GenericForeignKeys lose the assigned unsaved object after the object is saved

[Willem Van Onsem]

As mentioned on ​StackOverflow, a ForeignKey can still save an object if the object was not saved when setting the model object, like:

one = Model_One()
two = Model_Two(model_one=one)
one.save()
two.save()

But this is not the case for a GenericForeignKey with:

one = Model_One()
two = Model_With_GFK(content_object=one)
one.save()
two.save()

This is because the content_object *immediately* sets the content type field and the foreign key field when setting the object, and then leaves is that way.

Perhaps overkill, but it might be worth to do the same for a ForeignKey and thus check if the object has been given .pk, and if so, set the foreign key field.

[Sarah Boyce]

Thank you for the report!

Here is a potential test. The tagged_item.save() call currently raises an error django.db.utils.IntegrityError: NOT NULL constraint failed: generic_relations_taggeditem.object_id

tests/generic_relations/tests.py

@@ -626 +626 @@
         with self.assertRaisesMessage(ValueError, msg):
             tagged_item.save()
 
+    def test_unsaved_generic_foreign_key_save(self):
+        quartz = Mineral(name="Quartz", hardness=7)
+        tagged_item = TaggedItem(tag="shiny", content_object=quartz)
+        quartz.save()
+        tagged_item.save()
+        self.assertEqual(tagged_item.content_object, quartz)
+
     @skipUnlessDBFeature("has_bulk_insert")
     def test_unsaved_generic_foreign_key_parent_bulk_create(self):

[Willem Van Onsem]

Probably we should also do a .refresh_from_db() since the GenericForeignKey probably does some caching :).

[Brock Smickley]

Replying to Sarah Boyce:

Thank you for the report!

Here is a potential test. The tagged_item.save() call currently raises an error django.db.utils.IntegrityError: NOT NULL constraint failed: generic_relations_taggeditem.object_id

tests/generic_relations/tests.py

@@ -626 +626 @@
         with self.assertRaisesMessage(ValueError, msg):
             tagged_item.save()
 
+    def test_unsaved_generic_foreign_key_save(self):
+        quartz = Mineral(name="Quartz", hardness=7)
+        tagged_item = TaggedItem(tag="shiny", content_object=quartz)
+        quartz.save()
+        tagged_item.save()
+        self.assertEqual(tagged_item.content_object, quartz)
+
     @skipUnlessDBFeature("has_bulk_insert")
     def test_unsaved_generic_foreign_key_parent_bulk_create(self):

wait, do we actually want this test to pass? or do we want a similar test with a ForeignKey to fail?

[YashRaj1506]

My question here is, having Foreignkey keep a unsaved object, is this a behaviour we should keep? should this raise a error too when saved with save() ? or we need to adapt the behaviour of genericforeignkeys so that it can also keep an unsaved object? I just looked at this ticket, so i lack a bit more deeper depth into this problem. I will do my research but i am open to other peoples opinion on this.