Admin changelist crashes when using query expression in the model's Meta.ordering or ModelAdmin.ordering

[Gabriel Amram]

Using the newly introduced query-expression ordering feature in either the model's Meta.ordering or in its ModelAdmin causes errors.

Steps to reproduce:
First variant - using the model's Meta.ordering option -

//models.py
class Game(models.Model):
    score = models.IntegerField(null=True)

     class Meta:
         ordering = [F("score").desc(nulls_last=True)]
...
// admin.py
admin.site.register(Game)

Accessing the admin site will now give an AttributeError: 'OrderBy' object has no attribute 'startswith'

Variant 2 - Using the ModelAdmin ordering attribute:

//admin.py
class GameAdmin(models.ModelAdmin):
    ordering = [F("score").desc(nulls_last=True)]

runserver fails with error: TypeError: argument of type 'OrderBy' is not iterable

[Tim Graham]

It's a bug in a new feature in 2.0 (#28335).

[Mariusz Felisiak]

​PR

[GitHub <noreply@…>]

In c815213:

Fixed #28958 -- Fixed admin changelist crash when using a query expression in the page's ordering.

Thanks Tim Graham for the review.

[Mariusz Felisiak <felisiak.mariusz@…>]

In b54302d2:

[2.0.x] Fixed #28958 -- Fixed admin changelist crash when using a query expression in the page's ordering.

Thanks Tim Graham for the review.

Backport of c8152137400b5932578cd1788b79560c9772e56b from master

[GitHub <noreply@…>]

In 1d00923:

Refs #28958 -- Added a test for ModelAdmin with query expressions in ordering.

This provides additional test coverage but isn't a regression test for
the ticket's issue.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 8f67eea:

[2.0.x] Refs #28958 -- Added a test for ModelAdmin with query expressions in ordering.

This provides additional test coverage but isn't a regression test for
the ticket's issue.

Backport of 1d00923848d504c6132019492b8d5a6cdf8261db from master