Django Admin InputFilter

admin.py

# common/admin.py

class InputFilter(admin.SimpleListFilter):
    template = 'admin/input_filter.html'

    def lookups(self, request, model_admin):
        # Dummy, required to show the filter.
        return ((),)

    def choices(self, changelist):
        # Grab only the "all" option.
        all_choice = next(super().choices(changelist))
        all_choice['query_parts'] = (
            (k, v)
            for k, v in changelist.get_filters_params().items()
            if k != self.parameter_name
        )
        yield all_choice

input_filter.html

# common/templates/admin/input_filter.html

{% load i18n %}

<h3>{% blocktrans with filter_title=title %} By {{ filter_title }} {% endblocktrans %}</h3>
<ul>
    <li>
        {% with choices.0 as all_choice %}
        <form method="GET" action="">

            {% for k, v in all_choice.query_parts %}
            <input type="hidden" name="{{ k }}" value="{{ v }}" />
            {% endfor %}

            <input  type="text"
                    value="{{ spec.value|default_if_none:'' }}"
                    name="{{ spec.parameter_name }}"/>

            {% if not all_choice.selected %}
                <strong><a href="{{ all_choice.query_string }}">x {% trans 'Remove' %}</a></strong>
            {% endif %}

        </form>
        {% endwith %}
    </li>
</ul>

In Django 5 admin filters now handle multi-valued query parameters.

Django 5 compatible version:

class InputFilter(SimpleListFilter):
    template = 'admin/input_filter.html'

    def lookups(self, request, model_admin):
        # Dummy, required to show the filter.
        return ((),)

    def choices(self, changelist):
        # Grab only the "all" option.
        all_choice = next(super().choices(changelist))
        all_choice['query_parts'] = (
            (k, v)
            for k, values in changelist.get_filters_params().items()
            for v in values
            if k != self.parameter_name
        )
        yield all_choice

This will only have any effect if the user edited the URL, right?