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 20932 Issues with model Manager and inheritance. loic84 nobody "I've found a couple of issues with the current handling of managers with inheritance. 1. Given: {{{#!python class AbstractEvent(models.Model): events = models.Manager() class Meta: abstract = True class BachelorParty(AbstractEvent): objects = models.Manager() class MessyBachelorParty(BachelorParty): pass }}} If `AbstractEvent` has a manager called anything but `objects` (e.g. `events`): `MessyBachelorParty.objects.model == ` Which causes the following failure: {{{ model_inheritance_regress.tests.ModelInheritanceTest.test_abstract_base_class_m2m_relation_inheritance` fails with `AttributeError: 'BachelorParty' object has no attribute 'bachelorparty_ptr'. }}} If `AbstractEvent` doesn't have an explicit manager, or has one called `objects`: `MessyBachelorParty.objects.model == ` which is the expected result. 2. Managers in MTI *are* inherited, contrary to what is said [https://docs.djangoproject.com/en/dev/topics/db/managers/#custom-managers-and-model-inheritance in the docs] (now tracked specifically in #25897): ""Managers defined on non-abstract base classes are not inherited by child classes. [...] Therefore, they aren’t passed onto child classes."". The problem is that, since we create the new class by calling `object.__new__()`, normal Python attribute resolution applies, and we gain access to the attributes of the base classes. This doesn't happen to fields because these are removed during the class creation process, but managers are left behind. It's always tempting to think we could just delete them, but you cannot delete something that is not in your own `__dict__`. The problem is not so much that we inherit those managers, but that they don't return the right model type as demonstrated in https://github.com/loic/django/compare/manager_inheritance_bug2." Bug closed Database layer (models, ORM) dev Normal fixed manager-inheritance Anssi Kääriäinen LaurensBER aronp@… Marc Tamlyn Ready for checkin 1 0 0 0 0 0