Loosen tuple lookup check for rhs subquery field cardinality to allow selecting ForeignObject

[Jacob Walls]

As of the fix for #36431, values("user") where "user" is a multi-column ForeignObject now resolves to a Tuple, which means we can relax the cardinality check for lookups such as TupleIn (introduced in #36149) to get this test case passing:

tests/composite_pk/test_filter.py

@@ -460 +460 @@
         queryset = User.objects.filter(comments__in=subquery)
         self.assertSequenceEqual(queryset, (self.user_2,))
 
+    def test_filter_comments_by_users_subquery(self):
+        subquery = Comment.objects.filter(id=3).values("user")
+        queryset = Comment.objects.filter(user__in=subquery)
+        self.assertSequenceEqual(queryset, (self.comment_3,))
+
     def test_cannot_cast_pk(self):
         msg = "Cast expression does not support composite primary keys."
         with self.assertRaisesMessage(ValueError, msg):

Currently this gives:

  File "/Users/jwalls/django/django/db/models/fields/related_lookups.py", line 84, in get_prep_lookup
    return super().get_prep_lookup()
           ~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/Users/jwalls/django/django/db/models/lookups.py", line 509, in get_prep_lookup
    raise ValueError(
    ...<2 lines>...
    )
ValueError: The QuerySet value for the 'in' lookup must have 2 selected fields (received 1)

----------------------------------------------------------------------

Indeed, commenting out that ValueError allows this test to pass with the fix for #36431, so there should be way to adjust this guard.

[Natalia Bidart]

Thank you Jacob for the details!

[GitHub <noreply@…>]

In 23b6594:

Fixed #36584, Refs #36149 -- Allowed subquery values against tuple in lookup via ForeignObject.