================
Filter Reference
================

This is a reference document with a list of the filters and their arguments.

.. _core-arguments:

Core Arguments
--------------

The following are the core arguments that apply to all filters. Note that they
are joined to construct the complete `lookup expression`_ that is the left hand
side of the ORM ``.filter()`` call.

.. _`lookup expression`: https://docs.djangoproject.com/en/stable/ref/models/lookups/#module-django.db.models.lookups

``field_name``
~~~~~~~~~~~~~~

The name of the model field that is filtered against. If this argument is not
provided, it defaults the filter's attribute name on the ``FilterSet`` class.
Field names can traverse relationships by joining the related parts with the ORM
lookup separator (``__``). e.g., a product's ``manufacturer__name``.

``lookup_expr``
~~~~~~~~~~~~~~~

The `field lookup`_ that should be performed in the filter call. Defaults to
``exact``. The ``lookup_expr`` can contain transforms if the expression parts
are joined by the ORM lookup separator (``__``). e.g., filter a datetime by its
year part ``year__gt``.

.. _`Field lookup`: https://docs.djangoproject.com/en/stable/ref/models/querysets/#field-lookups

.. _keyword-only-arguments:

Keyword-only Arguments
----------------------

The following are optional arguments that can be used to modify the behavior of
all filters.

``label``
~~~~~~~~~

The label as it will appear in the HTML, analogous to a form field's label
argument. If a label is not provided, a verbose label will be generated based
on the field ``field_name`` and the parts of the ``lookup_expr``
(see: :ref:`verbose-lookups-setting`).

.. _filter-method:

``method``
~~~~~~~~~~

An optional argument that tells the filter how to handle the queryset. It can
accept either a callable or the name of a method on the ``FilterSet``. The
callable receives a ``QuerySet``, the name of the model field to filter on, and
the value to filter with. It should return a filtered ``Queryset``.

Note that the value is validated by the ``Filter.field``, so raw value
transformation and empty value checking should be unnecessary.

.. code-block:: python

    class F(FilterSet):
        """Filter for Books by if books are published or not"""
        published = BooleanFilter(field_name='published_on', method='filter_published')

        def filter_published(self, queryset, name, value):
            # construct the full lookup expression.
            lookup = '__'.join([name, 'isnull'])
            return queryset.filter(**{lookup: False})

            # alternatively, you could opt to hardcode the lookup. e.g.,
            # return queryset.filter(published_on__isnull=False)

        class Meta:
            model = Book
            fields = ['published']


    # Callables may also be defined out of the class scope.
    def filter_not_empty(queryset, name, value):
        lookup = '__'.join([name, 'isnull'])
        return queryset.filter(**{lookup: False})

    class F(FilterSet):
        """Filter for Books by if books are published or not"""
        published = BooleanFilter(field_name='published_on', method=filter_not_empty)

        class Meta:
            model = Book
            fields = ['published']


``distinct``
~~~~~~~~~~~~

A boolean that specifies whether the Filter will use distinct on the queryset.
This option can be used to eliminate duplicate results when using filters that
span relationships. Defaults to ``False``.

``exclude``
~~~~~~~~~~~

A boolean that specifies whether the Filter should use ``filter`` or ``exclude``
on the queryset. Defaults to ``False``.

``required``
~~~~~~~~~~~~

A boolean that specifies whether the Filter is required or not. Defaults to ``False``.


``**kwargs``
~~~~~~~~~~~~

Any additional keyword arguments are stored as the ``extra`` parameter on the
filter. They are provided to the accompanying form ``Field`` and can be used to
provide arguments like ``choices``. Some field-related arguments:

``widget``
""""""""""

The django.form Widget class which will represent the ``Filter``.  In addition
to the widgets that are included with Django that you can use there are
additional ones that django-filter provides which may be useful:

    * :ref:`LinkWidget <link-widget>` -- this displays the options in a manner
      similar to the way the Django Admin does, as a series of links. The link
      for the selected option will have ``class="selected"``.
    * :ref:`BooleanWidget <boolean-widget>` -- this widget converts its input
      into Python's True/False values. It will convert all case variations of
      ``True`` and ``False`` into the internal Python values.
    * :ref:`CSVWidget <csv-widget>` -- this widget expects a comma separated
      value and converts it into a list of string values. It is expected that
      the field class handle a list of values as well as type conversion.
    * :ref:`RangeWidget <range-widget>` -- this widget is used with ``RangeFilter``
      to generate two form input elements using a single field.


