          opts = get_concrete_model(cls)._meta
          exclusions = [field.name for field in opts.fields + opts.many_to_many]
          for field_name, field in self.fields.items():
              field_name = field.source or field_name
              if field_name in exclusions and not field.read_only:
                  exclusions.remove(field_name)
          return exclusions
  
      def full_clean(self, instance):
          """
 
</s> remove                 if related is None:
                    previous = getattr(obj, accessor_name, related)
                    if previous:
                        previous.delete()
                elif isinstance(related, models.Model):
 </s> add                 field = self.fields.get(accessor_name, None)
                if isinstance(field, Serializer):
                    # TODO: Following will be needed for reverse FK
                    # if field.many:
                    #     # Nested reverse fk relationship
                    #     for related_item in related:
                    #         fk_field = obj._meta.get_field_by_name(accessor_name)[0].field.name
                    #         setattr(related_item, fk_field, obj)
                    #         self.save_object(related_item)
                    # else:
                    # Nested reverse one-one relationship </s> remove     class Meta:
        model = OneToOneTarget
 </s> add             class Meta:
                model = OneToOneTarget
                fields = ('id', 'name', 'source')
            if field_name in exclusions \
                and not field.read_only \
                and not isinstance(field, Serializer):
          opts = get_concrete_model(cls)._meta
          exclusions = [field.name for field in opts.fields + opts.many_to_many]
          for field_name, field in self.fields.items():
              field_name = field.source or field_name
            if field_name in exclusions \
                and not field.read_only \
                and not isinstance(field, Serializer):
                  exclusions.remove(field_name)
          return exclusions
  
      def full_clean(self, instance):
          """
keep keep keep keep replace keep keep keep keep keep
 Cleanup one-one nested tests and implementation 
rest_framework/serializers.py