QueryFixture.hpp"
 
 #include "../../models/author.hpp"
 #include "../../models/book.hpp"
@@ -24,58 +22,15 @@ using namespace matador::object;
 using namespace matador::sql;
 using namespace matador::query;
 using namespace matador::utils;
-
-std::unordered_map<std::type_index, query_contexts> to_contexts_by_name(const schema& scm, const dialect& d) {
-  std::unordered_map<std::type_index, query_contexts> contexts_by_type;
-  for (const auto &[type, node] : scm) {
-    query_contexts queries;
-
-    // SELECT all
-    queries.select_all = select(node.table())
-      .from(node.name())
-      .compile(d);
-    if (node.table().has_primary_key()) {
-      // SELECT one
-      queries.select_one = select(node.table())
-        .from(node.name())
-        .where(*node.table().primary_key_column() == _)
-        .compile(d);
-      // UPDATE one
-      auto update_set = update(node.table());
-      for (const auto &col: node.table().columns()) {
-        update_set.set(col, _);
-      }
-      queries.update_one = update_set.where(*node.table().primary_key_column() == _)
-        .compile(d);
-      // DELETE one
-      queries.delete_one = remove()
-        .from(node.name())
-        .where(*node.table().primary_key_column() == _)
-        .compile(d);
-    }
-    // INSERT one
-    queries.insert = insert()
-      .into(node.name(), node.table())
-      .values(generator::placeholders(node.table().columns().size()))
-      .compile(d);
-
-    contexts_by_type[node.node().type_index()] = queries;
-  }
-  
-  return contexts_by_type;
-}
-
-TEST_CASE("insert query builder test", "[query][insert_query_builder]") {
 using namespace matador::test;
-  backend_provider::instance().register_backend("noop", std::make_unique<orm::test_backend_service>());
-  connection db("noop://noop.db");
 
+TEST_CASE_METHOD(QueryFixture, "insert query builder test", "[query][insert_query_builder]") {
   schema scm;
   auto result = scm.attach<airplane>("airplanes")
     .and_then( [&scm] { return scm.attach<flight>("flights"); } );
   REQUIRE(result);
 
-  const auto contexts_by_type = to_contexts_by_name(scm, db.dialect());
+  const auto contexts_by_type = to_contexts_by_name(scm, db->dialect());
   insert_query_builder<airplane> iqb(scm, contexts_by_type);
 
   const auto a380 = make_object<airplane>(1, "Boeing", "A380"  );
@@ -86,11 +41,7 @@ TEST_CASE("insert query builder test", "[query][insert_query_builder]") {
   REQUIRE(stmts.size() == 1);
 }
 
-TEST_CASE("Test insert builder has many", "[query][insert_query_builder][has_many]") {
+TEST_CASE_METHOD(QueryFixture, "Test insert builder has many", "[query][insert_query_builder][has_many]") {
-  using namespace matador::test;
-  backend_provider::instance().register_backend("noop", std::make_unique<orm::test_backend_service>());
-  connection db("noop://noop.db");
-
   schema scm;
   const auto result = scm.attach<book>("books")
     .and_then( [&scm] { return scm.attach<author>("authors"); } );
@@ -104,7 +55,7 @@ TEST_CASE("Test insert builder has many", "[query][insert_query_builder][has_man
   s_king->books.push_back(make_object<book>(5, "Misery", object_ptr<author>{}, 1987));
   s_king->books.push_back(make_object<book>(6, "The Dark Tower: The Gunslinger", object_ptr<author>{}, 1982));
 
-  const auto contexts_by_type = to_contexts_by_name(scm, db.dialect());
+  const auto contexts_by_type = to_contexts_by_name(scm, db->dialect());
   insert_query_builder<author> iqb(scm, contexts_by_type);
 
   auto build_result = iqb.build(s_king);
@@ -115,11 +66,7 @@ TEST_CASE("Test insert builder has many", "[query][insert_query_builder][has_man
   REQUIRE(stmts.size() == 6);
 }
 
-TEST_CASE("Test insert builder has many to many", "[query][insert_query_builder][many_to_many]") {
+TEST_CASE_METHOD(QueryFixture, "Test insert builder has many to many", "[query][insert_query_builder][many_to_many]") {
-  using namespace matador::test;
-  backend_provider::instance().register_backend("noop", std::make_unique<orm::test_backend_service>());
-  connection db("noop://noop.db");
-
   schema scm;
   const auto result = scm.attach<recipe>("recipes")
     .and_then( [&scm] { return scm.attach<ingredient>("ingredients"); } );
@@ -141,7 +88,7 @@ TEST_CASE("Test insert builder has many to many", "[query][insert_query_builder]
     make_object<recipe>(3, "Pineapple Pie", std::vector{ingredients[0], ingredients[1], ingredients[2]})
   };
 
