I've got this Serializer translating path to url, and it works on its own, but when i try to nest this serializer inside another serializer, i get this error. Do you have any idea why? I need to have this function, because otherwise it just shows the paths to the image in this main SpecialistSerializer.

class EntityPhotosSerializer(serializers.ModelSerializer):
    image = serializers.SerializerMethodField('get_file_abs_url')


    class Meta:
        model = EntityPhoto
        fields = ('user', 'entity', 'image',)

    def get_file_abs_url(self, obj):
        request = self.context.get('request')
        return request.build_absolute_uri(obj.image.url)

class SpecialistSerializer(serializers.ModelSerializer):
    reviews_quantity = serializers.IntegerField(source="get_reviews_quantity")

    class Meta:
        model = Entity
        fields = '__all__'

    def to_representation(self, instance):
        data = super().to_representation(instance)
        data['photos'] = EntityPhotosSerializer(many=True, instance=instance.entityphoto_set.all()).data
        return data

Traceback:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/core/handlers/base.py", line 179, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/views/generic/base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
    raise exc
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/generics.py", line 282, in get
    return self.retrieve(request, *args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/mixins.py", line 56, in retrieve
    return Response(serializer.data)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/serializers.py", line 548, in data
    ret = super().data
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/serializers.py", line 246, in data
    self._data = self.to_representation(self.instance)
  File "/Users/jakubstrawa/programming/PythonKuba/api/specialists/serializers.py", line 35, in to_representation
    data['photos'] = EntityPhotosSerializer(many=True, instance=instance.entityphoto_set.all()).data
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/serializers.py", line 745, in data
    ret = super().data
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/serializers.py", line 246, in data
    self._data = self.to_representation(self.instance)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/serializers.py", line 664, in to_representation
    self.child.to_representation(item) for item in iterable
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/serializers.py", line 664, in <listcomp>
    self.child.to_representation(item) for item in iterable
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/serializers.py", line 515, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/rest_framework/fields.py", line 1870, in to_representation
    return method(value)
  File "/Users/jakubstrawa/programming/PythonKuba/api/specialists/serializers.py", line 23, in get_file_abs_url
    return request.build_absolute_uri(obj.image.url)
AttributeError: 'NoneType' object has no attribute 'build_absolute_uri'

CodePudding user response：

In to_representation, you access to the EntityPhotosSerializer. And in that serializer, you are trying to access to the context. If you want to do that, you need to pass the current context to EntityPhotosSerializer in SpecialistSerializer.

    def to_representation(self, instance):
        data = super().to_representation(instance)
        data['photos'] = EntityPhotosSerializer(many=True, context=self.context, instance=instance.entityphoto_set.all()).data
        return data