一、ViewSet

继承APIView和ViewSetMixin；
作用也与APIView基本类似，提供了身份认证、权限校验、流量管理等。
ViewSet在开发接口中不经常用

1、ViewSet源码

在ViewSet中，没有提供任何动作action方法，需要我们自己实现action方法。

class ViewSet(ViewSetMixin, views.APIView):
    """
    The base ViewSet class does not provide any actions by default.
    """
    pass

ViewSet视图集类不再限制视图方法名只允许get()、post()等这种情况了，而是实现允许开发者根据自己的需要定义自定义方法名，例如 list() 、create() 等，然后经过路由中使用http和这些视图方法名进行绑定调用

2、ViewSetMixin源码

ViewSet主要通过继承ViewSetMixin来实现在调用as_view()时传入字典{“http请求”：“视图方法”}的映射处理工作，如
{‘get’:’list’，
‘post’:‘create’,
‘put’:‘update’,
‘delete’:‘destory’}，

	@classonlymethod
    def as_view(cls, actions=None, **initkwargs):
        """
        Because of the way class based views create a closure around the
        instantiated view, we need to totally reimplement `.as_view`,
        and slightly modify the view function that is created and returned.
        """
        # The name and description initkwargs may be explicitly overridden for
        # certain route configurations. eg, names of extra actions.
        cls.name = None
        cls.description = None

        # The suffix initkwarg is reserved for displaying the viewset type.
        # This initkwarg should have no effect if the name is provided.
        # eg. 'List' or 'Instance'.
        cls.suffix = None

        # The detail initkwarg is reserved for introspecting the viewset type.
        cls.detail = None

        # Setting a basename allows a view to reverse its action urls. This
        # value is provided by the router through the initkwargs.
        cls.basename = None

        # actions must not be empty
        if not actions:
            raise TypeError("The `actions` argument must be provided when "
                            "calling `.as_view()` on a ViewSet. For example "
                            "`.as_view({'get': 'list'})`")

        # sanitize keyword arguments
        for key in initkwargs:
            if key in cls.http_method_names:
                raise TypeError("You tried to pass in the %s method name as a "
                                "keyword argument to %s(). Don't do that."
                                % (key, cls.__name__))
            if not hasattr(cls, key):
                raise TypeError("%s() received an invalid keyword %r" % (
                    cls.__name__, key))

        # name and suffix are mutually exclusive
        if 'name' in initkwargs and 'suffix' in initkwargs:
            raise TypeError("%s() received both `name` and `suffix`, which are "
                            "mutually exclusive arguments." % (cls.__name__))

        def view(request, *args, **kwargs):
            self = cls(**initkwargs)

            if 'get' in actions and 'head' not in actions:
                actions['head'] = actions['get']

            # We also store the mapping of request methods to actions,
            # so that we can later set the action attribute.
            # eg. `self.action = 'list'` on an incoming GET request.
            self.action_map = actions

            # Bind methods to actions
            # This is the bit that's different to a standard view
            for method, action in actions.items():
                handler = getattr(self, action)
                setattr(self, method, handler)

            self.request = request
            self.args = args
            self.kwargs = kwargs

            # And continue as usual
            return self.dispatch(request, *args, **kwargs)

        # take name and docstring from class
        update_wrapper(view, cls, updated=())

        # and possible attributes set by decorators
        # like csrf_exempt from dispatch
        update_wrapper(view, cls.dispatch, assigned=())

        # We need to set these on the view function, so that breadcrumb
        # generation can pick out these bits of information from a
        # resolved URL.
        view.cls = cls
        view.initkwargs = initkwargs
        view.actions = actions
        return csrf_exempt(view)

二、ModelViewSet

使用ViewSet通常并不方便，因为list、retrieve、create、update、destory等action
方法都需要自己编写，而这些方法与前面讲过的Mixin扩展类提供的方法同名，所以我们可以通过继承Mixin扩展类来复用这些方法而无需自己编写。

ModelViewSet继承自 GenericViewSet，同时包括了ListModelMixin、RetrieveModelMixin、CreateModelMixin、UpdateModelMixin、DestoryModelMixin。

1、ModelViewSet源码

class ModelViewSet(mixins.CreateModelMixin,
                   mixins.RetrieveModelMixin,
                   mixins.UpdateModelMixin,
                   mixins.DestroyModelMixin,
                   mixins.ListModelMixin,
                   GenericViewSet):
    """
    A viewset that provides default `create()`, `retrieve()`, `update()`,
    `partial_update()`, `destroy()` and `list()` actions.
    """
    pass

三、ReadOnlyModelViewSet

ReadOnlyModelViewSet承自 GenericViewSet，同时包括了ListModelMixin、RetrieveModelMixin。

1、ReadOnlyModelViewSet源码

class ReadOnlyModelViewSet(mixins.RetrieveModelMixin,
                           mixins.ListModelMixin,
                           GenericViewSet):
    """
    A viewset that provides default `list()` and `retrieve()` actions.
    """
    pass

四、GenericViewSet

GenericViewSet继承ViewSetMixin、GenericAPIView
继承ViewSetMixin：实现了在调用as_view()时传入字典{“http请求”：“视图方法”}的映射处理工作，如
{‘get’:’list’，
‘post’:‘create’,
‘put’:‘update’,
‘delete’:‘destory’}，
继承了GenericAPIView：实现了分页、限流、过滤功能

class GenericViewSet(ViewSetMixin, generics.GenericAPIView):
    """
    The GenericViewSet class does not provide any actions by default,
    but does include the base set of generic view behavior, such as
    the `get_object` and `get_queryset` methods.
    """
    pass