Django 模型在添加之前验证 ManyToMany 字段

Question

我有一个看起来有点像这样的模型:

class Passenger(models.Model):
    name = models.CharField(max_length=50)
    surname = models.CharField(max_length=50)


class Flight(models.Model):
    capacity = models.IntegerField()
    passengers = models.ManyToManyField(Passenger)

在向航类添加新乘客之前，我想验证乘客数量是否不会超过容量。我想知道什么是最好的方法来解决这个问题。

显然我可以在添加新乘客之前手动检查乘客数量，但也许 django 有一些支持？我尝试编写验证器，但不知道该怎么做。

Answer 1

根据姜戈 docs您可以收听 m2m_changed 信号，将触发 pre_add 和 post_add 行动。

Using add() with a many-to-many relationship, however, will not call any save() methods (the bulk argument doesn’t exist), but rather create the relationships using QuerySet.bulk_create(). If you need to execute some custom logic when a relationship is created, listen to the m2m_changed signal, which will trigger pre_add and post_add actions.