<a class="github" href="viewsets.py"></a>

# ViewSets

Django REST framework allows you to combine the logic for a set of related views in a single class, called a `ViewSet`.  In other frameworks you may also find conceptually similar implementations named something like 'Resources' or 'Controllers'.

A `ViewSet` class is simply **a type of class-based View, that does not provide any method handlers** such as `.get()` or `.post()`, and instead provides actions such as `.list()` and `.create()`.

The method handlers for a `ViewSet` are only bound to the corresponding actions at the point of finalizing the view, using the `.as_view()` method.

Typically, rather than exlicitly registering the views in a viewset in the urlconf, you'll register the viewset with a router class, that automatically determines the urlconf for you.

## Example

Let's define a simple viewset that can be used to listing or retrieving all the users in the system.

    class UserViewSet(ViewSet):
        """
        A simple ViewSet that for listing or retrieving users.
        """
        queryset = User.objects.all()

        def list(self, request):
            serializer = UserSerializer(self.queryset, many=True)
            return Response(serializer.data)
            
        def retrieve(self, request, pk=None):
            user = get_object_or_404(self.queryset, pk=pk)
            serializer = UserSerializer(user)
            return Response(serializer.data)

If we need to, we can bind this viewset into two seperate views, like so:

    user_list = UserViewSet.as_view({'get': 'list'})
    user_detail = UserViewSet.as_view({'get': 'retrieve'})

Typically we wouldn't do this, but would instead register the viewset with a router, and allow the urlconf to be automatically generated.

There are two main advantages of using a `ViewSet` class over using a `View` class.

* Repeated logic can be combined into a single class.  In the above example, we only need to specify the `queryset` once, and it'll be used across multiple views.
* By using routers, we no longer need to deal with wiring up the URL conf ourselves.

Both of these come with a trade-off.  Using regular views and URL confs is more explicit and gives you more control.  ViewSets are helpful if you want to get up and running quickly, or when you have a large API and you want to enforce a consistent URL configuration throughout.


# API Reference

## ViewSet

The `ViewSet` class inherits from `APIView`.  You can use any of the standard attributes such as `permission_classes`, `authentication_classes` in order to control the API policy on the viewset.

The `ViewSet` class does not provide any implementations of actions.  In order to use a `ViewSet` class you'll override the class and define the action implementations explicitly.

## ModelViewSet

The `ModelViewSet` class inherits from `GenericAPIView` and includes implementations for various actions, by mixing in the behavior of the

The actions provided by the `ModelViewSet` class are `.list()`, `.retrieve()`,  `.create()`, `.update()`, and `.destroy()`.

#### Example

Because `ModelViewSet` extends `GenericAPIView`, you'll normally need to provide at least the `queryset` and `serializer_class` attributes.  For example:

    class AccountViewSet(viewsets.ModelViewSet):
        """
        A simple ViewSet for viewing and editing accounts.
        """
        queryset = Account.objects.all()
        serializer_class = AccountSerializer
        permission_classes = [IsAccountAdminOrReadOnly]

Note that you can use any of the standard attributes or method overrides provided by `GenericAPIView`.  For example, to use a `ViewSet` that dynamically determines the queryset it should operate on, you might do something like this:

    class AccountViewSet(viewsets.ModelViewSet):
        """
        A simple ViewSet for viewing and editing the accounts
        associated with the user.
        """
        serializer_class = AccountSerializer
        permission_classes = [IsAccountAdminOrReadOnly]

        def get_queryset(self):
            return request.user.accounts.all()

Also note that although this class provides the complete set of create/list/retrieve/update/destroy actions by default, you can restrict the available operations by using the standard permission classes.

## ReadOnlyModelViewSet

The `ReadOnlyModelViewSet` class also inherits from `GenericAPIView`.  As with `ModelViewSet` it also includes implementations for various actions, but unlike `ModelViewSet` only provides the 'read-only' actions, `.list()` and `.retrieve()`.

#### Example

As with `ModelViewSet`, you'll normally need to provide at least the `queryset` and `serializer_class` attributes.  For example:

    class AccountViewSet(viewsets.ReadOnlyModelViewSet):
        """
        A simple ViewSet for viewing accounts.
        """
        queryset = Account.objects.all()
        serializer_class = AccountSerializer

Again, as with `ModelViewSet`, you can use any of the standard attributes and method overrides available to `GenericAPIView`.

# Custom ViewSet base classes 

Any standard `View` class can be turned into a `ViewSet` class by mixing in `ViewSetMixin`.  You can use this to define your own base classes.

For example, the definition of `ModelViewSet` looks like this:

    class ModelViewSet(mixins.CreateModelMixin,
                       mixins.RetrieveModelMixin,
                       mixins.UpdateModelMixin,
                       mixins.DestroyModelMixin,
                       mixins.ListModelMixin,
                       viewsets.ViewSetMixin,
                       generics.GenericAPIView):
        """
        A viewset that provides actions for `create`, `retrieve`,
        `update`, `destroy` and `list` actions.
        
        To use it, override the class and set the `.queryset`
        and `.serializer_class` attributes.
        """
        pass

By creating your own base `ViewSet` classes, you can provide common behavior that can be reused in multiple views across your API.

For advanced usage, it's worth noting the that `ViewSetMixin` class can also be applied to the standard Django `View` class.  Doing so allows you to use REST framework's automatic routing, but don't want to use it's permissions, authentication and other API policies.

---

# Routers

Routers provide a convenient and simple shortcut for wiring up your application's URLs.

    router = routers.DefaultRouter()
    router.register('^/', APIRoot, 'api-root')
    router.register('^users/', UserViewSet, 'user')
    router.register('^groups/', GroupViewSet, 'group')
    router.register('^accounts/', AccountViewSet, 'account')

    urlpatterns = router.urlpatterns

[cite]: http://guides.rubyonrails.org/routing.html