ModelMultipleChoiceFilter with lookup_expr='in'

[emilt27]

We had the following field definition:

category = django_filters.ModelMultipleChoiceFilter(
    queryset=Category.objects.all(), 
    lookup_expr='in',
)

it worked correctly until last django-filter release. Now it's broken. Removing lookup_expr solves the issue, but It would be great to have more detailed message.

[rpkilby]

#1054 changed this. I don't think lookup_expr was previously used, and by default, Q objects are OR'ed together, so the result looks like it was performing an in lookup. e.g.,

MyModel.objects.filter(Q(field='value1') | Q(field='value2'))

The PR changed this so lookup expressions are accounted for, so you could queries like

MyModel.objects.filter(Q(field__contains='value1') | Q(field__contains='value2'))

However, in your case, the in lookup expects a list of values, which is why you get an error. It should be safe to drop lookup_expr='in'