old_contents: from rest_framework import serializers
  
  from service.authors.serializers import SimpleAuthorSerializer
  from service.comments.serializers import CommentSerializer
  from social.app.models.post import Post
  
  
  class PostSerializer(serializers.HyperlinkedModelSerializer):
      # Not required by the spec, but makes testing a little easier
      url = serializers.HyperlinkedIdentityField(
          view_name="service:post-detail",
          source='id'
      )
      author = SimpleAuthorSerializer()
      comments = CommentSerializer(many=True)
  
      contentType = serializers.CharField(source="content_type", read_only=True)
  
      visibleTo = serializers.HyperlinkedRelatedField(
          many=True,
          read_only=True,
          source="visible_to",
          view_name="service:author-detail",
          lookup_field="pk"
      )
  
      categories = serializers.ListField(
          source="categories_list",
          read_only=True
      )
  
      class Meta:
          model = Post
          fields = ("title", "source", "origin", "description", "contentType", "content", "author",
                    "categories", "comments", "published", "id", "url", "visibility", "visibleTo",
                    "unlisted")
  
new_contents: from rest_framework import serializers
  
  from service.authors.serializers import SimpleAuthorSerializer
  from service.comments.serializers import CommentSerializer
  from social.app.models.post import Post
  
  
  class PostSerializer(serializers.HyperlinkedModelSerializer):
      # Not required by the spec, but makes testing a little easier
      url = serializers.HyperlinkedIdentityField(
          view_name="service:post-detail",
          source='id'
      )
      author = SimpleAuthorSerializer()
      comments = CommentSerializer(many=True)
  
      contentType = serializers.CharField(source="content_type", read_only=True)
  
      visibleTo = serializers.HyperlinkedRelatedField(
          many=True,
          read_only=True,
          source="visible_to_author",
          view_name="service:author-detail",
          lookup_field="pk"
      )
  
      categories = serializers.ListField(
          source="categories_list",
          read_only=True
      )
  
      class Meta:
          model = Post
          fields = ("title", "source", "origin", "description", "contentType", "content", "author",
                    "categories", "comments", "published", "id", "url", "visibility", "visibleTo",
                    "unlisted")
  
subject: Update visible_to reference to visible_to_author