Django的rest_framework的视图之基于ModelViewSet视图源码解析

前言

今天一直在整理Django的rest_framework的序列化组件，前面一共写了2篇博客，前面的博客给的方案都是一个中间的状态的博客，其中有很多的冗余的代码，如果有朋友不清楚，可以先看下我前面的博客

第一篇，使用minix类来实现序列化和反序列化

https://www.cnblogs.com/bainianminguo/p/10463741.html

第二篇，使用通用的类的方法实现序列化和反序列化

https://www.cnblogs.com/bainianminguo/p/10463784.html

这篇我给大家介绍一个终极方案，基于ModelViewSet的序列化和反序列化的方案和源码解析

正文

终极方案之需要一个类就可以分别处理model对象的删改查操作，和queryset对象的增和查操作

先把具体的代码贴上来，让大家有一个整体的概念，然后我一一给大家分析

一、代码

1、首先urls文件

from django.conf.urls import url
from django.contrib import admin
from django.conf.urls import include
from app1 import views
app_name = "app1"
urlpatterns = [
    url(r'^test/', views.test),
    url(r'^test_cbv/', views.test_cbv.as_view(),name="test1"),
    url(r'^test_rest/', views.Rest_view.as_view(),name="test2"),
    url(r'^book_cbv/', views.Book_cbv.as_view(),name="test3"),
    url(r'^publish_detail_cbv/(?P<id>\d+)', views.Pub_detail_cbv.as_view(),name="publish_url_name"),
    url(r'^book_detail_cbv/(?P<id>\d+)', views.Book_detail_cbv.as_view(),name="test4"),
    # url(r'^autherdetail/(?P<id>\d+)', views.Book_detail_cbv.as_view(), name="autherdetail"),
    # url(r'^auther/', views.Book_cbv.as_view(),name="auther"),

    url(r'^autherdetail/(?P<pk>\d+)/', views.AutherModelCBV.as_view({"get":"retrieve","delete":"destroy","put":"update"}), name="autherdetail"),
    url(r'^auther/', views.AutherModelCBV.as_view({"get":"list","post":"create"}),name="auther"),
]

　　

我们用的url是最后两条

我们仔细观察一下，这里的url和之前有3个地方不一样，我一一给大家指出来

a、两个url对应的类是相同的类

b、as_view这个方法有参数，这个参数是一个字典

c、对于model对象的url的url中的变量的名称是pk，之前我们用的id

2、序列化类的代码

class authermodelserializer(serializers.ModelSerializer):
    class Meta:
        model = models.Auther
        fields = "__all__"

序列化的类的代码和之前的保持一致，没有任何改变

3、视图类的代码

from rest_framework import viewsets

class AutherModelCBV(viewsets.ModelViewSet):
    queryset = models.Auther.objects.all()
    serializer_class = authermodelserializer

　　

我们可以看到这个类非常的简单，这个类继承了一个新的类，我们之前没有用过这个类：viewsets.ModelViewSet

二、流程和源码解析

1、从url的as_view方法开始解读

as_view的源码

    @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 confiugurations. 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)
            # 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)

            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.actions = actions
        return csrf_exempt(view)

　　

函数的代码很长，我们只关注需要我们关注的代码

首先，确定as_view的函数中action的值就是我们的urls中as_view方法中的字典

action的值就是as_view方法中的字典，不信你可以实际测试一下

然后我们看下as_view这个方法的返回值

然后我们在看下as_view中的view方法

        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)
                setattr(self, method, handler)

            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)

　　

这里很重要，我们要慢慢来分析

然后在看下view这个方法的返回值

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

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

　　

我们可以看到这个函数的返回值是self.dispatch

我们注意到self.dispatch这个方法，在as_view和view均找不到，这个self是什么呢？这个self就是视图函数的类，所以我们来我们的视图函数的类中找下

明显我们自定义的AuhterModelCBV这个类没有dispatch这个方法，所以我们要去这个类的父类中查找，也就是viewsets.ModelViewSet类中查找

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

　　

这个类中也没有dispatch方法，但是这个类又继承了6个类，由于继承是从左到右继承，我们从最左边的类开始查找，最终在GeneriViewSet中找到dispatch的方法

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

　　

GeneriViewSet的类中也没有dispatch方法，但是这个类有2个父类，所以我们继续往上找

最终在GenericAPIView类中找到了dispatch方法

这个类中也没有dispatch方法，我们在往他的父类中查找

最后，我们终于在APIView类中找到我们需要的dispatch方法

class APIView(View):
        def dispatch(self, request, *args, **kwargs):
        """
        `.dispatch()` is pretty much the same as Django's regular dispatch,
        but with extra hooks for startup, finalize, and exception handling.
        """
        self.args = args
        self.kwargs = kwargs
        request = self.initialize_request(request, *args, **kwargs)
        self.request = request
        self.headers = self.default_response_headers  # deprecate?

        try:
            self.initial(request, *args, **kwargs)

            # Get the appropriate handler method
            if request.method.lower() in self.http_method_names:
                handler = getattr(self, request.method.lower(),
                                  self.http_method_not_allowed)
            else:
                handler = self.http_method_not_allowed

            response = handler(request, *args, **kwargs)

        except Exception as exc:
            response = self.handle_exception(exc)

        self.response = self.finalize_response(request, response, *args, **kwargs)
        return self.response

　　

下面在看下dispatch方法干了什么

所以执行self.create等方法就会调用我们前面已经对应的self.list。self.update等方法

至此，终极方案我们也完成了！谢谢大家的查阅！