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Fix UpdateModelMixin to work when no queryset is defined is defined on the view #9314

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Fix UpdateModelMixin to work when no queryset is defined is defined on the view #9314

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11 changes: 6 additions & 5 deletions rest_framework/mixins.py
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Original file line number Diff line number Diff line change
Expand Up @@ -69,13 +69,14 @@ def update(self, request, *args, **kwargs):
serializer.is_valid(raise_exception=True)
self.perform_update(serializer)

queryset = self.filter_queryset(self.get_queryset())
if queryset._prefetch_related_lookups:
if hasattr(instance, '_prefetched_objects_cache'):
Comment on lines -73 to +72
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When only get_object is defined, I assume that folks are unlikely to have advanced prefetches in their method (although it's very much possible).

If some things were prefetched, we assume that there is a get_queryset method.

# If 'prefetch_related' has been applied to a queryset, we need to
# forcibly invalidate the prefetch cache on the instance,
# and then re-prefetch related objects
# forcibly invalidate the prefetch cache on the instance
instance._prefetched_objects_cache = {}
prefetch_related_objects([instance], *queryset._prefetch_related_lookups)
queryset = self.filter_queryset(self.get_queryset())
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This is still expecting get_queryset or queryset to be defined and will raise an AssertError if it is not, which means it will still not be backwards compatabile with 3.14 correct?

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@yuekui yuekui Mar 21, 2024 •
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How is it possible that self has '_prefetched_objects_cache' defined without defining queryset or get_queryset?

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@browniebroke browniebroke Mar 21, 2024 •
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That's what I meant by my comment earlier, one might do:

class UserRetrieveWithoutQuerySet(generics.RetrieveUpdateAPIView):
    serializer_class = UserSerializer

    def get_object(self):
        return User.objects.prefetch_related('groups').get(pk=self.kwargs['pk'])

In such case, I would argue that it's reasonable to require users to override the get_queryset method... The error message says exactly that. Would probably need to be documented better, though.

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Probably just an extra if statement or try catch would solve all these cases.

if getattr(queryset, '_prefetch_related_lookups', None):
# And then re-prefetch related objects
prefetch_related_objects([instance], *queryset._prefetch_related_lookups)

return Response(serializer.data)

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15 changes: 15 additions & 0 deletions tests/test_prefetch_related.py
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,13 @@ class UserUpdateWithoutPrefetchRelated(generics.UpdateAPIView):
serializer_class = UserSerializer


class UserRetrieveWithoutQuerySet(generics.RetrieveUpdateAPIView):
serializer_class = UserSerializer

def get_object(self):
return User.objects.get(pk=self.kwargs['pk'])


class TestPrefetchRelatedUpdates(TestCase):
def setUp(self):
self.user = User.objects.create(username='tom', email='tom@example.com')
Expand Down Expand Up @@ -90,3 +97,11 @@ def test_db_query_count(self):
)
with self.assertNumQueries(16):
UserUpdateWithoutPrefetchRelated.as_view()(request, pk=self.user.pk)

def test_can_update_without_queryset(self):
request = factory.patch('/', {'username': 'new'})
response = UserRetrieveWithoutQuerySet.as_view()(request, pk=self.user.pk)
assert response.data['id'] == self.user.id
assert response.data['username'] == 'new'
self.user.refresh_from_db()
assert self.user.username == 'new'
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