-  const auto contexts_by_type = to_contexts_by_name(scm, db.dialect());
+  const auto contexts_by_type = to_contexts_by_name(scm, db->dialect());
   insert_query_builder<recipe> iqb(scm, contexts_by_type);
 
   auto build_result = iqb.build(recipes[0]);

test/orm/query/QueryBuilderTest.cpp

@@ -24,13 +24,13 @@ TEST_CASE_METHOD(QueryFixture, "Test alter table sql statement", "[query][alter]
     .add_constraint("FK_employees_dep_id")
     .foreign_key("dep_id"_col)
     .references("departments", {"id"_col})
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(ALTER TABLE "employees" ADD CONSTRAINT FK_employees_dep_id FOREIGN KEY ("dep_id") REFERENCES departments ("id"))");
   result = alter()
     .table("employees")
     .drop_constraint("FK_employees_dep_id")
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(ALTER TABLE "employees" DROP CONSTRAINT FK_employees_dep_id)");
 }
@@ -46,7 +46,7 @@ TEST_CASE_METHOD(QueryFixture, "Test create table sql statement string", "[query
     .constraints({
         constraint("PK_person").primary_key({"id"})
     })
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"##(CREATE TABLE "person" ("id" BIGINT NOT NULL, "name" VARCHAR(255) NOT NULL, "age" INTEGER NOT NULL, CONSTRAINT PK_person PRIMARY KEY (id)))##");
 
@@ -57,7 +57,7 @@ TEST_CASE_METHOD(QueryFixture, "Test create table sql statement string", "[query
         column("name", basic_type::Varchar, 255),
         column("age", basic_type::UInt16)
     })
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"##(CREATE TABLE "person" ("id" BIGINT NOT NULL AUTO INCREMENT PRIMARY KEY, "name" VARCHAR(255) NOT NULL, "age" INTEGER NOT NULL))##");
 
@@ -81,7 +81,7 @@ TEST_CASE_METHOD(QueryFixture, "Test create table sql statement string", "[query
 TEST_CASE_METHOD(QueryFixture, "Test drop table sql statement string", "[query]") {
   const auto result = drop()
     .table("person")
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(DROP TABLE "person")");
 }
@@ -89,7 +89,7 @@ TEST_CASE_METHOD(QueryFixture, "Test drop table sql statement string", "[query]"
 TEST_CASE_METHOD(QueryFixture, "Test select all columns with asterisk", "[query][select][asterisk]") {
   const auto result = select()
     .from("person")
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT * FROM "person")");
 }
@@ -97,7 +97,7 @@ TEST_CASE_METHOD(QueryFixture, "Test select all columns with asterisk", "[query]
 TEST_CASE_METHOD(QueryFixture, "Test select sql statement string", "[query]") {
   const auto result = select({"id", "name", "age"})
     .from("person")
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT "id", "name", "age" FROM "person")");
 }
@@ -108,7 +108,7 @@ TEST_CASE_METHOD(QueryFixture, "Test insert sql statement string", "[query]") {
     "id", "name", "age"
     })
     .values({7U, "george", 65U})
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(INSERT INTO "person" ("id", "name", "age") VALUES (7, 'george', 65))");
 }
@@ -118,7 +118,7 @@ TEST_CASE_METHOD(QueryFixture, "Test update sql statement string", "[query]") {
     .set("id", 7U)
     .set("name", "george")
     .set("age", 65U)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(UPDATE "person" SET "id"=7, "name"='george', "age"=65)");
 
@@ -130,7 +130,7 @@ TEST_CASE_METHOD(QueryFixture, "Test update sql statement string", "[query]") {
     .order_by("id").asc()
     .limit(3)
     .offset(2)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(UPDATE "person" SET "id"=7, "name"='george', "age"=65 WHERE "id" > 9 ORDER BY "id" ASC LIMIT 3 OFFSET 2)");
 }
@@ -142,7 +142,7 @@ TEST_CASE_METHOD(QueryFixture, "Test update returning statement", "[query][updat
     .set("age", 65U)
     .where("name"_col == "george")
       .returning("id"_col, "name"_col, "age"_col)
-      .str(*db);
+      .str(db->dialect());
 
