order_by() a parent model crash when Meta.ordering contains expressions.

[Jonny Fuller]

Hi friends,

During testing I discovered a strange bug when using a query expression for ordering during multi-table inheritance. You can find the full write up as well as reproducible test repository ​https://github.com/JonnyWaffles/djangoordermetabug. The bug occurs because the field is an OrderBy object, not a string, during get_order_dir. The linked stacktrace should make the issue obvious, but what I don't understand is why it only fails during test db setup, not during repl or script use. I wish I could help more and come up with a real solution. Hopefully, this is enough for someone wiser to find the culprit.

[Mariusz Felisiak]

Thanks for the report. I attached a regression test.

Reproduced at c498f088c584ec3aff97409fdc11b39b28240de9.

[Mariusz Felisiak]

Regression test.

[Alex Scott]

I *think* I'm getting a similar (or same) error when adding lowercased ordering to a model via meta:

class Recipe(models.Model):
    # ...
    class Meta:
        ordering = (Lower('name'),)

This works fine in normal views (listing out recipes for instance), but in the admin, I get the following error:
'Lower' object is not subscriptable

which also comes via get_order_dir()

[Mariusz Felisiak]

Yes that's the same issue, thanks for another scenario to reproduce it.

[Eran Keydar]

​https://github.com/django/django/pull/11489

[Mariusz Felisiak]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 8c5f9906:

Fixed #30557 -- Fixed crash of ordering by ptr fields when Meta.ordering contains expressions.

[GitHub <noreply@…>]

In 7a42cfcf:

Refs #30557 -- Fixed crash of ordering by ptr fields when Meta.ordering contains F() expressions.

Thanks Can Sarıgöl for the report.

Follow up to 8c5f9906c56ac72fc4f13218dd90bdf9bc8a248b.