Annotation with `Case` can't be used with `exclude`

[Ram Rachum]

When you define an annotation that uses Case, you can use .filter on it but you can't use .exclude. (You get various exceptions about .null and .get_col not existing.)

Example:

def my_view(request, *args, **kwargs):
    things = models.Thing.objects.all().annotate(
        bar=django.db.models.Case(
            django.db.models.When(
                foo='foo',
                then=django.db.models.Value('bar')
            ),
            default=django.db.models.Value('baz'),
            output_field=django.db.models.CharField()
        )
    )
    
    print(things.filter(bar='bar')) # This one works
    print(things.exclude(bar='bar')) # This one doesn't 
    return django.http.HttpResponse(str(things))

Full working example attached to this ticket. (Simply run migrate, then runserver, then access the root URL to see the Django debug page for the exception.)

[Ram Rachum]

Full working example, run migrate then runserver then access root url to see the exception

[Tim Graham]

Adding a regression test for 1.8. It seems this was fixed in master by b68212f539f206679580afbfd008e7d329c9cd31.

[Simon Charette]

Added regression test LGTM.

[Tim Graham]

I think we should try to fix the problem on 1.8 since it's a crashing bug in a new feature.

[Ram Rachum]

I agree with Tim, for what it's worth.

[Andriy Sokolovskiy]

Talked with Anssi, going to fix that

[Andriy Sokolovskiy]

​https://github.com/django/django/pull/4794

[Andriy Sokolovskiy]

Related PR - ​https://github.com/django/django/pull/4795

[Tim Graham <timograham@…>]

In 469f1e3:

[1.8.x] Fixed #24833 -- Fixed Case expressions with exclude().

[Tim Graham <timograham@…>]

In 286d0e6a:

Refs #24833 -- Forwardported some of "Fixed Case expressions with exclude()."

Partial forwardport of 469f1e362bb9670b174b37da9edd4631aff7badb from stable/1.8.x
as the issue was already fixed in master.