Django REST Framework and FileField absolute url

Try SerializerMethodField

Example (untested):

class MySerializer(serializers.ModelSerializer):
    thumbnail_url = serializers.SerializerMethodField('get_thumbnail_url')

    def get_thumbnail_url(self, obj):
        return self.context['request'].build_absolute_uri(obj.thumbnail_url)

The request must available to the serializer, so it can build the full absolute URL for you. One way is to explicitly pass it in when the serializer is created, similar to this:

serializer = MySerializer(account, context={'request': request})