ModelChoiceFilter and ModelMultipleChoiceFilter arguments
---------------------------------------------------------

These arguments apply specifically to ModelChoiceFilter and
ModelMultipleChoiceFilter only.

``queryset``
~~~~~~~~~~~~

``ModelChoiceFilter`` and ``ModelMultipleChoiceFilter`` require a queryset to
operate on which must be passed as a kwarg.

``to_field_name``
~~~~~~~~~~~~~~~~~

If you pass in ``to_field_name`` (which gets forwarded to the Django field),
it will be used also in the default ``get_filter_predicate`` implementation
as the model's attribute.


Filters
-------

``CharFilter``
~~~~~~~~~~~~~~

This filter does simple character matches, used with ``CharField`` and
``TextField`` by default.

``UUIDFilter``
~~~~~~~~~~~~~~

This filter matches UUID values, used with ``models.UUIDField`` by default.

``BooleanFilter``
~~~~~~~~~~~~~~~~~

This filter matches a boolean, either ``True`` or ``False``, used with
``BooleanField`` and ``NullBooleanField`` by default.

.. _choice-filter:

``ChoiceFilter``
~~~~~~~~~~~~~~~~

This filter matches values in its ``choices`` argument. The ``choices`` must be
explicitly passed when the filter is declared on the ``FilterSet``. For example,

.. code-block:: python

    class User(models.Model):
        username = models.CharField(max_length=255)
        first_name = SubCharField(max_length=100)
        last_name = SubSubCharField(max_length=100)

        status = models.IntegerField(choices=STATUS_CHOICES, default=0)

    STATUS_CHOICES = (
        (0, 'Regular'),
        (1, 'Manager'),
        (2, 'Admin'),
    )

    class F(FilterSet):
        status = ChoiceFilter(choices=STATUS_CHOICES)
        class Meta:
            model = User
            fields = ['status']


``ChoiceFilter`` also has arguments that enable a choice for not filtering, as
well as a choice for filtering by ``None`` values. Each of the arguments have a
corresponding global setting (:doc:`/ref/settings`).

* ``empty_label``: The display label to use for the select choice to not filter.
  The choice may be disabled by setting this argument to ``None``. Defaults to
  ``FILTERS_EMPTY_CHOICE_LABEL``.
* ``null_label``: The display label to use for the choice to filter by ``None``
  values. The choice may be disabled by setting this argument to ``None``.
  Defaults to ``FILTERS_NULL_CHOICE_LABEL``.
* ``null_value``: The special value to match to enable filtering by ``None``
  values. This value defaults ``FILTERS_NULL_CHOICE_VALUE`` and needs to be
  a non-empty value (``''``, ``None``, ``[]``, ``()``, ``{}``).


``TypedChoiceFilter``
~~~~~~~~~~~~~~~~~~~~~

The same as ``ChoiceFilter`` with the added possibility to convert value to
match against. This could be done by using `coerce` parameter.
An example use-case is limiting boolean choices to match against so only
some predefined strings could be used as input of a boolean filter::

    import django_filters
    from distutils.util import strtobool

    BOOLEAN_CHOICES = (('false', 'False'), ('true', 'True'),)

    class YourFilterSet(django_filters.FilterSet):
        ...
        flag = django_filters.TypedChoiceFilter(choices=BOOLEAN_CHOICES,
                                                coerce=strtobool)


``MultipleChoiceFilter``
~~~~~~~~~~~~~~~~~~~~~~~~

The same as ``ChoiceFilter`` except the user can select multiple choices
and the filter will form the OR of these choices by default to match items.
The filter will form the AND of the selected choices when the ``conjoined=True``
argument is passed to this class.

Multiple choices are represented in the query string by reusing the same key with
different values (e.g. ''?status=Regular&status=Admin'').

``distinct`` defaults to ``True`` as to-many relationships will generally require this.

Advanced Use: Depending on your application logic, when all or no choices are
selected, filtering may be a noop. In this case you may wish to avoid the
filtering overhead, particularly of the `distinct` call.

Set `always_filter` to False after instantiation to enable the default `is_noop`
test.

Override `is_noop` if you require a different test for your application.


