django cascade on related change foreign key

models.py

class CascadeOnRelatedChangeForeignKey(models.ForeignKey):
    """
    ForeignKey that deletes all instances of the "related_name"
    whenever the related instance changes.
    For example while using this field in a token model, if the user
    changes, all the tokens will be deleted.
    """

    def contribute_to_related_class(self, cls, related):
        from django.db.models.signals import post_save
        from django.dispatch import receiver

        related_name = related.get_accessor_name()

        @receiver(post_save, sender=cls)
        def on_user_change(sender, instance, created, **kwargs):
            if not created:
                getattr(instance, related_name).all().delete()

        super().contribute_to_related_class(cls, related)


class Token(AbstractToken):
    objects = TokenManager()

    user = CascadeOnRelatedChangeForeignKey(
        User,
        on_delete=models.CASCADE,
        related_name="tokens",
    )