new_contents: from rest_framework import validators
  from rest_framework.exceptions import ValidationError
  
  
  class UniqueTogetherValidator(validators.UniqueTogetherValidator):
      def __call__(self, attrs):
          self.enforce_required_fields(attrs)
          queryset = self.queryset
          queryset = self.filter_queryset(attrs, queryset)
          queryset = self.exclude_current_instance(attrs, queryset)
          if queryset.first():
              field_names = ', '.join(self.fields)
              raise ValidationError(self.message.format(field_names=field_names))
  
subject: Add validators.UniqueTogetherValidator