to_representation error：'NoneType'對象不可迭代

Question

我試圖更新DRF transform_<name>以使用新的to_representation方法。當我嘗試這樣做時，我收到以下錯誤，我很難追查。我已在所有串行測試這一點，我得到同樣的事情：

Traceback (most recent call last): 
    File "/Users/glyn/Documents/workspace/app/django-env/lib/python2.7/site-packages/django/core/handlers/base.py", line 111, in get_response 
    response = wrapped_callback(request, *callback_args, **callback_kwargs) 
    File "/Users/glyn/Documents/workspace/app/django-env/lib/python2.7/site-packages/django/views/decorators/csrf.py", line 57, in wrapped_view 
    return view_func(*args, **kwargs) 
    File "/Users/glyn/Documents/workspace/app/django-env/lib/python2.7/site-packages/django/views/generic/base.py", line 69, in view 
    return self.dispatch(request, *args, **kwargs) 
    File "/Users/glyn/Documents/workspace/app/django-env/lib/python2.7/site-packages/rest_framework/views.py", line 407, in dispatch 
    response = self.handle_exception(exc) 
    File "/Users/glyn/Documents/workspace/app/django-env/lib/python2.7/site-packages/rest_framework/views.py", line 404, in dispatch 
    response = handler(request, *args, **kwargs) 
    File "/Users/glyn/Documents/workspace/app/app/apps/ornamentation/views/photo.py", line 23, in get 
    return self.retrieve(request, *args, **kwargs) 
    File "/Users/glyn/Documents/workspace/app/django-env/lib/python2.7/site-packages/rest_framework/mixins.py", line 56, in retrieve 
    return Response(serializer.data) 
    File "/Users/glyn/Documents/workspace/app/django-env/lib/python2.7/site-packages/rest_framework/serializers.py", line 464, in data 
    return ReturnDict(ret, serializer=self) 
    File "/Users/glyn/Documents/workspace/app/django-env/lib/python2.7/site-packages/rest_framework/utils/serializer_helpers.py", line 14, in __init__ 
    super(ReturnDict, self).__init__(*args, **kwargs) 
    File "/usr/local/Cellar/python/2.7.8_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/collections.py", line 52, in __init__ 
    self.__update(*args, **kwds) 
    File "/Users/glyn/Documents/workspace/app/django-env/bin/../lib/python2.7/_abcoll.py", line 566, in update 
    for key, value in other: 
TypeError: 'NoneType' object is not iterable 

我的代碼：

class ThumbnailSerializerMixin(serializers.HyperlinkedModelSerializer): 
    """ 
    Mixin used to create a thumbnail based on parameters. 
    If no parameters have been passed defaults are used. 
    """ 

    thumbnail_image = HyperlinkedImageField() 
    thumbnail = HyperlinkedImageField() 


    def to_representation(self, instance): 
      super(PhotoThumbnailSerializer,self).to_representation(instance) 

    def transform_thumbnail(self, obj, value): 
     """ 
     :param: thumbnail_width, thumbnail_height, thumbnail_quality, 
     :return: S3 signed URL to thumbnail. 
     """ 

     if not value == "null": 
      width = self.context['request'].GET.get('thumbnail_width', settings.THUMBNAIL_DEFAULT_WIDTH) 
      height = self.context['request'].GET.get('thumbnail_height', settings.THUMBNAIL_DEFAULT_HEIGHT) 
      quality = self.context['request'].GET.get('thumbnail_quality', settings.THUMBNAIL_DEFAULT_QUALITY) 
      return urllib.quote(obj.thumbnail(width=width, height=height, quality=quality).url, safe="%/:=&?~#+!$,;'@()*[]") 
     return "null" 

    class Meta: 
     abstract = True 
     fields = ("url", "thumbnail_image", "thumbnail",) 


    class PhotoThumbnailSerializer(ThumbnailSerializerMixin): 
     url = serializers.HyperlinkedIdentityField(view_name='photo_detail') 
     raw_image = HyperlinkedImageField() 

     class Meta(ThumbnailSerializerMixin.Meta): 
      model = Photo 
      fields = ("url", "raw_image", "thumbnail",) 

注：上面我已經離開在transform_thumbnail這是我的老方法。在to_representation方法中添加會生成錯誤。

Answer 1

你的to_representation方法不能返回空值。你忘記了return聲明。

def to_representation(self, instance): 
    return super(PhotoThumbnailSerializer,self).to_representation(instance)