从0学DRF：源码剖析与实战（三）-----权限

源码过程分析

由于CBV中，请求是先从dispatch()方法进去，我们像第一篇中研究认证一样，先看dispatch()的源码

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

上一篇讲过，先封装request，然后执行initial()方法，initial()源码如下

def initial(self, request, *args, **kwargs):
    """
    Runs anything that needs to occur prior to calling the method handler.
    """
    self.format_kwarg = self.get_format_suffix(**kwargs)

    # Perform content negotiation and store the accepted info on the request
    neg = self.perform_content_negotiation(request)
    request.accepted_renderer, request.accepted_media_type = neg

        # Determine the API version, if versioning is in use.
        version, scheme = self.determine_version(request, *args, **kwargs)
        request.version, request.versioning_scheme = version, scheme

        # Ensure that the incoming request is permitted
        self.perform_authentication(request)
        '''执行完认证，开始进行权限'''
        self.check_permissions(request)
        self.check_throttles(request)

点击check_permissions进去查看源码

    def check_permissions(self, request):
        """
        Check if the request should be permitted.
        Raises an appropriate exception if the request is not permitted.
        """
        """
        循环权限类的实例列表，调用权限类的has_permission方法,
        如果has_permission方法返回True，则认证成功。
        返回False就是认证失败，抛出异常
        """

        for permission in self.get_permissions():
            if not permission.has_permission(request, self):
                """
                这里是从'message'里面拿异常信息，
                我们可以在我们的类里面自己写message，从而实现自定义
                """
                self.permission_denied(
                    request, message=getattr(permission, 'message', None)
                )

接下来点进去看get_permissions()方法，其实从上一篇中大概也可以猜到，这里应该是使用列表生成式生成一个对象列表。

def get_permissions(self):
    """
    Instantiates and returns the list of permissions that this view requires.
    """
    # 实例化permission_classes里的类，返回一个实例化的permisson列表
    return [permission() for permission in self.permission_classes]

然后我们再点进去源码看看permission_classes里面是啥，

permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES

可以看到如果我们自己重写了permission_classes，就用我们自己的，我们自己没有写就用Django rest framework的。
接下来点进去api_settings

api_settings = APISettings(None, DEFAULTS, IMPORT_STRINGS)

然后还是像研究认证过程的源码一样，点DEFAULTS看看源码，看它默认的DEFAULT_PERMISSION_CLASSES

'DEFAULT_PERMISSION_CLASSES': [
    'rest_framework.permissions.AllowAny',
],

用法

1. 创建一个类，必须继承：BasePermission，必须实现：has_permission方法

from rest_framework.permissions import BasePermission

class SVIPPermission(BasePermission):
	message = "必须是SVIP才能访问"  # 这个信息postman会输出
	def has_permission(self,request,view):
		if request.user.user_type != 3:
			return False
		return True
- 返回值：	
	- True, 有权访问
	- False，无权访问
- 权限局部使用
	class UserInfoView(APIView):
		"""
		订单相关业务（普通用户、VIP）
		"""
		permission_classes = [MyPermission1, ]

		def get(self,request,*args,**kwargs):
			return HttpResponse('用户信息')

- 权限全局使用 
	REST_FRAMEWORK = {
		"DEFAULT_PERMISSION_CLASSES":['api.utils.permission.SVIPPermission']
	}