Union queryset should raise on distinct().

[Sielc Technologies]

After using

• .annotate() on 2 different querysets
• and then .union()
• .distinct() will not affect the queryset

    def setUp(self) -> None:
        user = self.get_or_create_admin_user()

        Sample.h.create(user, name="Sam1")
        Sample.h.create(user, name="Sam2 acid")
        Sample.h.create(user, name="Sam3")
        Sample.h.create(user, name="Sam4 acid")

        Sample.h.create(user, name="Dub")
        Sample.h.create(user, name="Dub")
        Sample.h.create(user, name="Dub")

        self.user = user

    def test_union_annotated_diff_distinct(self):
        qs = Sample.objects.filter(user=self.user)
        qs1 = qs.filter(name='Dub').annotate(rank=Value(0, IntegerField()))
        qs2 = qs.filter(name='Sam1').annotate(rank=Value(1, IntegerField()))
        qs = qs1.union(qs2)
        qs = qs.order_by('name').distinct('name')  # THIS DISTINCT DOESN'T WORK
        self.assertEqual(qs.count(), 2)

expected to get wrapped union

    SELECT DISTINCT ON (siebox_sample.name) * FROM (SELECT ... UNION SELECT ...) AS siebox_sample

[Mariusz Felisiak]

distinct() is not supported but doesn't raise an error yet. As ​​per the documentation, "only LIMIT, OFFSET, COUNT(*), ORDER BY, and specifying columns (i.e. slicing, count(), order_by(), and values()/values_list()) are allowed on the resulting QuerySet.".

Follow up to #27995.

[Mariusz Felisiak]

​PR

[GitHub <noreply@…>]

In 01a381cc:

Fixed #31580 -- Added error messages on distinct() following union(), intersection(), and difference().