def save_base(self, *args, **kwargs):
        """
        Update last_used of the used tag, whenever it is used in a
        save-operation.
        """
        self.tag.last_used = timezone.now()
        self.tag.save()
        return super().save_base(*args, **kwargs)

        Update last_used of the used tag, whenever it is used in a
        save-operation.
        
core/models.py