``TypedMultipleChoiceFilter``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Like ``MultipleChoiceFilter``, but in addition accepts the ``coerce`` parameter, as
in ``TypedChoiceFilter``.


``DateFilter``
~~~~~~~~~~~~~~

Matches on a date.  Used with ``DateField`` by default.


``TimeFilter``
~~~~~~~~~~~~~~

Matches on a time.  Used with ``TimeField`` by default.


``DateTimeFilter``
~~~~~~~~~~~~~~~~~~

Matches on a date and time.  Used with ``DateTimeField`` by default.


``IsoDateTimeFilter``
~~~~~~~~~~~~~~~~~~~~~

Uses ``IsoDateTimeField`` to support filtering on ISO 8601 formatted dates, as are often
used in APIs, and are employed by default by Django REST Framework.

Example::

    class F(FilterSet):
        """Filter for Books by date published, using ISO 8601 formatted dates"""
        published = IsoDateTimeFilter()

        class Meta:
            model = Book
            fields = ['published']


``DurationFilter``
~~~~~~~~~~~~~~~~~~

Matches on a duration.  Used with ``DurationField`` by default.

Supports both Django ('%d %H:%M:%S.%f') and ISO 8601 formatted durations (but
only the sections that are accepted by Python's timedelta, so no year, month,
and week designators, e.g. 'P3DT10H22M').


``ModelChoiceFilter``
~~~~~~~~~~~~~~~~~~~~~

Similar to a ``ChoiceFilter`` except it works with related models, used for
``ForeignKey`` by default.

If automatically instantiated, ``ModelChoiceFilter`` will use the default
``QuerySet`` for the related field. If manually instantiated you **must**
provide the ``queryset`` kwarg.

Example::

    class F(FilterSet):
        """Filter for books by author"""
        author = ModelChoiceFilter(queryset=Author.objects.all())

        class Meta:
            model = Book
            fields = ['author']

The ``queryset`` argument also supports callable behavior. If a callable is
passed, it will be invoked with ``Filterset.request`` as its only argument.
This allows you to easily filter by properties on the request object without
having to override the ``FilterSet.__init__``.

.. note::

    You should expect that the `request` object may be `None`.

.. code-block:: python

    def departments(request):
        if request is None:
            return Department.objects.none()

        company = request.user.company
        return company.department_set.all()

    class EmployeeFilter(filters.FilterSet):
        department = filters.ModelChoiceFilter(queryset=departments)
        ...


``ModelMultipleChoiceFilter``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Similar to a ``MultipleChoiceFilter`` except it works with related models, used
for ``ManyToManyField`` by default.

As with ``ModelChoiceFilter``, if automatically instantiated,
``ModelMultipleChoiceFilter`` will use the default ``QuerySet`` for the related
field. If manually instantiated you **must** provide the ``queryset`` kwarg.
Like ``ModelChoiceFilter``, the ``queryset`` argument has callable behavior.

To use a custom field name for the lookup, you can use ``to_field_name``::

    class FooFilter(BaseFilterSet):
        foo = django_filters.filters.ModelMultipleChoiceFilter(
            field_name='attr__uuid',
            to_field_name='uuid',
            queryset=Foo.objects.all(),
        )

If you want to use a custom queryset, e.g. to add annotated fields, this can be
done as follows::

    class MyMultipleChoiceFilter(django_filters.ModelMultipleChoiceFilter):
        def get_filter_predicate(self, v):
            return {'annotated_field': v.annotated_field}

        def filter(self, qs, value):
            if value:
                qs = qs.annotate_with_custom_field()
                qs = super().filter(qs, value)
            return qs

    foo = MyMultipleChoiceFilter(
        to_field_name='annotated_field',
        queryset=Model.objects.annotate_with_custom_field(),
    )

The ``annotate_with_custom_field`` method would be defined through a custom
QuerySet, which then gets used as the model's manager::

    class CustomQuerySet(models.QuerySet):
        def annotate_with_custom_field(self):
            return self.annotate(
                custom_field=Case(
                    When(foo__isnull=False,
                         then=F('foo__uuid')),
                    When(bar__isnull=False,
                         then=F('bar__uuid')),
                    default=None,
                ),
            )

    class MyModel(models.Model):
        objects = CustomQuerySet.as_manager()


