Cannot resolve OuterRef to CompositePrimaryKey

[Jacob Walls]

With CompositePrimaryKey, using OuterRef("pk") in a subquery raises ValueError. Not certain if this is a release blocker or a new feature. If it's a new feature, we might want to document that it's not currently supported.

tests/composite_pk/test_filter.py

@@ +1 @@
+from django.db.models import OuterRef, Subquery
 from django.test import TestCase
 
 from .models import Comment, Tenant, User
@@ -54 +55 @@
             with self.subTest(lookup=lookup, count=count):
                 self.assertEqual(User.objects.filter(**lookup).count(), count)
 
+    def test_outer_ref_pk(self):
+        qs = Comment.objects.filter(
+            id__gt=Subquery(Comment.objects.filter(pk=OuterRef("pk")).values("id")[:1])
+        )
+        self.assertEqual(qs.count(), 0)
+
     def test_order_comments_by_pk_asc(self):
         self.assertSequenceEqual(
             Comment.objects.order_by("pk"),

  File "/Users/.../django/django/db/models/fields/tuple_lookups.py", line 32, in get_prep_lookup
    self.check_rhs_is_tuple_or_list()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/Users/.../django/django/db/models/fields/tuple_lookups.py", line 39, in check_rhs_is_tuple_or_list
    raise ValueError(
        f"{self.lookup_name!r} lookup of {lhs_str} must be a tuple or a list"
    )
ValueError: 'exact' lookup of 'pk' must be a tuple or a list

---

Adjusting the guard that raises ValueError to also accept ResolvedOuterRef leads to a more interesting failure:

  File "/Users/.../django/django/db/models/expressions.py", line 1162, in as_sql
    val = output_field.get_db_prep_value(val, connection=connection)
  File "/Users/.../django/django/db/models/fields/related.py", line 1161, in get_db_prep_value
    return self.target_field.get_db_prep_value(value, connection, prepared)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../django/django/db/models/fields/__init__.py", line 2819, in get_db_prep_value
    value = self.get_prep_value(value)
  File "/Users/.../django/django/db/models/fields/__init__.py", line 2129, in get_prep_value
    raise e.__class__(
        "Field '%s' expected a number but got %r." % (self.name, value),
    ) from e
TypeError: Field 'id' expected a number but got Col(composite_pk_comment, composite_pk.Comment.tenant).

[Sarah Boyce]

Thank you Jacob
Marking as a release blocker. I think we might be able to resolve this but if not, agree we might want to document it within the not supported section.

[Sarah Boyce]

Note that the "document" fix can include a better error message.

[Csirmaz Bendegúz]

Thank you, I'll look into it

[Csirmaz Bendegúz]

I added a patch