Set the initial ordering value.

def save(self, *args, **kwargs):
        """
        Set the initial ordering value.
        """
        if self._order is None:
            lookup = self.with_respect_to()
            lookup["_order__isnull"] = False
            concrete_model = base_concrete_model(Orderable, self)
            self._order = concrete_model.objects.filter(**lookup).count()
        super(Orderable, self).save(*args, **kwargs)