#35434: prefetch_related_objects fails to cache UUID FKs when the string
representation of a UUID is used
-------------------------------------+-------------------------------------
Reporter: selcuk | Owner: nobody
Type: Bug | Status: new
Component: Database | Version: dev
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Consider the following models:
{{{
class Pet(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4,
editable=False)
name = models.CharField(max_length=20)
class Toy(models.Model):
pet = models.ForeignKey(Pet, models.CASCADE, related_name="toys")
name = models.CharField(max_length=20)
}}}
The following works and caches the deferred {{{pet}}} instance as
expected:
{{{
pet = Pet.objects.create(name="Fifi")
toy_bone = Toy(pet_id=str(pet.id), name="Bone")
print(toy_bone.pet)
}}}
It fails if {{{prefetch_related_objects}}} is used:
{{{
pet = Pet.objects.create(name="Fifi")
toy_bone = Toy(pet_id=str(pet.id), name="Bone")
prefetch_related_objects([toy_bone], "pet")
print(toy_bone.pet)
}}}
{{{
raise self.RelatedObjectDoesNotExist(
^^^^^^^^^^^^^^^^^
prefetch_related.models.Toy.pet.RelatedObjectDoesNotExist: Toy has no pet.
}}}
The behaviour is inconsistent as str to UUID conversion is automatically
performed in the first example.
One may argue that the use of {{{prefetch_related_objects}}} is redundant
in this case. However, it is useful in async code where deferred lookups
are not automatic.
--
Ticket URL: <https://code.djangoproject.com/ticket/35434>
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