Django外键访问save()函数

这是我的代码:

class Publisher(models.Model):
    name = models.CharField(
            max_length = 200,
            unique = True,
    )

    url = models.URLField()

    def __unicode__(self):
        return self.name

    def save(self):
        pass

class Item(models.Model):
    publisher = models.ForeignKey(Publisher)

    name = models.CharField(
            max_length = 200,
    )

    code = models.CharField(
            max_length = 10,
    )

    def __unicode__(self):
        return self.name

def save(self, **kwargs):
    super(Publisher, self).save(**kwargs)

    for item in self.item_set.all():
        item.code = "%s - whatever" % item.code