Composite primary key subquery lookup prevent usage or specify fields and are not implemented for exact

[Simon Charette]

I started playing with tuple lookup support for composite primary key and I noticed two main problems.

First pk__in=query lookups completely disallow specifying which fields should be used in the select clause of the right-hand-side and implicitly set them to the left-hand-side name which assumes the same set of left-hand-side field name is shared by the right-hand-side which is a bad assumption

tests/composite_pk/models/tenant.py

@@ -44 +44 @@
         related_name="comments",
     )
     text = models.TextField(default="", blank=True)
+    integer = models.IntegerField(default=0)
 
 
 class Post(models.Model):

tests/composite_pk/test_filter.py

@@ -182 +182 @@
                     Comment.objects.filter(pk__in=pks).order_by("pk"), objs
                 )
 
+    def test_filter_comments_by_pk_in_subquery(self):
+        self.assertSequenceEqual(
+            Comment.objects.filter(
+                pk__in=Comment.objects.filter(pk=self.comment_1.pk),
+            ),
+            [self.comment_1],
+        )
+        self.assertSequenceEqual(
+            Comment.objects.filter(
+                pk__in=Comment.objects.filter(pk=self.comment_1.pk).values(
+                    "tenant_id", "id"
+                ),
+            ),
+            [self.comment_1],
+        )
+        self.comment_2.integer = self.comment_1.id
+        self.comment_2.save()
+        self.assertSequenceEqual(
+            Comment.objects.filter(
+                pk__in=Comment.objects.values("tenant_id", "integer"),
+            ),
+            [self.comment_1],
+        )
+
     def test_filter_comments_by_user_and_order_by_pk_asc(self):
         self.assertSequenceEqual(
             Comment.objects.filter(user=self.user_1).order_by("pk"),

Allowing fields to be specified requires lifting a QuerySet ​resolving time constraint which was entirely by-passable by passing queryset.query instead as the right-hand-side.

The tuple exact lookup should also allow querysets with a single element to be specified as right-hand-side which is currently disallowed

tests/composite_pk/test_filter.py

@@ -450 +474 @@
         with self.assertRaisesMessage(ValueError, msg):
             Comment.objects.filter(pk=pk)
 
+    def test_filter_comments_by_pk_exact_subquery(self):
+        self.assertSequenceEqual(
+            Comment.objects.filter(
+                pk=Comment.objects.filter(pk=self.comment_1.pk)[:1],
+            ),
+            [self.comment_1],
+        )
+        self.assertSequenceEqual(
+            Comment.objects.filter(
+                pk__in=Comment.objects.filter(pk=self.comment_1.pk).values(
+                    "tenant_id", "id"
+                )[:1],
+            ),
+            [self.comment_1],
+        )
+        self.comment_2.integer = self.comment_1.id
+        self.comment_2.save()
+        self.assertSequenceEqual(
+            Comment.objects.filter(
+                pk__in=Comment.objects.values("tenant_id", "integer"),
+            )[:1],
+            [self.comment_1],
+        )
+
     def test_outer_ref_not_composite_pk(self):
         subquery = Comment.objects.filter(pk=OuterRef("id")).values("id")
         queryset = Comment.objects.filter(id=Subquery(subquery))

Lastly lifting the constraint that prevented subqueries returning more than one column from being used as a right-hand-side required adjusting the existing exact and in lookup logic to disallow left-hand-side and right-hand-side with mismatching number of fields.

[Sarah Boyce]

Thank you!