distinct(*fields) does not fathom aliases containing the lookup separator: "__"

[Jacob Walls]

We are gradually improving the situation with respect to the treatment of annotation aliases containing the lookup separator, see ​PR discussion. This ticket is for .distinct(*fields).

When an alias is provided to .distinct(*fields), is it split on LOOKUP_SEP before checking against the annotations map, meaning it will miss an alias that contains it.

Reproducer:

qs = Person.objects.annotate(my__val=models.Value(1)).distinct("my__val")
print(qs)

  File "/django-ref/django/db/models/sql/query.py", line 1854, in names_to_path
    raise FieldError(
django.core.exceptions.FieldError: Cannot resolve keyword 'my' into field. Choices are: id, my__val, name

The helper from 73cc09f14f13fedddc14d6ba5b287cb33c24e4a4 could be used as part of fixing this, so that we don't omit any nuance with FilteredRelation.

Using the lookup separator in an annotation alias sounds a little unorthodox, but it's present in the ​default alias generated by .aggregate(), and we've taken reports on it before. Also, if you let users choose aliases in configurable reports, it's bound to come up, and we've taken issues on that.

[Jacob Walls]

Juliana took this on at Django on the Med 2026 in Pescara and almost has a PR ready to go.

[Juliana Nicacio]

PR -> ​https://github.com/django/django/pull/22044

[Jacob Walls <jacobtylerwalls@…>]

In dffadf6d:

Fixed #37350 -- Made distinct(*fields) resolve aliases containing "".

Made Query.get_names_to_join() preserve annotation aliases and used it
in SQLCompiler.get_distinct() instead of splitting on LOOKUP_SEP.

Thanks Jacob Walls for the report and the suggested approach, and
Annabelle Wiegart for the groundwork in #36945.