Unable to filter against annotations in Manager with use_for_related_fields

[Ryan P Kilby]

Per the title, it seems like it would make sense to be able to filter annotations across relationships. Given the following,

from django.db import models
from django.db.models import Value as V
from django.db.models.functions import Concat


class PersonManager(models.Manager):
    use_for_related_fields = True

    def get_queryset(self):
        queryset = super(PersonManager, self).get_queryset()
        queryset = queryset.annotate(full_name=Concat(
            'first_name', V(' '), 'last_name',
            output_field=models.CharField()
        ))
        return queryset


class Person(models.Model):
    first_name = models.CharField(max_length=100)
    last_name = models.CharField(max_length=100)

    objects = PersonManager()


class Article(models.Model):
    published = models.DateTimeField()
    author = models.ForeignKey(Person, null=True, on_delete=models.CASCADE)

Running this:

Article.objects.filter(author__full_name="Bob, just Bob")

Produced the following traceback (snipped)

  ...
  File "site-packages/django/db/models/query.py", line 790, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "site-packages/django/db/models/query.py", line 808, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "site-packages/django/db/models/sql/query.py", line 1243, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "site-packages/django/db/models/sql/query.py", line 1269, in _add_q
    allow_joins=allow_joins, split_subq=split_subq,
  File "site-packages/django/db/models/sql/query.py", line 1192, in build_filter
    raise FieldError('Related Field got invalid lookup: {}'.format(lookups[0]))
FieldError: Related Field got invalid lookup: full_name

[Tim Graham]

I think you have a misunderstanding of how use_for_related_fields works. The queryset in the custom manager isn't used in a query like Article.objects.filter(...) is it? If I'm missing something obvious and you have a patch demonstrating how your proposal works, then please reopen the ticket with details.

[Ryan P Kilby]

Yep - I completely misunderstood how that worked. I assumed that when filtering across relationships, the sql from the related manager was somehow used by the primary model's manager.