Restframework笔记——dispatch源码分析

系统管理员 2023-06-20 12:58 59阅读 0赞

CBV基于反射实现根据请求方式不同，执行不同的方法。  
大体流程为：url -> view方法 -> dispatch方法（反射执行其他：GET/POST/DELETE/PUT）  
其中url ->view方法，本身父类View中的as\_view(cls, \*\*initkwargs)中又有一个view(),并且as\_view()返回的就是view()

@classonlymethod
        def as_view(cls, **initkwargs):
            """Main entry point for a request-response process."""
            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)   # 实例化原类视图
                if hasattr(self, 'get') and not hasattr(self, 'head'):
                    self.head = self.get
                self.setup(request, *args, **kwargs)
                if not hasattr(self, 'request'):
                    raise AttributeError(
                        "%s instance has no 'request' attribute. Did you override "
                        "setup() and forget to call super()?" % cls.__name__
                    )
                # 调用dispatch并返回
                return self.dispatch(request, *args, **kwargs)
            view.view_class = cls
            view.view_initkwargs = initkwargs
    
            # 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=())
            return view   # 返回view

而view(request, \*args, \*\*kwargs)中先实例化请求的类：

self = cls(**initkwargs)

然后调用dispatch(),并返回

return self.dispatch(request, *args, **kwargs)

下面为dispatch源码：

def dispatch(self, request, *args, **kwargs):
            # Try to dispatch to the right method; if a method doesn't exist,
            # defer to the error handler. Also defer to the error handler if the
            # request method isn't on the approved list.
            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
            return handler(request, *args, **kwargs)

所以本质上还是找dispatch(),首先去自身里面找dispatch,如果有，不往下找了，如果没有，继续去父类中一层一层往下找dispatch。找到dispatch后通过getattr()再执行get或post等.其中getattr()的形参位request.method.lower()，是因为请求的为“GET”等都是大写，需要转成小写。 下面的代码中自身中已经重写了dispatch(),则不再往下找了。

class StudentsView(View):
    	def dispatch(self, request, *args, **kwargs):
    		handler = getattr(self, request.method.lower())
    		return handler(request, *args, **kwargs)
    		''' 这种可以执行父类的dispatch 流程：请求->原类视图自己的disaptch->父类的dispatch,然后父类的dispatch(self,request, *args, **kwargs)根据self又返回到原类对象中去找对应的get或post等方法，获取结果返回给父类的dispatch->原类视图中的dispatch->用户 ret = super(StudentsView,self).dispatch(request, *args, **kwargs) '''
    	def get(self,request,*args,**kwargs):
    		return HttpResponse('GET')
    
    	def post(self, request, *args, **kwargs):
    		return HttpResponse('POST')
    
    	def put(self, request, *args, **kwargs):
    		return HttpResponse('PUT')
    
    	def delete(self, request, *args, **kwargs):
    		return HttpResponse('DELETE')