implemented lazy loading for object_ptr and belongs_to

test/models/author.hpp

@@ -12,6 +12,13 @@ namespace matador::test {
 struct book;
 
 struct author {
+  author() = default;
+  author(const unsigned int id, std::string first_name, std::string last_name, std::string date_of_birth, const unsigned short year_of_birth, const bool distinguished)
+  : id(id), first_name(std::move(first_name))
+  , last_name(std::move(last_name))
+  , date_of_birth(std::move(date_of_birth))
+  , year_of_birth(year_of_birth)
+  , distinguished(distinguished) {}
   unsigned int id{};
   std::string first_name;
   std::string last_name;