===============
Getting Started
===============

Django-filter provides a simple way to filter down a queryset based on
parameters a user provides.  Say we have a ``Product`` model and we want to let
our users filter which products they see on a list page.

.. note::

    If you're using django-filter with Django Rest Framework, it's recommended
    that you read the :ref:`drf integration` docs after this guide.

The model
---------

Let's start with our model::

    from django.db import models

    class Product(models.Model):
        name = models.CharField(max_length=255)
        price = models.DecimalField(max_digits=5, decimal_places=2)
        description = models.TextField()
        release_date = models.DateField()
        manufacturer = models.ForeignKey(Manufacturer, on_delete=models.CASCADE)

The filter
----------

We have a number of fields and we want to let our users filter based on the
name, the price or the release_date.  We create a ``FilterSet`` for this::

    import django_filters

    class ProductFilter(django_filters.FilterSet):
        name = django_filters.CharFilter(lookup_expr='iexact')

        class Meta:
            model = Product
            fields = ['price', 'release_date']


As you can see this uses a very similar API to Django's ``ModelForm``.  Just
like with a ``ModelForm`` we can also override filters, or add new ones using a
declarative syntax.

Declaring filters
~~~~~~~~~~~~~~~~~

The declarative syntax provides you with the most flexibility when creating
filters, however it is fairly verbose. We'll use the below example to outline
the :ref:`core filter arguments <core-arguments>` on a ``FilterSet``::

    class ProductFilter(django_filters.FilterSet):
        price = django_filters.NumberFilter()
        price__gt = django_filters.NumberFilter(field_name='price', lookup_expr='gt')
        price__lt = django_filters.NumberFilter(field_name='price', lookup_expr='lt')

        release_year = django_filters.NumberFilter(field_name='release_date', lookup_expr='year')
        release_year__gt = django_filters.NumberFilter(field_name='release_date', lookup_expr='year__gt')
        release_year__lt = django_filters.NumberFilter(field_name='release_date', lookup_expr='year__lt')

        manufacturer__name = django_filters.CharFilter(lookup_expr='icontains')

        class Meta:
            model = Product
            fields = ['price', 'release_date', 'manufacturer']

There are two main arguments for filters:

- ``field_name``: The name of the model field to filter on. You can traverse
  "relationship paths" using Django's ``__`` syntax to filter fields on a
  related model. ex, ``manufacturer__name``.
- ``lookup_expr``: The `field lookup`_ to use when filtering. Django's ``__``
  syntax can again be used in order to support lookup transforms.
  ex, ``year__gte``.

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

Together, the field ``field_name`` and ``lookup_expr`` represent a complete Django
lookup expression. A detailed explanation of lookup expressions is provided in
Django's `lookup reference`_. django-filter supports expressions containing
both transforms and a final lookup.

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


Generating filters with Meta.fields
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The FilterSet Meta class provides a ``fields`` attribute that can be used for
easily specifying multiple filters without significant code duplication. The
base syntax supports a list of multiple field names::

    import django_filters

    class ProductFilter(django_filters.FilterSet):
        class Meta:
            model = Product
            fields = ['price', 'release_date']

The above generates 'exact' lookups for both the 'price' and 'release_date'
fields.

Additionally, a dictionary can be used to specify multiple lookup expressions
for each field::

    import django_filters

    class ProductFilter(django_filters.FilterSet):
        class Meta:
            model = Product
            fields = {
                'price': ['lt', 'gt'],
                'release_date': ['exact', 'year__gt'],
            }

The above would generate 'price__lt', 'price__gt', 'release_date', and
'release_date__year__gt' filters.

.. note::

    The filter lookup type 'exact' is an implicit default and therefore never
    added to a filter name. In the above example, the release date's exact
    filter is 'release_date', not 'release_date__exact'. This can be overridden
    by the FILTERS_DEFAULT_LOOKUP_EXPR setting.

Items in the ``fields`` sequence in the ``Meta`` class may include
"relationship paths" using Django's ``__`` syntax to filter on fields on a
related model::

    class ProductFilter(django_filters.FilterSet):
        class Meta:
            model = Product
            fields = ['manufacturer__country']


Overriding default filters
""""""""""""""""""""""""""

Like ``django.contrib.admin.ModelAdmin``, it is possible to override
default filters for all the models fields of the same kind using
``filter_overrides`` on the ``Meta`` class::

    class ProductFilter(django_filters.FilterSet):

        class Meta:
            model = Product
            fields = {
                'name': ['exact'],
                'release_date': ['isnull'],
            }
            filter_overrides = {
                models.CharField: {
                    'filter_class': django_filters.CharFilter,
                    'extra': lambda f: {
                        'lookup_expr': 'icontains',
                    },
                },
                models.BooleanField: {
                    'filter_class': django_filters.BooleanFilter,
                    'extra': lambda f: {
                        'widget': forms.CheckboxInput,
                    },
                },
            }


Request-based filtering
~~~~~~~~~~~~~~~~~~~~~~~

The ``FilterSet`` may be initialized with an optional ``request`` argument. If
a request object is passed, then you may access the request during filtering.
This allows you to filter by properties on the request, such as the currently
logged-in user or the ``Accepts-Languages`` header.

