implemented lazy loading for object_ptr and belongs_to

test/models/department.hpp

@@ -11,6 +11,9 @@ namespace matador::test {
 struct employee;
 
 struct department {
+    department() = default;
+    department(const unsigned int id, std::string name)
+    : id(id), name(std::move(name)) {}
     unsigned int id{};
     std::string name;
     std::vector<object::object_ptr<employee>> employees{};
@@ -27,6 +30,9 @@ struct department {
 };
 
 struct employee {
+    employee() = default;
+    employee(const unsigned int id, std::string first, std::string last, object::object_ptr<department> dep)
+    : id(id), first_name(std::move(first)), last_name(std::move(last)), dep(std::move(dep)) {}
     unsigned int id{};
     std::string first_name;
     std::string last_name;