prefetch_related() crashes with values_list(flat=True)

[Dotan Agmon]

Assuming these models:

class Temp(models.Model):
    pass


class TempUuid(models.Model):
    uuid = models.UUIDField(default=uuid.uuid4, editable=False)
    temp = models.ForeignKey(Temp)

The result of the following code:

>>> temp = Temp.objects.create()
>>> TempUuid.objects.create(temp=temp)
>>> TempUuid.objects.prefetch_related('temp').values_list('uuid', flat=True)

is:

TypeError: UUID objects are immutable

Note that there's no exception when removing the flat=True.

[Shai Berger]

Without flat=True, there's no exception, and the prefetch_related() call apparently has no effect. In similar cases, where optimizations no longer made sense, we simply dropped them, so this behavior seems right; in that case, that should also be the behavior with flat=True.

[Tim Graham]

Attached is a regression test for Django's test suite.

[Attila Tovt]

​PR

[Tim Graham <timograham@…>]

In 5e2c4d7a:

Fixed #26264 -- Fixed prefetch_related() crashes with values_list(flat=True)