.. note::

    It is not guaranteed that a `request` will be provided to the `FilterSet`
    instance. Any code depending on a request should handle the `None` case.


Filtering the primary ``.qs``
"""""""""""""""""""""""""""""

To filter the primary queryset by the ``request`` object, simply override the
``FilterSet.qs`` property. For example, you could filter blog articles to only
those that are published and those that are owned by the logged-in user
(presumably the author's draft articles).

.. code-block:: python

    class ArticleFilter(django_filters.FilterSet):

        class Meta:
            model = Article
            fields = [...]

        @property
        def qs(self):
            parent = super().qs
            author = getattr(self.request, 'user', None)

            return parent.filter(is_published=True) \
                | parent.filter(author=author)


Filtering the related queryset for ``ModelChoiceFilter``
""""""""""""""""""""""""""""""""""""""""""""""""""""""""

The ``queryset`` argument for ``ModelChoiceFilter`` and ``ModelMultipleChoiceFilter``
supports callable behavior. If a callable is passed, it will be invoked with the
``request`` as its only argument. This allows you to perform the same kinds of
request-based filtering without resorting to overriding ``FilterSet.__init__``.

.. 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)
        ...


Customize filtering with ``Filter.method``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can control the behavior of a filter by specifying a ``method`` to perform
filtering. View more information in the :ref:`method reference <filter-method>`.
Note that you may access the filterset's properties, such as the ``request``.

.. code-block:: python

    class F(django_filters.FilterSet):
        username = CharFilter(method='my_custom_filter')

        class Meta:
            model = User
            fields = ['username']

        def my_custom_filter(self, queryset, name, value):
            return queryset.filter(**{
                name: value,
            })


The view
--------

Now we need to write a view::

    def product_list(request):
        f = ProductFilter(request.GET, queryset=Product.objects.all())
        return render(request, 'my_app/template.html', {'filter': f})

If a queryset argument isn't provided then all the items in the default manager
of the model will be used.

If you want to access the filtered objects in your views, for example if you
want to paginate them, you can do that. They are in f.qs


The URL conf
------------

We need a URL pattern to call the view::

    path('list/', views.product_list, name="product-list")


The template
------------

And lastly we need a template::

    {% extends "base.html" %}

    {% block content %}
        <form method="get">
            {{ filter.form.as_p }}
            <input type="submit" />
        </form>
        {% for obj in filter.qs %}
            {{ obj.name }} - ${{ obj.price }}<br />
        {% endfor %}
    {% endblock %}

And that's all there is to it!  The ``form`` attribute contains a normal
Django form, and when we iterate over the ``FilterSet.qs`` we get the objects in
the resulting queryset.


Generic view  & configuration
-----------------------------

In addition to the above usage there is also a class-based generic view
included in django-filter, which lives at ``django_filters.views.FilterView``.
You must provide either a ``model`` or ``filterset_class`` argument, similar to
``ListView`` in Django itself::

    # urls.py
    from django.urls import path
    from django_filters.views import FilterView
    from myapp.models import Product

    urlpatterns = [
        path("list/", FilterView.as_view(model=Product), name="product-list"),
    ]

If you provide a ``model`` optionally you can set ``filterset_fields`` to specify a list or a tuple of
the fields that you want to include for the automatic construction of the filterset class.

You must provide a template at ``<app>/<model>_filter.html`` which gets the
context parameter ``filter``.  Additionally, the context will contain
``object_list`` which holds the filtered queryset.

A legacy functional generic view is still included in django-filter, although
its use is deprecated.  It can be found at
``django_filters.views.object_filter``.  You must provide the same arguments
to it as the class based view::

    # urls.py
    from django.urls import path
    from django_filters.views import object_filter
    from myapp.models import Product

    urlpatterns = [
        path("list/", object_filter, {'model': Product}, name="product-list"),
    ]

The needed template and its context variables will also be the same as the
class-based view above.