python - 如何在 django 模型中初始化与自身无关的 ManyToMany 字段(对象级别)？

Question

示例:

class MyUser(models.Model):
    blocked_users = models.ManyToManyField("self", blank=True, null=True)

user = MyUser.object.get(pk=1)
user.blocked_users.add(user)
user.blocked_users.all()[0] == user # (!!!)

可以在模型/数据库级别阻止它吗？或者我们只需要检查应用程序中的某个位置。

Answer 1

查看 Django 文档 ManyToManyField arguments ，看来不可能。

最接近您想要的参数是 limit_choices_to然而，那个only limits choices on ModelForms and admin (您仍然可以像在示例中那样保存它)，并且当前有 no easy way to use it to limit based on another value (pk) in the current model .

如果您想完全防止这种情况发生，您必须求助于 overriding the save method on the through model --类似:

class MyUser(models.Model):
    blocked_users = models.ManyToManyField(..., through="BlockedUser")

class BlockedUser(models.Model):
    user = models.ForeignKey(MyUser)
    blocked = models.ForeignKey(MyUser)

    def save(self, *args, **kwargs):
        # Only allow this relationship to be created if 
        if self.user != self.blocked:
            super(BlockedUser, self).save(*args, **kwargs)

您当然也可以使用signals来做到这一点.