RestFramework之视图组件

一、视图组件的使用

　　在我们自己书写视图类时需要不断书写重复冗余的代码，看起来十分繁琐不简洁易见，当然rest_framework中的视图组件帮我们做到了一些必要的步骤，使我们节省了编写冗余代码的时间。

　　1.视图组件的导入

from rest_framework import generics     # generics.GenericAPIView 里面封装了APIView
from rest_framework.mixins import (
    ListModelMixin,                     # ListModelMixin表示get请求,获取全部数据
    CreateModelMixin,                   # CreateModelMixin表示post请求，添加数据
    DestroyModelMixin,                  # DestroyModelMixin表示delete请求,删除数据
    UpdateModelMixin,                   # UpdataModelMixin表示put请求，修改数据
    RetrieveModelMixin                  # RetrieveModelMixin表示get请求，获取单条数据
)

　　2.视图组件的使用　

# 视图组件优化第一版
class BookListView(ListModelMixin, CreateModelMixin, generics.GenericAPIView):
    '''
    使用组件的步骤:
        1.获取queryset对象
        2.绑定序列化类
    '''
    queryset = Book.objects.all()
    serializer_class = BookSerializer

    def get(self, request, *args, **kwargs):
        return self.list(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        return self.create(request, *args, **kwargs)

class BookFilterView(RetrieveModelMixin, DestroyModelMixin, UpdateModelMixin, generics.GenericAPIView):
    queryset = Book.objects.all()
    serializer_class = BookSerializer

    def get(self, request, *args, **kwargs):
        # print(self.kwargs) {'pk': '1'}
        return self.retrieve(request, *args, **kwargs)

    def delete(self, request, *args, **kwargs):
        return self.destroy(request, *args, **kwargs)

    def put(self, request, *args, **kwargs):
        return self.update(request, *args, **kwargs)

　　是不是觉得视图组件帮我们做到了很多麻烦的事，还没完下面是改进版，

# 第二版本
class BookView(generics.ListCreateAPIView):
    queryset = Book.objects.all()
    serializer_class = BookSerializer

class BookFilterView(generics.RetrieveUpdateDestroyAPIView):
    queryset = Book.objects.all()
    serializer_class = BookSerializer

　　不用我们自己写每个请求的方法了，去看看源码：其实是源码帮我们写了 我们要写的了。

class ListCreateAPIView(mixins.ListModelMixin,
                        mixins.CreateModelMixin,
                        GenericAPIView):
    """
    Concrete view for listing a queryset or creating a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.list(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        return self.create(request, *args, **kwargs)

class RetrieveUpdateAPIView(mixins.RetrieveModelMixin,
                            mixins.UpdateModelMixin,
                            GenericAPIView):
    """
    Concrete view for retrieving, updating a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    def put(self, request, *args, **kwargs):
        return self.update(request, *args, **kwargs)

    def patch(self, request, *args, **kwargs):
        return self.partial_update(request, *args, **kwargs)

　　但是，我们还是要写两个这个：

    queryset = Book.objects.all()
    serializer_class = BookSerializer

最终版本:

　　

　　在使用时需要注意url中需要对每个请求类型声明

　　url:

 re_path(r'book/$', views.BookView.as_view({
        'get': 'list',
        'post': 'create'
    })),
    re_path(r'book/(?P<pk>\d+)/$', views.BookView.as_view({
        'get': 'retrieve',
        'put': 'update',
        'delete': 'destroy'
    }))
    # 注:在使用ModelViewSet时需要在as_view()中声明请求对应的视图方法，如:get请求对应list ( ListModelMixin )
]

　　导入与使用:

from rest_framework.viewsets import ModelViewSet            #ModelViewSet 里面既封装了mixins又封装了generics中的方法

# 终极版
class BookView(ModelViewSet):
    queryset = Book.objects.all()
    serializer_class = BookSerializer

只需要导入ModelViewSet就可以解决我们麻烦的冗余代码，看看源码怎么帮我们解决的:　　

　　第一步： ModelViewSet类， 继承了放有具体执行每种操作的类(list, create, update, destroy, retrieve)

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

　　第二步：GenericViewSet， 这个类啥都没看，继续看父类

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

　　第三步： ViewSetMixin

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

        # 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))

        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():    # actions ---> {"get": "list", "post": "create"}   {"put": "update", "delete": "destroy", "get": "retrieve"}
                handler = getattr(self, action) # 第一种get请求  self.list = getattr(self, list)  第二种 get请求  self.retrieve = getattr(self, retrieve)
                setattr(self, method, handler)  # 第一种get请求 self.get = self.list  第二种get请求  self.get = self.retrieve

            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)

　　这个类里面有as_view(cls, actions=None, **initkwargs)方法， 也就是我们的url里面写的as_view({"get": "list", "post": "create"}),执行的是这个类中的as_view()方法，而不是APIView种的as_view()方法了！

把那个参数字典传给actions,在放回的view函数中，把每种请求要执行的那种方法 setattr()设置了（看代码中注释）；

然后当用户来访问时，执行那个view函数，正常执行dispatch()方法，根据请求方式分发到每种请求的方法中，这次这个方法，是使用setattr()方法设置给self的，没有具体写，也就能正常执行每种方法了。