     REQUIRE(result == R"(UPDATE "person" SET "id"=7, "name"='george', "age"=65 WHERE "name" = 'george' RETURNING "id", "name", "age")");
 }
@@ -155,13 +155,13 @@ TEST_CASE_METHOD(QueryFixture, "Test update limit sql statement", "[query][updat
     .where("name"_col == "george")
     .order_by("id"_col).asc()
     .limit(2)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(UPDATE "person" SET "id"=7, "name"='george', "age"=65 WHERE "name" = 'george' ORDER BY "id" ASC LIMIT 2)");
 }
 
 TEST_CASE_METHOD(QueryFixture, "Test delete sql statement string", "[query]") {
-  const auto result = remove().from("person").str(*db);
+  const auto result = remove().from("person").str(db->dialect());
 
   REQUIRE(result == R"(DELETE FROM "person")");
 }
@@ -172,7 +172,7 @@ TEST_CASE_METHOD(QueryFixture, "Test delete limit sql statement", "[query][delet
     .where("name"_col == "george")
     .order_by("id"_col).asc()
     .limit(2)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(DELETE FROM "person" WHERE "name" = 'george' ORDER BY "id" ASC LIMIT 2)");
 }
@@ -181,14 +181,14 @@ TEST_CASE_METHOD(QueryFixture, "Test select sql statement string with where clau
   auto result = select({"id", "name", "age"})
     .from("person")
     .where("id"_col == 8 && "age"_col > 50)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT "id", "name", "age" FROM "person" WHERE ("id" = 8 AND "age" > 50))");
 
   result = select({"id", "name", "age"})
     .from("person")
     .where("id"_col == _ && "age"_col > 50)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT "id", "name", "age" FROM "person" WHERE ("id" = ? AND "age" > 50))");
 }
@@ -197,14 +197,14 @@ TEST_CASE_METHOD(QueryFixture, "Test insert sql statement with placeholder", "[q
   auto result = insert()
     .into("person", {"id", "name", "age"})
     .values({_, _, _})
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(INSERT INTO "person" ("id", "name", "age") VALUES (?, ?, ?))");
 
   result = insert()
     .into("person", {"id", "name", "age"})
     .values({9, "george", _})
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(INSERT INTO "person" ("id", "name", "age") VALUES (9, 'george', ?))");
 }
@@ -214,7 +214,7 @@ TEST_CASE_METHOD(QueryFixture, "Test insert sql statement with returning", "[que
     .into("person", {"id", "name", "age"})
     .values({9, "george", _})
     .returning("id"_col, "name"_col, "age"_col)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(INSERT INTO "person" ("id", "name", "age") VALUES (9, 'george', ?) RETURNING "id", "name", "age")");
 }
@@ -223,7 +223,7 @@ TEST_CASE_METHOD(QueryFixture, "Test select sql statement string with order by",
   const auto result = select({"id", "name", "age"})
     .from("person")
     .order_by("name"_col).asc()
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT "id", "name", "age" FROM "person" ORDER BY "name" ASC)");
 }
@@ -232,7 +232,7 @@ TEST_CASE_METHOD(QueryFixture, "Test select sql statement string with group by",
   const auto result = select({"id", "name", "age"})
     .from("person")
     .group_by("age"_col)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT "id", "name", "age" FROM "person" GROUP BY "age")");
 }
@@ -243,7 +243,7 @@ TEST_CASE_METHOD(QueryFixture, "Test select sql statement string with offset and
     .order_by("id"_col).asc()
     .limit(20)
     .offset(10)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT "id", "name", "age" FROM "person" ORDER BY "id" ASC LIMIT 20 OFFSET 10)");
 }
@@ -259,20 +259,20 @@ TEST_CASE_METHOD(QueryFixture, "Test create, insert and select a blob column", "
     .constraints({
         constraint("PK_person").primary_key({"id"})
     })
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"##(CREATE TABLE "person" ("id" BIGINT NOT NULL, "name" VARCHAR(255) NOT NULL, "data" BLOB NOT NULL, CONSTRAINT PK_person PRIMARY KEY (id)))##");
 
   result = insert()
     .into("person", {"id", "name", "data"})
     .values({7U, "george", blob_type_t{1, 'A', 3, 4}})
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(INSERT INTO "person" ("id", "name", "data") VALUES (7, 'george', X'01410304'))");
 
   result = select({"id", "name", "data"})
     .from("person")
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT "id", "name", "data" FROM "person")");
 }
@@ -286,7 +286,7 @@ TEST_CASE_METHOD(QueryFixture, "Test select statement with join_left", "[query][
     .from(table{"flight"}.as("f"))
     .join_left(table{"airplane"}.as("ap"))
     .on(col1 == col2)
-    .str(*db);
+    .str(db->dialect());
 
