[docs] Added django-filter docs

README.rst

@@ -977,6 +977,43 @@ which is inheriting any of the mixin classes.
 Usage example: `organization_field
 <https://github.com/openwisp/openwisp-users#organization_field>`_.
 
+Django Filters Multi-tenant serializers for the browsable web UI
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Integration of `Django Filter <https://django-filter.readthedocs.io/en/stable/guide/rest_framework.html>`_
+with `Django REST Framework <https://www.django-rest-framework.org/>`_
+is provided through a DRF-specific FilterSet and a filter backend.
+
+The relationship fields in ``django-filters`` options interface shows all the
+relationships, without filtering by the organization the user has access to, which
+breaks multi-tenancy.
+
+The ``FilterDjangoByOrgMembership``, ``FilterDjangoByOrgManaged``
+and ``FilterDjangoByOrgOwned`` can be used to solve this issue.
+
+Usage example:
+
+.. code-block:: python
+
+   from openwisp_users.api.mixins import FilterDjangoByOrgManaged
+   from ..models import FloorPlan
+
+
+   class FloorPlanOrganizationFilter(FilterDjangoByOrgManaged):
+       organization_slug = filters.CharFilter(field_name='organization__slug')
+
+       class Meta:
+           model = FloorPlan
+           fields = ['organization', 'organization_slug']
+
+
+   class FloorPlanListCreateView(ProtectedAPIMixin, generics.ListCreateAPIView):
+       serializer_class = FloorPlanSerializer
+       queryset = FloorPlan.objects.select_related().order_by('-created')
+       pagination_class = ListViewPagination
+       filter_backends = [filters.DjangoFilterBackend]
+       filterset_class = FloorPlanOrganizationFilter
+
 Admin Multitenancy mixins
 -------------------------