官网：https://www.django-rest-framework.org/api-guide/viewsets/

在django rest framework 视图中一共有N个类

第一类：APIview

class IndexView(APIView):

    def get(self,request,*args,**kwargs):

        pk = kwargs.get('pk')

        if pk:

            queryset = models.UserInfo.objects.get(pk=pk)

            ser = UserInfoSerializer(instance=queryset,many=False)

        else:

            queryset = models.UserInfo.objects.all()

            ser = UserInfoSerializer(instance=queryset,many=True)

        return Response(ser.data)

#

这种直接继承了APIView，是最原始的。请求方式就是那五种，get,post,put,patch,delete

第二类 GenericAPIView

class IndexView(GenericAPIView):

    queryset = models.UserInfo.objects.all()

    serializer_class = UserInfoSerializer

    lookup_field = 'pk'

    def get(self,request,*args,**kwargs):

        pk = kwargs.get('pk')

        if pk:

            users = self.filter_queryset(queryset=models.UserInfo.objects.get(pk=pk))

            ser = self.get_serializer(instance=users)

        else:

            users = self.get_queryset()

            ser = self.get_serializer(instance=users,many=True)

        return Response(ser.data)

在GenericAPIView中要重写一些字段和方法，不常用。

第三类 GenericViewSet

class IndexView(GenericViewSet):

    serializer_class = UserInfoSerializer

    queryset = models.UserInfo.objects.all()

    def create(self,request,*args,**kwargs):

        pass

    def list(self,request,*args,**kwargs):  # 获取列表数据

        users = models.UserInfo.objects.all()

        ser = UserInfoSerializer(instance=users,many=True)

        return Response(ser.data)

    def retrieve(self,request,*args,**kwargs):  # 获取单条数据

        pk = kwargs.get('pk')

        users = models.UserInfo.objects.get(pk=pk)

        ser = UserInfoSerializer(instance=users,many=False)

        return Response(ser.data)

    def destroy(self,request,*args,**kwargs):

        pass

    def update(self,request,*args,**kwargs):

        pass

    def partial_update(self,request,*args,**kwargs):

        pass

这个类继承了ViewSetMixin, generics.GenericAPIView，其中在ViewSetMixin中会重写as_view()方法，因此可以将URL中的请求方式与视图函数绑定到一起，在urls.py中以键值对的方式存在：
urls.py

from django.conf.urls import url

from django.contrib import admin

from app01 import  views

urlpatterns = [

    # url(r'^admin/', admin.site.urls),

    url(r'^hehe/', views.hehe),

    url(r'^index/$', views.IndexView.as_view({'get':'list','post':'create'})),

    url(r'^index/(?P<pk>\d+)/$', views.IndexView.as_view({'get':'retrieve','put':'update','patch':'partial_update','delete':'destroy'})),

]

ViewSetMixin源码部分：

class ViewSetMixin(object):

    """

    This is the magic.

    Overrides `.as_view()` so that it takes an `actions` keyword that performs

    the binding of HTTP methods to actions on the Resource.

    For example, to create a concrete view binding the 'GET' and 'POST' methods

    to the 'list' and 'create' actions...

    view = MyViewSet.as_view({'get': 'list', 'post': 'create'})

    """

    @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 suffix initkwarg is reserved for displaying the viewset type.

        # eg. 'List' or 'Instance'.

        cls.suffix = 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))

        def view(request, *args, **kwargs):

            self = cls(**initkwargs)

            # 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)  # 通过反射获取请求方式

                setattr(self, method, handler) # 绑定到视图函数中的方法

            if hasattr(self, 'get') and not hasattr(self, 'head'):

                self.head = self.get

            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.suffix = initkwargs.get('suffix', None)

        view.actions = actions

        return csrf_exempt(view)

    def initialize_request(self, request, *args, **kwargs):

        """

        Set the `.action` attribute on the view,

        depending on the request method.

        """

        request = super(ViewSetMixin, self).initialize_request(request, *args, **kwargs)

        method = request.method.lower()

        if method == 'options':

            # This is a special case as we always provide handling for the

            # options method in the base `View` class.

            # Unlike the other explicitly defined actions, 'metadata' is implicit.

            self.action = 'metadata'

        else:

            self.action = self.action_map.get(method)

        return request

    def reverse_action(self, url_name, *args, **kwargs):

        """

        Reverse the action for the given `url_name`.

        """

        url_name = '%s-%s' % (self.basename, url_name)

        kwargs.setdefault('request', self.request)

        return reverse(url_name, *args, **kwargs)

第四类 ModelViewSet 继承了这个类，ModelViewSet继承了四个混入类和一个泛类，

将会获得增删改查的所有方法。

class IndexView(ModelViewSet):

    queryset = models.UserInfo.objects.all()

    serializer_class = UserInfoSerializer

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

使用类视图的好处：
1、我们将各个HTTP请求方法之间，做了更好的分离。
2、可以很容易地，组成可重复使用的行为。