``NumberFilter``
~~~~~~~~~~~~~~~~

Filters based on a numerical value, used with ``IntegerField``, ``FloatField``,
and ``DecimalField`` by default.

.. method:: NumberFilter.get_max_validator()

    Return a ``MaxValueValidator`` instance that will be added to
    ``field.validators``. By default uses a limit value of ``1e50``. Return
    ``None`` to disable maximum value validation.

``NumericRangeFilter``
~~~~~~~~~~~~~~~~~~~~~~

Filters where a value is between two numerical values, or greater than a minimum or less
than a maximum where only one limit value is provided. This filter is designed to work
with the Postgres Numerical Range Fields, including ``IntegerRangeField``,
``BigIntegerRangeField`` and ``FloatRangeField`` (available since Django 1.8). The default
widget used is the ``RangeField``.

Regular field lookups are available in addition to several containment lookups, including
``overlap``, ``contains``, and ``contained_by``. More details in the Django `docs`__.

__ https://docs.djangoproject.com/en/stable/ref/contrib/postgres/fields/#querying-range-fields

If the lower limit value is provided, the filter automatically defaults to ``startswith``
as the lookup and ``endswith`` if only the upper limit value is provided.

``RangeFilter``
~~~~~~~~~~~~~~~

Filters where a value is between two numerical values, or greater than a minimum or less than a maximum where only one limit value is provided. ::

    class F(FilterSet):
        """Filter for Books by Price"""
        price = RangeFilter()

        class Meta:
            model = Book
            fields = ['price']

    qs = Book.objects.all().order_by('title')

    # Range: Books between 5€ and 15€
    f = F({'price_min': '5', 'price_max': '15'}, queryset=qs)

    # Min-Only: Books costing more the 11€
    f = F({'price_min': '11'}, queryset=qs)

    # Max-Only: Books costing less than 19€
    f = F({'price_max': '19'}, queryset=qs)


``DateRangeFilter``
~~~~~~~~~~~~~~~~~~~

Filter similar to the admin changelist date one, it has a number of common
selections for working with date fields.

``DateFromToRangeFilter``
~~~~~~~~~~~~~~~~~~~~~~~~~

Similar to a ``RangeFilter`` except it uses dates instead of numerical values. It can be used with ``DateField``. It also works with ``DateTimeField``, but takes into consideration only the date.

Example of using the ``DateField`` field::

    class Comment(models.Model):
        date = models.DateField()
        time = models.TimeField()

    class F(FilterSet):
        date = DateFromToRangeFilter()

        class Meta:
            model = Comment
            fields = ['date']

    # Range: Comments added between 2016-01-01 and 2016-02-01
    f = F({'date_after': '2016-01-01', 'date_before': '2016-02-01'})

    # Min-Only: Comments added after 2016-01-01
    f = F({'date_after': '2016-01-01'})

    # Max-Only: Comments added before 2016-02-01
    f = F({'date_before': '2016-02-01'})

.. note::
    When filtering ranges that occurs on DST transition dates ``DateFromToRangeFilter`` will use the first valid hour of the day for start datetime and the last valid hour of the day for end datetime.
    This is OK for most applications, but if you want to customize this behavior you must extend ``DateFromToRangeFilter`` and make a custom field for it.

.. warning::
    If you're using Django prior to 1.9 you may hit ``AmbiguousTimeError`` or ``NonExistentTimeError`` when start/end date matches DST start/end respectively.
    This occurs because versions before 1.9 don't allow to change the DST behavior for making a datetime aware.

Example of using the ``DateTimeField`` field::

    class Article(models.Model):
        published = models.DateTimeField()

    class F(FilterSet):
        published = DateFromToRangeFilter()

        class Meta:
            model = Article
            fields = ['published']

    Article.objects.create(published='2016-01-01 8:00')
    Article.objects.create(published='2016-01-20 10:00')
    Article.objects.create(published='2016-02-10 12:00')

    # Range: Articles published between 2016-01-01 and 2016-02-01
    f = F({'published_after': '2016-01-01', 'published_before': '2016-02-01'})
    assert len(f.qs) == 2

    # Min-Only: Articles published after 2016-01-01
    f = F({'published_after': '2016-01-01'})
    assert len(f.qs) == 3

    # Max-Only: Articles published before 2016-02-01
    f = F({'published_before': '2016-02-01'})
    assert len(f.qs) == 2

``DateTimeFromToRangeFilter``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Similar to a ``RangeFilter`` except it uses datetime format values instead of numerical values. It can be used with ``DateTimeField``.

Example::

    class Article(models.Model):
        published = models.DateTimeField()

    class F(FilterSet):
        published = DateTimeFromToRangeFilter()

        class Meta:
            model = Article
            fields = ['published']

    Article.objects.create(published='2016-01-01 8:00')
    Article.objects.create(published='2016-01-01 9:30')
    Article.objects.create(published='2016-01-02 8:00')

    # Range: Articles published 2016-01-01 between 8:00 and 10:00
    f = F({'published_after': '2016-01-01 8:00', 'published_before': '2016-01-01 10:00'})
    assert len(f.qs) == 2

    # Min-Only: Articles published after 2016-01-01 8:00
    f = F({'published_after': '2016-01-01 8:00'})
    assert len(f.qs) == 3

    # Max-Only: Articles published before 2016-01-01 10:00
    f = F({'published_before': '2016-01-01 10:00'})
    assert len(f.qs) == 2

``IsoDateTimeFromToRangeFilter``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Similar to a ``RangeFilter`` except it uses ISO 8601 formatted values instead of numerical values. It can be used with ``IsoDateTimeField``.

Example::

    class Article(models.Model):
        published = django_filters.IsoDateTimeField()

    class F(FilterSet):
        published = IsoDateTimeFromToRangeFilter()

        class Meta:
            model = Article
            fields = ['published']

    Article.objects.create(published='2016-01-01T8:00:00+01:00')
    Article.objects.create(published='2016-01-01T9:30:00+01:00')
    Article.objects.create(published='2016-01-02T8:00:00+01:00')

    # Range: Articles published 2016-01-01 between 8:00 and 10:00
    f = F({'published_after': '2016-01-01T8:00:00+01:00', 'published_before': '2016-01-01T10:00:00+01:00'})
    assert len(f.qs) == 2

    # Min-Only: Articles published after 2016-01-01 8:00
    f = F({'published_after': '2016-01-01T8:00:00+01:00'})
    assert len(f.qs) == 3

    # Max-Only: Articles published before 2016-01-01 10:00
    f = F({'published_before': '2016-01-01T10:00:00+0100'})
    assert len(f.qs) == 2

``TimeRangeFilter``
~~~~~~~~~~~~~~~~~~~

