An easy way to exclude

[smartlegionlab]

Hello, is there any easy way to exclude?

For example, there is a filter in which there are a lot of city names.

For filtering, I can choose the ones I need, but what if I need all but one? All that comes to mind is to add a second similar filter below with exclude=True, but what if I have very large forms, duplicating filters to add the possibility of exclusion is clearly not an option?

This approach is clearly redundant and wrong. But I couldn't find anything in the official documentation:

class ClientFilterSet(django_filters.FilterSet):
    class Meta:
        model = Client
        fields = []

    city = django_filters.ModelMultipleChoiceFilter(
        field_name="city", lookup_expr='exact', label=_('City'),
        widget=SelectMultiple(attrs={'class': 'chosen-select'}),
        queryset=SiteGtd.objects.filter(type='city'))

    exc_city = django_filters.ModelMultipleChoiceFilter(
        field_name="city", lookup_expr='exact', label=_('City'), exclude=True,
        widget=SelectMultiple(attrs={'class': 'chosen-select'}),
        queryset=SiteGtd.objects.filter(type='city'))

The second thing that comes to mind is to use some kind of "Select All" method. In order to remove unnecessary options after choosing with one team.

[aidanlister]

I really want this too, #978 and see this discussion about it, #1484

[rodrigondec]

As per @carltongibson mentioned here it's possible with some extensions and overwriting.

FilterSet code

from django_filters import FilterSet
from django_filters.conf import settings
from django_filters.filterset import resolve_field


class AutomaticallyExcludeFilterSet(FilterSet):
    @classmethod
    def get_filter_name(cls, field_name, lookup_expr):
        if lookup_expr[0] == "!":
            lookup_expr = lookup_expr[1:]
            suffix = "!"
        else:
            suffix = ""
        field_name = super().get_filter_name(field_name, lookup_expr)
        return f"{field_name}{suffix}"

    @classmethod
    def filter_for_field(cls, field, field_name, lookup_expr=None):
        if lookup_expr is None:
            lookup_expr = settings.DEFAULT_LOOKUP_EXPR

        if lookup_expr[0] == "!":
            lookup_expr = lookup_expr[1:]
            exclude = True
        else:
            exclude = False

        field, lookup_type = resolve_field(field, lookup_expr)

        default = {
            "field_name": field_name,
            "lookup_expr": lookup_expr,
            "exclude": exclude,
        }

        filter_class, params = cls.filter_for_lookup(field, lookup_type)
        default.update(params)

        assert filter_class is not None, (
            "%s resolved field '%s' with '%s' lookup to an unrecognized field "
            "type %s. Try adding an override to 'Meta.filter_overrides'. See: "
            "https://django-filter.readthedocs.io/en/main/ref/filterset.html"
            "#customise-filter-generation-with-filter-overrides"
        ) % (cls.__name__, field_name, lookup_expr, field.__class__.__name__)

        return filter_class(**default)

backend code

from django_filters.rest_framework.backends import DjangoFilterBackend


class AutomaticallyExcludeDjangoFilterBackend(DjangoFilterBackend):
    filterset_base = AutomaticallyExcludeFilterSet