implemented lazy loading for object_ptr and belongs_to

include/matador/sql/internal/statement_object_resolver.hpp

@@ -0,0 +1,35 @@
+#ifndef MATADOR_STATEMENT_OBJECT_RESOLVER_HPP
+#define MATADOR_STATEMENT_OBJECT_RESOLVER_HPP
+
+#include "matador/object/object_resolver.hpp"
+
+#include "matador/sql/statement.hpp"
+#include "matador/sql/internal/identifier_statement_binder.hpp"
+
+namespace matador::sql {
+template<typename Type>
+class statement_object_resolver : public object::object_resolver<Type> {
+public:
+  explicit statement_object_resolver(statement stmt)
+  : statement_(std::move(stmt)) {}
+
+  std::shared_ptr<Type> resolve(const utils::identifier &id) override;
+protected:
+  statement statement_;
+  std::type_index index{typeid(Type)};
+};
+
+template<typename Type>
+std::shared_ptr<Type> statement_object_resolver<Type>::resolve(const utils::identifier &id) {
+  identifier_statement_binder binder(statement_);
+  binder.bind(id);
+
+  auto result = statement_.template fetch_one<Type>();
+  if (!result) {
+    return nullptr;
+  }
+  return std::make_shared<Type>(*result);
+}
+
+}
+#endif //MATADOR_STATEMENT_OBJECT_RESOLVER_HPP