BaseModelFormSet could leverage totally_ordered property

[Jacob Walls]

#36857 added a new property totally_ordered on QuerySet to capture the difference between a queryset having some ordering versus a "stable, deterministic" ordering.

I noticed that we probably want to use that new property here in BaseModelFormSet for the purpose described in #10163:

django/forms/models.py

@@ -776 +776 @@
             # If the queryset isn't already ordered we need to add an
             # artificial ordering here to make sure that all formsets
             # constructed from this queryset have the same form order.
-            if not qs.ordered:
+            if not qs.totally_ordered:
                 qs = qs.order_by(self.model._meta.pk.name)
 
             # Removed queryset limiting here. As per discussion re: #13023

Tentatively assigning to Sarah to see if a good fit for any Djangonauts this session. This would involve cooking up a test.

[Rodrigo Vieira]

Hi, I'm a Djangonaut (Session 6) and if the author of #36857 or anyone else is not available/interested I'd like to give it a go, seems to be mostly making the change proposed and a few tests?

[Simon Charette]

Go for it Rodrigo!

We'll likely want to augment the ordering with pk here and not entirely replace it (​just like serializers do) otherwise it might break the natural ordering expected by users (e.g inlines ordered by name or publish date) so the proposed patch will need a bit of tweaking.

order_by also accepts "pk" so we can avoid model introspection here; self.model._meta.pk.name -> "pk".

[Rodrigo Vieira]

Thanks for the pointers Simon! ​PR is here, following the same pattern as the code you pointed out in serializers. I added one test for each "branch" of the checks.

[Jacob Walls <jacobtylerwalls@…>]

In 08aa1b5a:

Refs #37004 -- Added coverage for BaseModelFormSet.get_queryset() fallback ordering.

[Jacob Walls <jacobtylerwalls@…>]

In 856c915:

Fixed #37004 -- Used QuerySet.totally_ordered in BaseModelFormSet.get_queryset() for stable ordering.