Django REST为文件属性输出完整URL的方法

{
 "id": 1,
 "nickname": "管理员",
 "mobilephone": "1234567890",
 "avatar": "/media/profiles/2017/12/17/avatar.png"
}

class ProfileView(APIView):
 def get(self, request):
  user = request.user
  if user.is_authenticated:
   profile = Profile.objects.get(user=user)
   return Response(ProfileSerializer(profile).data)
  else:
   raise exceptions.AuthenticationFailed('Not authenticated user!')

-class ProfileView(APIView):
+class ProfileView(generics.GenericAPIView):
  parser_classes = (MultiPartParser, FormParser)
+ serializer_class = ProfileSerializer
  def get(self, request):
   user = request.user
   if user.is_authenticated:
    profile = Profile.objects.get(user=user)
-   return Response(ProfileSerializer(profile).data)
+   serializer = self.get_serializer(profile)
+   return Response(serializer.data)
   else:
    raise exceptions.AuthenticationFailed('Not authenticated user!')

def get_serializer(self, *args, **kwargs):
    """
    Return the serializer instance that should be used for validating and
    deserializing input, and for serializing output.
    """
    serializer_class = self.get_serializer_class()
    kwargs['context'] = self.get_serializer_context()
    return serializer_class(*args, **kwargs)

def to_representation(self, value):
  if not value:
   return None
  use_url = getattr(self, 'use_url', api_settings.UPLOADED_FILES_USE_URL)
  if use_url:
   if not getattr(value, 'url', None):
    # If the file has not been saved it may not have a URL.
    return None
   url = value.url
   request = self.context.get('request', None)
   if request is not None:
    return request.build_absolute_uri(url)
   return url
  return value.name