OuterRef not resolved as part of ORDER BY clause

[REGNIER Guillaume]

I feel like OuterRef are not resolved properly where used for ordering.

Here is a simple example showcasing the issue:

MyModel.objects.annotate(foo=Subquery(MyModel.objects.order_by("pk" - OuterRef("pk")).values("pk")[:1]))

The above fails with :
ValueError: This queryset contains a reference to an outer query and may only be used in a subquery.
Because the as_sql method of ResolvedOuterRef is called.

I think this a bug because it did not raise any notice regarding OuterRef and order_by not being compatible.

[David Sanders]

Thanks 👍

Just FYI this will work (note you must wrap 'pk' with an F):

MyModel.objects.annotate(foo=Subquery(MyModel.objects.annotate(order=F("pk") - OuterRef("pk")).order_by("order").values("pk")[:1]))

[Jordan Bae]

I will try to fix this!

[REGNIER Guillaume]

I've been working in and out on this for the last three weeks. I'm sorry I didn't claim the ticket...

Here is a branch where the issue is solved: ​https://github.com/Alombaros/django/tree/ticket_34533_3_2

I'm unsure on how to proceed.
Previously, in the following query :
MyModel.objects.annotate(foo=Subquery(MyOtherModel.objects.order_by(F("pk")).values("pk")[:1]))
The F("pk") was resolved as the pk of the outer query (MyModel in this case) which does not seems right to me.
This was due to the order by expressions not being resolved until the last minute.

I force the resolution when annotating a SubQuery so that the OuterRef can do its job but this made so F objects are resolved as field of the inner query.
To me, this seems to be closer to the intended behavior because its what append when calling .filter or .annotate but if anyone used the prior behavior, thing will break

[Jordan Bae]

no worry! i think it's better tyou bring this ticket. i deassign this ticket.

[Umang Patel]

​https://github.com/django/django/pull/17326

[Mariusz Felisiak]

​PR

[Shafiya Adzhani]

I will try to improve what can be done from previous PR.

[Simon Charette]

The hard part is here is likely due to two factor

1. OuterRef resolving is quite finicky and depends on a specific chain of resolving during query composition (subquery is resolved and then the outer query is)
2. order_by members are unfortunately not resolved at query composition time (when QuerySet.order_by is called) but ​at query compilation time.

The reason for 2. is that QuerySet.order_by calls are not additive but destructive and that the query composition logic doesn't support a generic way of eliding joins that we previously created for some operations.

For example, say that you have a query that does qs = Book.objects.order_by("author__name"). If the order by clause is immediately resolved then a JOIN to author must be created. If the same query has then its ordering changed to qs.order_by("title") then we'd want to clear the join to author as it's no longer necessary.

In order to avoid implementing the logic to unreference relations the order_by method deferred the resolving to the very end of query compilation which is a different path than the normal resolving taking place in additive methods such as annotate and filter.

I suspect this ticket will be hard to solve without tackling the large problem of compile time resolving of order_by.

[Shafiya Adzhani]

Replying to Simon Charette:

The hard part is here is likely due to two factor

1. OuterRef resolving is quite finicky and depends on a specific chain of resolving during query composition (subquery is resolved and then the outer query is)
2. order_by members are unfortunately not resolved at query composition time (when QuerySet.order_by is called) but ​at query compilation time.

The reason for 2. is that QuerySet.order_by calls are not additive but destructive and that the query composition logic doesn't support a generic way of eliding joins that we previously created for some operations.

For example, say that you have a query that does qs = Book.objects.order_by("author__name"). If the order by clause is immediately resolved then a JOIN to author must be created. If the same query has then its ordering changed to qs.order_by("title") then we'd want to clear the join to author as it's no longer necessary.

In order to avoid implementing the logic to unreference relations the order_by method deferred the resolving to the very end of query compilation which is a different path than the normal resolving taking place in additive methods such as annotate and filter.

I suspect this ticket will be hard to solve without tackling the large problem of compile time resolving of order_by.

Thank you for the pointer! Since this ticket is complicated, I'll leave it to someone who is interested in solving this problem.

[HeejunShin]

could i try fix this ticket?

[David Sanders]

You're welcome to try with the disclaimer that you understand what Simon has said above about it being quite hard and it will take an in-depth understanding of how expressions are resolved & compiled :)

[HeejunShin]

Thank you for answer.

I have a question.
Has this error been resolved in version 4.0 or higher?

[bcail]

@HeejunShin, you can try running the example from the ticket Description - see if that works with the main branch. I don't think this issue has been fixed, though.

[Chris M]

I am able to reproduce this issue with a simple unit test still against the main branch.

tests/queries/tests.py

@@ -2377 +2377 @@
         NamedCategory.objects.create(id=3, name="third")
         NamedCategory.objects.create(id=4, name="fourth")
 
+    def test_outer_ref_order_by(self):
+        values = NamedCategory.objects.annotate(
+            foo=NamedCategory.objects.order_by(OuterRef("pk").desc()).values("name")
+        ).first()
+
+        self.assertEqual(["fourth", "third", "second", "first"], values.foo)
+
     def test_ordered_subselect(self):
         "Subselects honor any manual ordering"
         query = DumbCategory.objects.filter(

[Ayush Khatri]

​https://github.com/django/django/pull/18878

[Jacob Walls]

Thanks for linking the PR, Ayush, and when assuming a ticket you can unset Patch Needs Improvement to ensure you get an initial review.