      def build_relational_field(self, field_name, relation_info):
          """
          Create fields for forward and reverse relationships.
          """
          field_class = self.serializer_related_class
          field_kwargs = get_relation_kwargs(field_name, relation_info)
  
          # `view_name` is only valid for hyperlinked relationships.
          if not issubclass(field_class, HyperlinkedRelatedField):
              field_kwargs.pop('view_name', None)
 
</s> remove         field_class = HyperlinkedIdentityField
 </s> add         field_class = self.serializer_url_field </s> remove             field_class = ChoiceField
 </s> add             field_class = self.serializer_choice_field </s> remove     serializer_related_class = PrimaryKeyRelatedField
 </s> add     serializer_related_field = PrimaryKeyRelatedField
    serializer_url_field = HyperlinkedIdentityField
    serializer_choice_field = ChoiceField </s> remove     serializer_related_class = HyperlinkedRelatedField
 </s> add     serializer_related_field = HyperlinkedRelatedField
        field_class = self.serializer_related_field
      def build_relational_field(self, field_name, relation_info):
          """
          Create fields for forward and reverse relationships.
          """
        field_class = self.serializer_related_field
          field_kwargs = get_relation_kwargs(field_name, relation_info)
  
          # `view_name` is only valid for hyperlinked relationships.
          if not issubclass(field_class, HyperlinkedRelatedField):
              field_kwargs.pop('view_name', None)
keep keep keep keep replace keep keep keep keep keep
 Minor cleanups/improvements to ModelSerializer API 
rest_framework/serializers.py