class View: def http_method_not_allowed(self, request, *args, **kwargs): logger.warning( 'Method Not Allowed (%s): %s', request.method, request.path, extra={'status_code': 405, 'request': request} ) return HttpResponseNotAllowed(self._allowed_methods())比如当一个类视图函数之定义了 get 方法,而没有定义 post 方法,那么这个类视图函数接收到 post 的请求的时候,由于找不到相对应的 post 的定义,就会通过另一个方法 dispatch 分发到 http_method_not_allowed 方法中。
class View: def dispatch(self, request, *args, **kwargs): 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)http_method_names 定义当前 View可以接受的请求类型:
http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']首先,if 判断当前的请求类型是否可以被接受,即请求方是否定义在 http_method_names 变量中。若能够接受请求,则 dispatch() 尝试获取 View 中的同名方法,如果不存在,则将 handler 指定为 http_method_not_allowed 即不被允许的方法。然后 else 规定如果方法不被接受则直接将其指定为 http_method_not_allowed。
@classonlymethod
装饰器,作用是只允许类对象调用这个方法,如果是类实例调用,将会抛出 AttributeError 异常。该方法的源码如下所示:
class View: @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): #创建View类实例 self = cls(**initkwargs) 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View实例的dispatch方法 return self.dispatch(request, *args, **kwargs) view.view_class = cls view.view_initkwargs = initkwargs update_wrapper(view, cls, updated=()) update_wrapper(view, cls.dispatch, assigned=()) return viewDjango 将一个 HTTP 请求映射到一个可调用的函数,而不是一个类对象。所以,在定义 URL 路由的时候总是需要调用 View 的 as_view 方法。可以看到,上述的as_view 方法,它创建了 View 类的实例,然后调用了 dispatch 方法,根据请求类型分发处理请求函数。
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