id,summary,reporter,owner,description,type,status,component,version,severity,resolution,keywords,cc,stage,has_patch,needs_docs,needs_tests,needs_better_patch,easy,ui_ux 28856,GenericForeignKey attributes create new instances on every access,Morgan Wahl,nobody,"Given these models: {{{ class OtherSuper(models.Model): pass class OtherSub(OtherSuper): pass class Ref(models.Model): obj_type = models.ForeignKey(ContentType, on_delete=models.PROTECT) obj_id = models.CharField(max_length=255) obj = GenericForeignKey('obj_type', 'obj_id') }}} I get this behavior: {{{ In [1]: ref = Ref.objects.create(obj=OtherSub.objects.create()) In [2]: id(ref.obj) == id(ref.obj) Out[2]: True In [3]: ref.refresh_from_db() In [4]: id(ref.obj) == id(ref.obj) Out[4]: False }}} Each time `ref.obj` is accessed, a new instance is created for its value. This is a problem, since doing something like `ref.obj.field = 1; ref.obj.save()` won't actually update the field in the database. This only happens when the referenced object is an instance of a model that subclasses another model. (So, it wouldn't happen if referencing `OtherSuper` in the models above.) The `refresh_from_db()` call is also necessary to reproduce this in a simple test like the above; it happens with any instance created from an existing DB record. I've written a regression test against stable/1.10.x . I'll attach a patch. I discovered this because I have code that does the above (changes a field on the related model and calls save). I call this a regression because it works correctly on 1.9. I'm not sure what the underly bug is; I looked at the diff in `contenttypes` between 1.9 and 1.10, and there are more than a few changes. Hopefully someone who understands the `GenericForeignKey` implementation can figure this out.",Bug,closed,contrib.contenttypes,1.10,Normal,fixed,,,Accepted,1,0,0,0,0,0