Similar to a ``RangeFilter`` except it uses time format values instead of numerical values. It can be used with ``TimeField``.

Example::

    class Comment(models.Model):
        date = models.DateField()
        time = models.TimeField()

    class F(FilterSet):
        time = TimeRangeFilter()

        class Meta:
            model = Comment
            fields = ['time']

    # Range: Comments added between 8:00 and 10:00
    f = F({'time_after': '8:00', 'time_before': '10:00'})

    # Min-Only: Comments added after 8:00
    f = F({'time_after': '8:00'})

    # Max-Only: Comments added before 10:00
    f = F({'time_before': '10:00'})

``AllValuesFilter``
~~~~~~~~~~~~~~~~~~~

This is a ``ChoiceFilter`` whose choices are the current values in the
database.  So if in the DB for the given field you have values of 5, 7, and 9
each of those is present as an option.  This is similar to the default behavior
of the admin.

``AllValuesMultipleFilter``
~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is a ``MultipleChoiceFilter`` whose choices are the current values in the
database.  So if in the DB for the given field you have values of 5, 7, and 9
each of those is present as an option.  This is similar to the default behavior
of the admin.

.. _lookup-choice-filter:

``LookupChoiceFilter``
~~~~~~~~~~~~~~~~~~~~~~

A combined filter that allows users to select the lookup expression from a dropdown.

* ``lookup_choices`` is an optional argument that accepts multiple input
  formats, and is ultimately normalized as the choices used in the lookup
  dropdown. See ``.get_lookup_choices()`` for more information.