   REQUIRE(result == R"(SELECT "f"."id", "ap"."brand", "f"."pilot_name" FROM "flight" "f" LEFT JOIN "airplane" "ap" ON "f"."airplane_id" = "ap"."id")");
 }
@@ -301,7 +301,7 @@ TEST_CASE_METHOD(QueryFixture, "Test select statement with join_left", "[query][
 //
 //   const auto result = select<author>(scm)
 //     .from("authors"_tab.as("T01"))
-//     .str(*db);
+//     .str(db->dialect());
 //
 //   const auto expected_sql = R"(SELECT "T01"."id", "T01"."first_name", "T01"."last_name", "T01"."date_of_birth", "T01"."year_of_birth", "T01"."distinguished" FROM "authors" "T01")";
 //

test/orm/query/QueryFixture.cpp

@@ -4,6 +4,9 @@
 
 #include "matador/sql/interface/connection_impl.hpp"
 
+#include "matador/query/basic_schema.hpp"
+#include "matador/query/schema_utils.hpp"
+
 namespace matador::test {
 
 QueryFixture::QueryFixture() {
@@ -12,4 +15,12 @@ QueryFixture::QueryFixture() {
   db = std::make_unique<sql::connection>("noop://noop.db");
 }
 
+std::unordered_map<std::type_index, query::query_contexts> QueryFixture::to_contexts_by_name(const query::basic_schema& scm, const sql::dialect& d) {
+  std::unordered_map<std::type_index, query::query_contexts> contexts_by_type;
+  for (const auto &[type, node] : scm) {
+    contexts_by_type[node.node().type_index()] = to_query_contexts(node, d);
+  }
+
+    return contexts_by_type;
+}
 }

test/orm/query/QueryFixture.hpp

@@ -3,8 +3,14 @@
 
 #include "matador/sql/connection.hpp"
 
+#include "matador/query/query_contexts.hpp"
+
 #include <memory>
 
+namespace matador::query {
+class basic_schema;
+}
+
 namespace matador::test {
 
 class QueryFixture {
@@ -12,6 +18,9 @@ public:
   QueryFixture();
   ~QueryFixture() = default;
 
+protected:
+  static std::unordered_map<std::type_index, query::query_contexts> to_contexts_by_name(const query::basic_schema& scm, const sql::dialect& d) ;
+
 protected:
   std::unique_ptr<sql::connection> db;
 };

test/orm/query/SessionQueryBuilderTest.cpp

@@ -53,7 +53,7 @@ TEST_CASE("Create sql query data for entity with eager has one", "[query][entity
   auto q = eqb.build<flight>(*col == _);
   REQUIRE(q.is_ok());
 
-  const auto sql = q->str(db);
+  const auto sql = q->str(db.dialect());
   const std::string expected_sql = R"(SELECT "t01"."id", "t02"."id", "t02"."brand", "t02"."model", "t01"."pilot_name" FROM "flights" "t01" LEFT JOIN "airplanes" "t02" ON "t01"."airplane_id" = "t02"."id" WHERE "t01"."id" = ? ORDER BY "t01"."id" ASC)";
   REQUIRE(expected_sql == sql);
 
@@ -111,7 +111,7 @@ TEST_CASE("Create sql query data for entity with eager belongs to", "[query][ent
   auto q = eqb.build<book>(*col == _);
 
   REQUIRE(q.is_ok());
-  const auto sql = q->str(db);
+  const auto sql = q->str(db.dialect());
   const std::string expected_sql = R"(SELECT "t01"."id", "t01"."title", "t02"."id", "t02"."first_name", "t02"."last_name", "t02"."date_of_birth", "t02"."year_of_birth", "t02"."distinguished", "t01"."published_in" FROM "books" "t01" LEFT JOIN "authors" "t02" ON "t01"."author_id" = "t02"."id" WHERE "t01"."id" = ? ORDER BY "t01"."id" ASC)";
   REQUIRE(expected_sql == sql);
 
