diff --git a/django/db/models/query.py b/django/db/models/query.py index 343f4dc718..55a94cebe5 100644 --- a/django/db/models/query.py +++ b/django/db/models/query.py @@ -1538,7 +1538,12 @@ def prefetch_one_level(instances, prefetcher, lookup, level): # contains some prefetch_related lookups. We don't want to trigger the # prefetch_related functionality by evaluating the query. Rather, we need # to merge in the prefetch_related lookups. - additional_lookups = getattr(rel_qs, '_prefetch_related_lookups', []) + # Copy the lookups in case it is a Prefetch object which could be reused + # later (happens in nested prefetch_related). + additional_lookups = [ + copy.copy(additional_lookup) for additional_lookup + in getattr(rel_qs, '_prefetch_related_lookups', []) + ] if additional_lookups: # Don't need to clone because the manager should have given us a fresh # instance, so we access an internal instead of using public interface diff --git a/tests/prefetch_related/tests.py b/tests/prefetch_related/tests.py index f059a6f7ca..d9e7488d42 100644 --- a/tests/prefetch_related/tests.py +++ b/tests/prefetch_related/tests.py @@ -626,6 +626,17 @@ class CustomPrefetchTests(TestCase): room = Room.objects.filter(main_room_of__isnull=False).prefetch_related(Prefetch('main_room_of', queryset=houses.filter(address='DoesNotExist'), to_attr='main_room_of_attr')).first() self.assertIsNone(room.main_room_of_attr) + def test_nested_prefetch_related_are_not_overwritten(self): + # Regression test for #24873 + houses_2 = House.objects.prefetch_related(Prefetch('rooms')) + persons = Person.objects.prefetch_related(Prefetch('houses', queryset=houses_2)) + houses = House.objects.prefetch_related(Prefetch('occupants', queryset=persons)) + list(houses) # queryset must be evaluated once to reproduce the bug. + self.assertEqual( + houses.all()[0].occupants.all()[0].houses.all()[1].rooms.all()[0], + self.room2_1 + ) + class DefaultManagerTests(TestCase):