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  • Python rest-framework 中类的继承关系(as_view)

    一. 背景

    最近几天一直在学习restful framework的源代码,用户请求的流程,在路由系统这块遇到一个疑问,关于类的继承关系,当请求进来到路由这块,执行as_view()方法的时候,为什么会运行父类View的as_view()方法再执行到APIView的dispatch方法呢?这里记录一下一遍后面方便自己查阅

    二. 代码示例

    1. 路由

    from django.conf.urls import url
    from api import views as api_view
    
    urlpatterns = [
        url(r'^index/', api_view.IndexView.as_view()),
    ]

    2.  视图类

    from rest_framework.response import  Response
    from rest_framework.views import APIView
    
    class IndexView(APIView):
        def get(self,request):
            return Response('...')

    三. 源代码分析

    a. APIView的as_view方法

    class APIView(View):
    
    
        @classmethod
        def as_view(cls, **initkwargs):
          
            if isinstance(getattr(cls, 'queryset', None), models.query.QuerySet):
                def force_evaluation():
                    raise RuntimeError(
                        'Do not evaluate the `.queryset` attribute directly, '
                        'as the result will be cached and reused between requests. '
                        'Use `.all()` or call `.get_queryset()` instead.'
                    )
                cls.queryset._fetch_all = force_evaluation
    
            view = super(APIView, cls).as_view(**initkwargs)
            # 这里是继承了父类的方法as_view()
        
            view.cls = cls
            view.initkwargs = initkwargs
    
            return csrf_exempt(view)

    # 代码太多只截取部分代码

    b. super(APIView,cls).as_view(**initkwargs)执行了什么操作

    # super(APIView,self) 首先找到 APIView的父类(就是类 View),然后把View类的as_view属性 转换为类 APIView的属性
    # 相当于将View中的as_view()中的代码复制到API_View中的as_view中

    所以最终运行 super(APIView,cls).as_view(**initkwargs)执行了View中的as_view方法

    class View(object):
       
    
        http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']
    
        def __init__(self, **kwargs):
           
            for key, value in six.iteritems(kwargs):
                setattr(self, key, value)
    
        @classonlymethod
        def as_view(cls, **initkwargs):
           
            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. as_view "
                                    "only accepts arguments that are already "
                                    "attributes of the class." % (cls.__name__, key))
    
            def view(request, *args, **kwargs):
                self = cls(**initkwargs)
                if hasattr(self, 'get') and not hasattr(self, 'head'):
                    self.head = self.get
                self.request = request
                self.args = args
                self.kwargs = kwargs
                return self.dispatch(request, *args, **kwargs)
                # 运行这里吧最后执行了self.dispatch
            view.view_class = cls
            view.view_initkwargs = initkwargs
    
            update_wrapper(view, cls, updated=())
    
     
            update_wrapper(view, cls.dispatch, assigned=())
            return view       # 返回了view函数
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  • 原文地址:https://www.cnblogs.com/supery007/p/8432324.html
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