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332 lines
14 KiB
Markdown
332 lines
14 KiB
Markdown
---
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source:
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- viewsets.py
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---
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# ViewSets
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> After routing has determined which controller to use for a request, your controller is responsible for making sense of the request and producing the appropriate output.
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>
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> — [Ruby on Rails Documentation][cite]
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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'.
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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()`.
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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.
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Typically, rather than explicitly 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.
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## Example
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Let's define a simple viewset that can be used to list or retrieve all the users in the system.
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from django.contrib.auth.models import User
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from django.shortcuts import get_object_or_404
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from myapps.serializers import UserSerializer
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from rest_framework import viewsets
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from rest_framework.response import Response
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class UserViewSet(viewsets.ViewSet):
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"""
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A simple ViewSet for listing or retrieving users.
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"""
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def list(self, request):
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queryset = User.objects.all()
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serializer = UserSerializer(queryset, many=True)
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return Response(serializer.data)
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def retrieve(self, request, pk=None):
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queryset = User.objects.all()
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user = get_object_or_404(queryset, pk=pk)
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serializer = UserSerializer(user)
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return Response(serializer.data)
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If we need to, we can bind this viewset into two separate views, like so:
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user_list = UserViewSet.as_view({'get': 'list'})
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user_detail = UserViewSet.as_view({'get': 'retrieve'})
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Typically we wouldn't do this, but would instead register the viewset with a router, and allow the urlconf to be automatically generated.
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from myapp.views import UserViewSet
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from rest_framework.routers import DefaultRouter
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router = DefaultRouter()
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router.register(r'users', UserViewSet, basename='user')
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urlpatterns = router.urls
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Rather than writing your own viewsets, you'll often want to use the existing base classes that provide a default set of behavior. For example:
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class UserViewSet(viewsets.ModelViewSet):
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"""
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A viewset for viewing and editing user instances.
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"""
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serializer_class = UserSerializer
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queryset = User.objects.all()
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There are two main advantages of using a `ViewSet` class over using a `View` class.
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* 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.
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* By using routers, we no longer need to deal with wiring up the URL conf ourselves.
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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.
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## ViewSet actions
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The default routers included with REST framework will provide routes for a standard set of create/retrieve/update/destroy style actions, as shown below:
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class UserViewSet(viewsets.ViewSet):
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"""
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Example empty viewset demonstrating the standard
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actions that will be handled by a router class.
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If you're using format suffixes, make sure to also include
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the `format=None` keyword argument for each action.
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"""
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def list(self, request):
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pass
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def create(self, request):
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pass
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def retrieve(self, request, pk=None):
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pass
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def update(self, request, pk=None):
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pass
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def partial_update(self, request, pk=None):
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pass
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def destroy(self, request, pk=None):
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pass
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## Introspecting ViewSet actions
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During dispatch, the following attributes are available on the `ViewSet`.
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* `basename` - the base to use for the URL names that are created.
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* `action` - the name of the current action (e.g., `list`, `create`).
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* `detail` - boolean indicating if the current action is configured for a list or detail view.
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* `suffix` - the display suffix for the viewset type - mirrors the `detail` attribute.
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* `name` - the display name for the viewset. This argument is mutually exclusive to `suffix`.
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* `description` - the display description for the individual view of a viewset.
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You may inspect these attributes to adjust behavior based on the current action. For example, you could restrict permissions to everything except the `list` action similar to this:
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def get_permissions(self):
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"""
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Instantiates and returns the list of permissions that this view requires.
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"""
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if self.action == 'list':
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permission_classes = [IsAuthenticated]
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else:
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permission_classes = [IsAdminUser]
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return [permission() for permission in permission_classes]
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## Marking extra actions for routing
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If you have ad-hoc methods that should be routable, you can mark them as such with the `@action` decorator. Like regular actions, extra actions may be intended for either a single object, or an entire collection. To indicate this, set the `detail` argument to `True` or `False`. The router will configure its URL patterns accordingly. e.g., the `DefaultRouter` will configure detail actions to contain `pk` in their URL patterns.
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A more complete example of extra actions:
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from django.contrib.auth.models import User
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from rest_framework import status, viewsets
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from rest_framework.decorators import action
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from rest_framework.response import Response
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from myapp.serializers import UserSerializer, PasswordSerializer
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class UserViewSet(viewsets.ModelViewSet):
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"""
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A viewset that provides the standard actions
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"""
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queryset = User.objects.all()
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serializer_class = UserSerializer
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@action(detail=True, methods=['post'])
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def set_password(self, request, pk=None):
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user = self.get_object()
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serializer = PasswordSerializer(data=request.data)
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if serializer.is_valid():
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user.set_password(serializer.validated_data['password'])
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user.save()
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return Response({'status': 'password set'})
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else:
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return Response(serializer.errors,
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status=status.HTTP_400_BAD_REQUEST)
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@action(detail=False)
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def recent_users(self, request):
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recent_users = User.objects.all().order_by('-last_login')
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page = self.paginate_queryset(recent_users)
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if page is not None:
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serializer = self.get_serializer(page, many=True)
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return self.get_paginated_response(serializer.data)
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serializer = self.get_serializer(recent_users, many=True)
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return Response(serializer.data)
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The `action` decorator will route `GET` requests by default, but may also accept other HTTP methods by setting the `methods` argument. For example:
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@action(detail=True, methods=['post', 'delete'])
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def unset_password(self, request, pk=None):
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...
