Made sure that the postgres module compiles

CMakeLists.txt

@@ -58,6 +58,7 @@ target_include_directories(
     $<INSTALL_INTERFACE:include>)
 
 if (SQLGEN_POSTGRES)
+    list(APPEND SQLGEN_SOURCES src/sqlgen_postgres.cpp)
     if (NOT TARGET PostgreSQL)
         find_package(PostgreSQL REQUIRED)
     endif()

include/sqlgen/postgres/Connection.hpp

@@ -46,8 +46,12 @@ class Connection : public sqlgen::Connection {
       const std::vector<std::vector<std::optional<std::string>>>& _data) final;
 
  private:
-  static rfl::Result<Ref<sqlgen::Connection>> make_conn(
-      const std::string& _conn_str);
+  static ConnPtr make_conn(const std::string& _conn_str);
+
+ private:
+  ConnPtr conn_;
+
+  Credentials credentials_;
 };
 
 }  // namespace sqlgen::postgres

src/sqlgen_postgres.cpp

@@ -0,0 +1,2 @@
+#include "sqlgen/postgres/Connection.cpp"
+#include "sqlgen/postgres/Iterator.cpp"