在 Django 中删除子对象时删除父对象

Question

class A(models.Model):
    name = models.CharField(max_length=128)

class B(modes.Model):
    type_b = models.ForeignKey(A)

In a one-to-many relationship in Django, how do I delete the "one" object (model 'A') when I delete one of the related "many" objects (model 'B')? I'm deleting the model 'B' object through the Django admin bulk delete option.

Answer 1

You should usesignals .

@receiver(post_delete, sender=B)
def delete_a(sender, instance, **kwargs):
     # instance.type_b is the object which you want to delete

Answer 2

A best way to do it, just add [on_delete=models.CASCADE][1]

:

class A(models.Model):
    name = models.CharField(max_length=128)

class B(modes.Model):
    type_b = models.ForeignKey(A,on_delete=models.CASCADE)

Answer 3

You can use post_delete signal to delete the parent as suggested by Davit Tovmasyan.

BUT because of the cascading nature as the parent A object is deleted, it will also delete all the connected B objects which will inturn emit post_delete signal on B model. So on the second emit of post_delete the signal handler tries to delete an already deleted item which causes 'NoneType' object has no attribute 'delete' . You can use exception handler or just use the if condition to handle this.

def delete_parent(sender, instance, **kwargs):
    if instance.type_b:
        instance.type_b.delete()

post_delete.connect(delete_parent, sender=B)