====================
Integration with DRF
====================

Integration with `Django Rest Framework`__ is provided through a DRF-specific ``FilterSet`` and a `filter backend`__. These may be found in the ``rest_framework`` sub-package.

__ http://www.django-rest-framework.org/
__ http://www.django-rest-framework.org/api-guide/filtering/


Quickstart
----------

Using the new ``FilterSet`` simply requires changing the import path. Instead of importing from ``django_filters``, import from the ``rest_framework`` sub-package.

.. code-block:: python

    from django_filters import rest_framework as filters

    class ProductFilter(filters.FilterSet):
        ...

Your view class will also need to add ``DjangoFilterBackend`` to the ``filter_backends``.

.. code-block:: python

    from django_filters import rest_framework as filters

    class ProductList(generics.ListAPIView):
        queryset = Product.objects.all()
        serializer_class = ProductSerializer
        filter_backends = (filters.DjangoFilterBackend,)
        filterset_fields = ('category', 'in_stock')

If you want to use the django-filter backend by default, add it to the ``DEFAULT_FILTER_BACKENDS`` setting.

.. code-block:: python

    # settings.py
    INSTALLED_APPS = [
        ...
        'rest_framework',
        'django_filters',
    ]

    REST_FRAMEWORK = {
        'DEFAULT_FILTER_BACKENDS': (
            'django_filters.rest_framework.DjangoFilterBackend',
            ...
        ),
    }


Adding a FilterSet with ``filterset_class``
-------------------------------------------

To enable filtering with a ``FilterSet``, add it to the ``filterset_class`` parameter on your view class.

.. code-block:: python

    from rest_framework import generics
    from django_filters import rest_framework as filters
    from myapp import Product


    class ProductFilter(filters.FilterSet):
        min_price = filters.NumberFilter(field_name="price", lookup_expr='gte')
        max_price = filters.NumberFilter(field_name="price", lookup_expr='lte')

        class Meta:
            model = Product
            fields = ['category', 'in_stock', 'min_price', 'max_price']


    class ProductList(generics.ListAPIView):
        queryset = Product.objects.all()
        serializer_class = ProductSerializer
        filter_backends = (filters.DjangoFilterBackend,)
        filterset_class = ProductFilter


Using the ``filterset_fields`` shortcut
---------------------------------------

You may bypass creating a ``FilterSet`` by instead adding ``filterset_fields`` to your view class. This is equivalent to creating a FilterSet with just :ref:`Meta.fields <fields>`.


.. code-block:: python

    from rest_framework import generics
    from django_filters import rest_framework as filters
    from myapp import Product


    class ProductList(generics.ListAPIView):
        queryset = Product.objects.all()
        filter_backends = (filters.DjangoFilterBackend,)
        filterset_fields = ('category', 'in_stock')


    # Equivalent FilterSet:
    class ProductFilter(filters.FilterSet):
        class Meta:
            model = Product
            fields = ('category', 'in_stock')


Note that using ``filterset_fields`` and ``filterset_class`` together is not
supported.


Overriding FilterSet creation
-----------------------------

``FilterSet`` creation can be customized by overriding the following methods on the backend class:

* ``.get_filterset(self, request, queryset, view)``
* ``.get_filterset_class(self, view, queryset=None)``
* ``.get_filterset_kwargs(self, request, queryset, view)``

You can override these methods on a case-by-case basis for each view, creating unique backends, or these methods can be used to write your own hooks to the view class.

.. code-block:: python

    class MyFilterBackend(filters.DjangoFilterBackend):
        def get_filterset_kwargs(self, request, queryset, view):
            kwargs = super().get_filterset_kwargs(request, queryset, view)

            # merge filterset kwargs provided by view class
            if hasattr(view, 'get_filterset_kwargs'):
                kwargs.update(view.get_filterset_kwargs())

            return kwargs


    class BookFilter(filters.FilterSet):
        def __init__(self, *args, author=None, **kwargs):
            super().__init__(*args, **kwargs)
            # do something w/ author


    class BookViewSet(viewsets.ModelViewSet):
        filter_backends = [MyFilterBackend]
        filterset_class = BookFilter

        def get_filterset_kwargs(self):
            return {
                'author': self.get_author(),
            }

Schema Generation with Core API and Open API
--------------------------------------------

The backend class integrates with DRF's schema generation by implementing ``get_schema_fields()`` and ``get_schema_operation_parameters()``. ``get_schema_fields()`` is automatically enabled when Core API is installed. ``get_schema_operation_parameters()`` is always enabled for Open API (new since DRF 3.9). Schema generation usually functions seamlessly, however the implementation does expect to invoke the view's ``get_queryset()`` method. There is a caveat in that views are artificially constructed during schema generation, so the ``args`` and ``kwargs`` attributes will be empty. If you depend on arguments parsed from the URL, you will need to handle their absence in ``get_queryset()``.

For example, your get queryset method may look like this:

.. code-block:: python

    class IssueViewSet(views.ModelViewSet):
        queryset = models.Issue.objects.all()

        def get_project(self):
            return models.Project.objects.get(pk=self.kwargs['project_id'])

        def get_queryset(self):
            project = self.get_project()

            return self.queryset \
                .filter(project=project) \
                .filter(author=self.request.user)

This could be rewritten like so:

.. code-block:: python

    class IssueViewSet(views.ModelViewSet):
        queryset = models.Issue.objects.all()

        def get_project(self):
            try:
                return models.Project.objects.get(pk=self.kwargs['project_id'])
            except models.Project.DoesNotExist:
                return None

        def get_queryset(self):
            project = self.get_project()

            if project is None:
                return self.queryset.none()

            return self.queryset \
                .filter(project=project) \
                .filter(author=self.request.user)

Or more simply as:

.. code-block:: python

    class IssueViewSet(views.ModelViewSet):
        queryset = models.Issue.objects.all()

        def get_queryset(self):
            # project_id may be None
            return self.queryset \
                .filter(project_id=self.kwargs.get('project_id')) \
                .filter(author=self.request.user)


Crispy Forms
------------

If you are using DRF's browsable API or admin API you may also want to install ``django-crispy-forms``, which will enhance the presentation of the filter forms in HTML views, by allowing them to render Bootstrap 3 HTML. Note that this isn't actively supported, although pull requests for bug fixes are welcome.

.. code-block:: bash

    pip install django-crispy-forms

With crispy forms installed and added to Django's ``INSTALLED_APPS``, the browsable API will present a filtering control for ``DjangoFilterBackend``, like so:

.. image:: ../assets/form.png


Additional ``FilterSet`` Features
---------------------------------

The following features are specific to the rest framework FilterSet:

- ``BooleanFilter``'s use the API-friendly ``BooleanWidget``, which accepts lowercase ``true``/``false``.
- Filter generation uses ``IsoDateTimeFilter`` for datetime model fields.
- Raised ``ValidationError``'s are reraised as their DRF equivalent.