implemented prepared statement for postgres and sqlite

backends/postgres/src/postgres_connection.cpp

@@ -1,13 +1,17 @@
 #include "postgres_connection.hpp"
 #include "postgres_error.hpp"
 #include "postgres_result_reader.hpp"
+#include "postgres_statement.hpp"
 
 #include "matador/sql/record.hpp"
 
 #include <iostream>
+#include <sstream>
 
 namespace matador::backends::postgres {
 
+postgres_connection::string_to_int_map postgres_connection::statement_name_map_{};
+
 postgres_connection::postgres_connection(const sql::connection_info &info)
 : connection_impl(info) {}
 
@@ -47,20 +51,41 @@ std::unique_ptr<sql::query_result_impl> postgres_connection::fetch(const std::st
   throw_postgres_error(res, conn_, "postgres", stmt);
 
   sql::record prototype;
-  auto ncol = PQnfields(res);
-  for (int i = 0; i < ncol; ++i) {
+  auto num_col = PQnfields(res);
+  for (int i = 0; i < num_col; ++i) {
     const char *col_name = PQfname(res, i);
     auto type = PQftype(res, i);
     auto size = PQfmod(res, i);
-    std::cout << "column " << col_name << ", type " << type << " (size: " << size << ")\n";
+//    std::cout << "column " << col_name << ", type " << type << " (size: " << size << ")\n";
     prototype.append({col_name});
   }
   return std::move(std::make_unique<sql::query_result_impl>(std::make_unique<postgres_result_reader>(res), std::move(prototype)));
 }
 
-void postgres_connection::prepare(const std::string &stmt)
+std::string postgres_connection::generate_statement_name(const sql::query_context &query)
 {
+  std::stringstream name;
+  name << query.table_name << "_" << query.command_name;
+  auto result = postgres_connection::statement_name_map_.find(name.str());
 
+  if (result == postgres_connection::statement_name_map_.end()) {
+    result = postgres_connection::statement_name_map_.insert(std::make_pair(name.str(), 0)).first;
+  }
+
+  name << "_" << ++result->second;
+
+  return name.str();
+}
+
+std::unique_ptr<sql::statement_impl> postgres_connection::prepare(sql::query_context context)
+{
+  auto statement_name = postgres_connection::generate_statement_name(context);
+
+  PGresult *result = PQprepare(conn_, statement_name.c_str(), context.sql.c_str(), static_cast<int>(context.bind_vars.size()), nullptr);
+
+  throw_postgres_error(result, conn_, "postgres", context.sql);
+
+  return std::make_unique<postgres_statement>(conn_, result, statement_name, std::move(context));
 }
 
 size_t postgres_connection::execute(const std::string &stmt)