Composite primary key exact lookups don’t support F() expressions on the RHS

[Pravin]

An exact lookup on a CompositePrimaryKey accepts a literal tuple but rejects an F() expression referencing a compatible composite primary key.

for example,

class Comment(models.Model):
    pk = models.CompositePrimaryKey("tenant_id", "id")
    tenant_id = models.IntegerField()
    id = models.IntegerField()
    text = models.TextField()

The following works.

comment = Comment.objects.first()
Comment.objects.filter(pk=(comment.tenant_id, comment.id))

but below one fails.

Comment.objects.filter(pk=models.F("pk"))

it raises
ValueError: 'exact' subquery lookup of 'pk' only supports OuterRef and QuerySet objects (received 'ColPairs')

[Sarah Boyce]

Thank you for the report! Replicated
This is potentially a quick fix but I will let you investigate further

django/db/models/fields/tuple_lookups.py

@@ -74 +74 @@
             )
 
     def check_rhs_is_supported_expression(self):
-        if not isinstance(self.rhs, (ResolvedOuterRef, Query)):
+        if not isinstance(self.rhs, (ColPairs, ResolvedOuterRef, Query)):
             lhs_str = self.get_lhs_str()
             rhs_cls = self.rhs.__class__.__name__
             raise ValueError(

tests/composite_pk/test_filter.py

@@ -75 +75 @@
         with self.assertRaisesMessage(ValueError, msg):
             Comment.objects.filter(text__gt=F("pk")).count()
 
+    def test_exact_f_expression_rhs(self):
+        self.assertQuerySetEqual(
+            Comment.objects.filter(pk=F("pk")),
+            Comment.objects.all(),
+            ordered=False,
+        )
+
     def test_rhs_combinable(self):
         msg = "CombinedExpression expression does not support composite primary keys."

[Pravin]

Thanks Sarah. Do we need to update release doc for it ? if yes then which version ?

[Sarah Boyce]

No release note needed, we won't backport this fix