Py009-01-02CBV基本使用

CBV结构实现的原理

StudentsView 的 get/post等方法如何调用的呢？

  • 反射——(反射代码在哪里？)
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from django.views import  View;
class StudentsView(View):
    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');

urls.py里 as_view函数 

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# 在路由系统里永远是 一个url 对应一个函数
urlpatterns = [
    re_path(r'^students/', views.StudentsView.as_view())
]
# views.StudentsView.as_view() 返回一个函数
# StudentsView 本身没有 as_view 方法 => 它的父类 View 里

View 源码里的 as_view

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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))
    # 定义了一个view 函数并返回
    def view(request, *args, **kwargs):
        # cls就是当前请求的类 StudentsView
        # self = StudentsView() 实例化
        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
        # 返回当前的 dispatch 方法 =》 一个请求进来实际是执行 dispatch
        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

dispatch

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class View:
    http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']

    def dispatch(self, request, *args, **kwargs):
        # 获取请求方式 get/post/put/delete
        if request.method.lower() in self.http_method_names:
            # 反射
            handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
        else:
            handler = self.http_method_not_allowed
        return handler(request, *args, **kwargs)

经典面试题：你知道的http请求方式有哪些

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[
    'get',    #查
    'post',   #增加
    'put',    #更新
    'patch',  #局部
    'delete', #删除
    'head', 
    'options', 
    'trace'
]

原理

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url => view方法 => dispatch方法 => (反射执行其他 get/post/put/delete)
  • 请求进来要先执行 dispatch方法

定制自己的 dispatch 方法

  • 触发 dispatch 之前/之后 做一些操作
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from django.views import  View;
class StudentsView(View):
    def dispatch(self, request, *args, **kwargs):
        # 调用 父类的 dispatch
        print('before')
        ret = super(StudentsView,self).dispatch(request, *args, **kwargs)
        print('after')
        return ret

    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');

多个类公用功能，为了避免重复编写

假如此时有个TeachersView,这样要复制两份dispatch

  • 使用继承
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class MyBaseView(object):
    def dispatch(self, request, *args, **kwargs):
        # 调用 父类的 dispatch
        print('before')
        ret = super(StudentsView, self).dispatch(request, *args, **kwargs)
        print('after')
        return ret

class StudentsView(MyBaseView,View):

    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');


class TeachersView(MyBaseView,View):

    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');