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Argument `methods` also supports HTTP methods defined as [HTTPMethod](https://docs.python.org/3/library/http.html#http.HTTPMethod). Example below is identical to the one above:
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from http import HTTPMethod
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@action(detail=True, methods=[HTTPMethod.POST, HTTPMethod.DELETE])
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def unset_password(self, request, pk=None):
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...
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The decorator allows you to override any viewset-level configuration such as `permission_classes`, `serializer_class`, `filter_backends`...:
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@action(detail=True, methods=['post'], permission_classes=[IsAdminOrIsSelf])
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def set_password(self, request, pk=None):
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...
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The two new actions will then be available at the urls `^users/{pk}/set_password/$` and `^users/{pk}/unset_password/$`. Use the `url_path` and `url_name` parameters to change the URL segment and the reverse URL name of the action.
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To view all extra actions, call the `.get_extra_actions()` method.
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### Routing additional HTTP methods for extra actions
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Extra actions can map additional HTTP methods to separate `ViewSet` methods. For example, the above password set/unset methods could be consolidated into a single route. Note that additional mappings do not accept arguments.
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```python
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@action(detail=True, methods=["put"], name="Change Password")
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def password(self, request, pk=None):
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"""Update the user's password."""
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...
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@password.mapping.delete
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def delete_password(self, request, pk=None):
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"""Delete the user's password."""
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...
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```
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## Reversing action URLs
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If you need to get the URL of an action, use the `.reverse_action()` method. This is a convenience wrapper for `reverse()`, automatically passing the view's `request` object and prepending the `url_name` with the `.basename` attribute.
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Note that the `basename` is provided by the router during `ViewSet` registration. If you are not using a router, then you must provide the `basename` argument to the `.as_view()` method.
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Using the example from the previous section:
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```pycon
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>>> view.reverse_action("set-password", args=["1"])
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'http://localhost:8000/api/users/1/set_password'
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```
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Alternatively, you can use the `url_name` attribute set by the `@action` decorator.
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```pycon
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>>> view.reverse_action(view.set_password.url_name, args=['1'])
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'http://localhost:8000/api/users/1/set_password'
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```
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The `url_name` argument for `.reverse_action()` should match the same argument to the `@action` decorator. Additionally, this method can be used to reverse the default actions, such as `list` and `create`.
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---
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# API Reference
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## ViewSet
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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.
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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.
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## GenericViewSet
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The `GenericViewSet` class inherits from `GenericAPIView`, and provides the default set of `get_object`, `get_queryset` methods and other generic view base behavior, but does not include any actions by default.
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In order to use a `GenericViewSet` class you'll override the class and either mixin the required mixin classes, or define the action implementations explicitly.
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## ModelViewSet
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The `ModelViewSet` class inherits from `GenericAPIView` and includes implementations for various actions, by mixing in the behavior of the various mixin classes.
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The actions provided by the `ModelViewSet` class are `.list()`, `.retrieve()`, `.create()`, `.update()`, `.partial_update()`, and `.destroy()`.
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#### Example
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Because `ModelViewSet` extends `GenericAPIView`, you'll normally need to provide at least the `queryset` and `serializer_class` attributes. For example:
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class AccountViewSet(viewsets.ModelViewSet):
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"""
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A simple ViewSet for viewing and editing accounts.
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"""
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queryset = Account.objects.all()
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serializer_class = AccountSerializer
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permission_classes = [IsAccountAdminOrReadOnly]
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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:
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class AccountViewSet(viewsets.ModelViewSet):
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"""
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A simple ViewSet for viewing and editing the accounts
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associated with the user.
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"""
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serializer_class = AccountSerializer
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permission_classes = [IsAccountAdminOrReadOnly]
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def get_queryset(self):
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return self.request.user.accounts.all()
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Note however that upon removal of the `queryset` property from your `ViewSet`, any associated [router][routers] will be unable to derive the basename of your Model automatically, and so you will have to specify the `basename` kwarg as part of your [router registration][routers].
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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.
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## ReadOnlyModelViewSet
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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()`.
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#### Example
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As with `ModelViewSet`, you'll normally need to provide at least the `queryset` and `serializer_class` attributes. For example:
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class AccountViewSet(viewsets.ReadOnlyModelViewSet):
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"""
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A simple ViewSet for viewing accounts.
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"""
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queryset = Account.objects.all()
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serializer_class = AccountSerializer
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Again, as with `ModelViewSet`, you can use any of the standard attributes and method overrides available to `GenericAPIView`.
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# Custom ViewSet base classes
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You may need to provide custom `ViewSet` classes that do not have the full set of `ModelViewSet` actions, or that customize the behavior in some other way.
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## Example
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To create a base viewset class that provides `create`, `list` and `retrieve` operations, inherit from `GenericViewSet`, and mixin the required actions:
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from rest_framework import mixins
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class CreateListRetrieveViewSet(mixins.CreateModelMixin,
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mixins.ListModelMixin,
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mixins.RetrieveModelMixin,
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viewsets.GenericViewSet):
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"""
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A viewset that provides `retrieve`, `create`, and `list` actions.
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To use it, override the class and set the `.queryset` and
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`.serializer_class` attributes.
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"""
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pass
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By creating your own base `ViewSet` classes, you can provide common behavior that can be reused in multiple viewsets across your API.
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[cite]: https://guides.rubyonrails.org/action_controller_overview.html
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[routers]: routers.md
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