* ``field_class`` is an optional argument that allows you to set the inner
  form field class used to validate the value. Default: ``forms.CharField``

ex::

    price = django_filters.LookupChoiceFilter(
        field_class=forms.DecimalField,
        lookup_choices=[
            ('exact', 'Equals'),
            ('gt', 'Greater than'),
            ('lt', 'Less than'),
        ]
    )

.. _base-in-filter:

``BaseInFilter``
~~~~~~~~~~~~~~~~

This is a base class used for creating IN lookup filters. It is expected that
this filter class is used in conjunction with another filter class, as this
class **only** validates that the incoming value is comma-separated. The secondary
filter is then used to validate the individual values.

Example::

    class NumberInFilter(BaseInFilter, NumberFilter):
        pass

    class F(FilterSet):
        id__in = NumberInFilter(field_name='id', lookup_expr='in')

        class Meta:
            model = User

    User.objects.create(username='alex')
    User.objects.create(username='jacob')
    User.objects.create(username='aaron')
    User.objects.create(username='carl')

    # In: User with IDs 1 and 3.
    f = F({'id__in': '1,3'})
    assert len(f.qs) == 2

``BaseRangeFilter``
~~~~~~~~~~~~~~~~~~~

This is a base class used for creating RANGE lookup filters. It behaves
identically to ``BaseInFilter`` with the exception that it expects only two
comma-separated values.

Example::

    class NumberRangeFilter(BaseRangeFilter, NumberFilter):
        pass

    class F(FilterSet):
        id__range = NumberRangeFilter(field_name='id', lookup_expr='range')

        class Meta:
            model = User

    User.objects.create(username='alex')
    User.objects.create(username='jacob')
    User.objects.create(username='aaron')
    User.objects.create(username='carl')

    # Range: User with IDs between 1 and 3.
    f = F({'id__range': '1,3'})
    assert len(f.qs) == 3


.. _ordering-filter:

``OrderingFilter``
~~~~~~~~~~~~~~~~~~

Enable queryset ordering. As an extension of ``ChoiceFilter`` it accepts
two additional arguments that are used to build the ordering choices.

* ``fields`` is a mapping of {model field name: parameter name}. The
  parameter names are exposed in the choices and mask/alias the field
  names used in the ``order_by()`` call. Similar to field ``choices``,
  ``fields`` accepts the 'list of two-tuples' syntax that retains order.
  ``fields`` may also just be an iterable of strings. In this case, the
  field names simply double as the exposed parameter names.

* ``field_labels`` is an optional argument that allows you to customize
  the display label for the corresponding parameter. It accepts a mapping
  of {field name: human readable label}. Keep in mind that the key is the
  field name, and not the exposed parameter name.

.. code-block:: python

    class UserFilter(FilterSet):
        account = CharFilter(field_name='username')
        status = NumberFilter(field_name='status')

        o = OrderingFilter(
            # tuple-mapping retains order
            fields=(
                ('username', 'account'),
                ('first_name', 'first_name'),
                ('last_name', 'last_name'),
            ),

            # labels do not need to retain order
            field_labels={
                'username': 'User account',
            }
        )

        class Meta:
            model = User
            fields = ['first_name', 'last_name']

    >>> UserFilter().filters['o'].field.choices
    [
        ('account', 'User account'),
        ('-account', 'User account (descending)'),
        ('first_name', 'First name'),
        ('-first_name', 'First name (descending)'),
        ('last_name', 'Last name'),
        ('-last_name', 'Last name (descending)'),
    ]

Additionally, you can just provide your own ``choices`` if you require
explicit control over the exposed options. For example, when you might
want to disable descending sort options.

.. code-block:: python

    class UserFilter(FilterSet):
        account = CharFilter(field_name='username')
        status = NumberFilter(field_name='status')

        o = OrderingFilter(
            choices=(
                ('account', 'Account'),
            ),
            fields={
                'username': 'account',
            },
        )

This filter is also CSV-based, and accepts multiple ordering params. The
default select widget does not enable the use of this, but it is useful
for APIs. ``SelectMultiple`` widgets are not compatible, given that they
are not able to retain selection order.

Adding Custom filter choices
""""""""""""""""""""""""""""

If you wish to sort by non-model fields, you'll need to add custom handling to an
``OrderingFilter`` subclass. For example, if you want to sort by a computed
'relevance' factor, you would need to do something like the following:

.. code-block:: python

    class CustomOrderingFilter(django_filters.OrderingFilter):

        def __init__(self, *args, **kwargs):
            super().__init__(*args, **kwargs)
            self.extra['choices'] += [
                ('relevance', 'Relevance'),
                ('-relevance', 'Relevance (descending)'),
            ]


        def filter(self, qs, value):
            # OrderingFilter is CSV-based, so `value` is a list
            if any(v in ['relevance', '-relevance'] for v in value):
                # sort queryset by relevance
                return ...

            return super().filter(qs, value)
