implemented lazy loading for object_ptr and belongs_to

test/backends/QueryBasicTest.cpp

@@ -79,7 +79,7 @@ TEST_CASE_METHOD(QueryFixture, "Insert and select basic datatypes", "[query][dat
       .from("types")
       .fetch_one<types>(db);
     REQUIRE(result.is_ok());
-    REQUIRE(*result != nullptr);
+    REQUIRE(result->get() != nullptr);
 
     REQUIRE((*result)->id_ == 1);
     REQUIRE((*result)->char_ == cval);
@@ -356,7 +356,7 @@ TEST_CASE_METHOD(QueryFixture, "Test primary key", "[query][primary key]") {
     .from("pk")
     .fetch_one<pk>(db);
   REQUIRE(row.is_ok());
-  REQUIRE(*row != nullptr);
+  REQUIRE(row->get() != nullptr);
   REQUIRE(row.value()->id > 0);
 }
 
@@ -386,7 +386,7 @@ TEST_CASE_METHOD(QueryFixture, "Test primary key prepared", "[query][primary key
 
   auto row = stmt->fetch_one<pk>();
   REQUIRE(row.is_ok());
-  REQUIRE(*row != nullptr);
+  REQUIRE(*row);
   REQUIRE(row.value()->id > 0);
   REQUIRE(row.value()->name == "george");
 }