@@ -188,7 +188,7 @@ TEST_CASE("Create sql query data for entity with eager has many belongs to", "[q
   auto q = eqb.build<order>(*col == _);
 
   REQUIRE(q.is_ok());
-  const auto sql = q->str(db);
+  const auto sql = q->str(db.dialect());
   const std::string expected_sql = R"(SELECT "t01"."order_id", "t01"."order_date", "t01"."required_date", "t01"."shipped_date", "t01"."ship_via", "t01"."freight", "t01"."ship_name", "t01"."ship_address", "t01"."ship_city", "t01"."ship_region", "t01"."ship_postal_code", "t01"."ship_country", "t02"."order_details_id", "t02"."order_id" FROM "orders" "t01" LEFT JOIN "order_details" "t02" ON "t01"."order_id" = "t02"."order_id" WHERE "t01"."order_id" = ? ORDER BY "t01"."order_id" ASC)";
   REQUIRE(expected_sql == sql);
 
@@ -256,7 +256,7 @@ TEST_CASE("Create sql query data for entity with eager many to many", "[query][e
   auto q = eqb.build<ingredient>(*col == _);
 
   REQUIRE(q.is_ok());
-  const auto sql = q->str(db);
+  const auto sql = q->str(db.dialect());
   const std::string expected_sql = R"(SELECT "t01"."id", "t01"."name", "t03"."id", "t03"."name" FROM "ingredients" "t01" LEFT JOIN "recipe_ingredients" "t02" ON "t01"."id" = "t02"."ingredient_id" LEFT JOIN "recipes" "t03" ON "t02"."recipe_id" = "t03"."id" WHERE "t01"."id" = ? ORDER BY "t01"."id" ASC)";
   REQUIRE(expected_sql == sql);
 
@@ -315,7 +315,7 @@ TEST_CASE("Create sql query data for entity with eager many to many (inverse par
   auto q = eqb.build<course>(*col == _);
 
   REQUIRE(q.is_ok());
-  const auto sql = q->str(db);
+  const auto sql = q->str(db.dialect());
   const std::string expected_sql = R"(SELECT "t01"."id", "t01"."title", "t03"."id", "t03"."name" FROM "courses" "t01" LEFT JOIN "student_courses" "t02" ON "t01"."id" = "t02"."course_id" LEFT JOIN "students" "t03" ON "t02"."student_id" = "t03"."id" WHERE "t01"."id" = ? ORDER BY "t01"."id" ASC)";
   REQUIRE(expected_sql == sql);
 
@@ -369,11 +369,11 @@ TEST_CASE("Test eager relationship", "[query][entity][builder]") {
 
   auto q = eqb.build<department>();
   REQUIRE(q.is_ok());
-  const auto sql = q->str(db);
+  const auto sql = q->str(db.dialect());
   const std::string expected_sql = R"(SELECT "t01"."id", "t01"."name", "t02"."id", "t02"."first_name", "t02"."last_name", "t02"."dep_id" FROM "departments" "t01" LEFT JOIN "employees" "t02" ON "t01"."id" = "t02"."dep_id" ORDER BY "t01"."id" ASC)";
   REQUIRE(expected_sql == sql);
 
-  const auto& data = eqb.query_data();
+  // const auto& data = eqb.query_data();
 
 
   // auto ctx = query::select(data.columns)
@@ -401,7 +401,7 @@ TEST_CASE("Test has one lazy relationship", "[query][entity][builder][has_one][l
 
   auto q = eqb.build<user>();
   REQUIRE(q.is_ok());
-  const auto sql = q->str(db);
+  const auto sql = q->str(db.dialect());
   const std::string expected_sql = R"(SELECT "t01"."id", "t01"."name", "t01"."password" FROM "users" "t01" ORDER BY "t01"."id" ASC)";
 
   REQUIRE(expected_sql == sql);
@@ -421,7 +421,7 @@ TEST_CASE("Test has one eager relationship", "[query][entity][builder][has_one][
 
   auto q = eqb.build<country>();
   REQUIRE(q.is_ok());
-  const auto sql = q->str(db);
+  const auto sql = q->str(db.dialect());
   const std::string expected_sql = R"(SELECT "t01"."id", "t01"."name", "t02"."id", "t02"."name", "t02"."country_id" FROM "countries" "t01" LEFT JOIN "capitals" "t02" ON "t01"."id" = "t02"."country_id" ORDER BY "t01"."id" ASC)";
 
   REQUIRE(expected_sql == sql);