Opened 50 minutes ago

Last modified 48 minutes ago

#37308 new Cleanup/optimization

Lookups on annotation aliases in .values() and .order_by() resolve unexpectedly

Reported by: Annabelle Wiegart Owned by:
Component: Database layer (models, ORM) Version: 6.1
Severity: Normal Keywords: alias, values, order_by
Cc: Annabelle Wiegart Triage Stage: Unreviewed
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

Doing a lookup on an annotation alias results in an unexpected name resolution. When calling e.g. .values(alias + "__pk"), Query.names_to_path() checks if f"{alias}__pk" is the name of an annotation. Otherwise it tries to resolve the name into field plus lookup. This might be unexpected. While allowing lookups on aliases may add too much complexity and therefore not be desirable, it would probably be helpful to at least show a warning when .values() or .order_by() is called on an expression containing an alias name and __.

The issue has been discussed in ​PR21803 for #36945.

​ORM fiddle

Reproducer:

from django.db import models
from django.contrib.auth.models import User
from django.contrib.contenttypes.models import ContentType


class Person(models.Model):
    name = models.CharField(max_length=100)
    creator = models.ForeignKey(User, models.CASCADE, null=True)
    ct = models.ForeignKey(ContentType, models.CASCADE)


def run():
    admin = User.objects.create(username='admin')
    person_ct = ContentType.objects.get_for_model(Person)
    Person.objects.create(creator=admin, name="Claude", ct=person_ct)
    # resolves correctly
    qs1 = Person.objects.all().values("creator__pk")
    print(qs1)
    
    alias = "myalias"
    # raises FieldError
    qs2 = Person.objects.annotate(**{alias: models.F("creator")}).values(alias + "__pk")
    print(qs2)
    # raises FieldError
    qs3 = Person.objects.annotate(
        **{alias: models.FilteredRelation("creator", condition=models.Q(creator__isnull=False))}
    ).values(alias + "__pk")
    print(qs3)

Output:

django.core.exceptions.FieldError: Cannot resolve keyword 'myalias' into field. Choices are: creator, creator_id, ct, ct_id, id, name

Change History (1)

comment:1 by Annabelle Wiegart, 48 minutes ago

Type: Uncategorized → Cleanup/optimization
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