ValueError not raised when wrong number of columns selected by subquery against composite primary key

[Jacob Walls]

Discovered during ​review of #36210 that the guard for the appropriate number of columns selected in a subquery is not aware that "pk" might represent N columns, so the ValueError that should be raised is evaded, failing instead at the db layer.

We're just changing one type of exception to another--so this isn't terribly serious--but in the interest of standardizing what kinds of exceptions are raised during usage of the composite pk feature, starting out at release blocker?

tests/composite_pk/test_filter.py

@@ -207 +207 @@
             [self.comment_1],
         )
 
+    def test_invalid_filter_by_pk_in_columns_besides_pk(self):
+        with self.assertRaisesMessage(ValueError, "must have 2 selected fields"):
+            User.objects.filter(pk__in=User.objects.values("pk", "email")).count()
+
     def test_filter_by_pk_in_none(self):
         with self.assertNumQueries(0):
             self.assertSequenceEqual(

---

Postgres failure looks like:

  File "/Users/.../django/django/db/backends/sqlite3/base.py", line 360, in execute
    return super().execute(query, params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
django.db.utils.OperationalError: sub-select returns 3 columns - expected 2

[Jacob Walls]

​PR

[Sarah Boyce <42296566+sarahboyce@…>]

In 994dc6d8:

Fixed #36392 -- Raised ValueError when subquery referencing composite pk selects too many columns.

[Sarah Boyce <42296566+sarahboyce@…>]

In 6228a35:

[5.2.x] Fixed #36392 -- Raised ValueError when subquery referencing composite pk selects too many columns.

Backport of 994dc6d8a1bae717baa236b65e11cf91ce181c53 from main.