如何在Django中为每个所有者(ForeignKey)增加"number“字段

from django.db import models

class Owner(models.Model):
    name = models.CharField(max_length=100)

class OwnedItem(models.Model):
    owner = models.ForeignKey(Owner, on_delete=models.CASCADE)
    number = models.PositiveIntegerField()
    # 其他字段...

class OwnedItemManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().order_by('owner', 'number')

class OwnedItem(models.Model):
    owner = models.ForeignKey(Owner, on_delete=models.CASCADE)
    number = models.PositiveIntegerField()
    # 其他字段...

    objects = OwnedItemManager()

from django.db.models.signals import pre_save
from django.dispatch import receiver

@receiver(pre_save, sender=OwnedItem)
def assign_number(sender, instance, **kwargs):
    if not instance.pk:  # 只有在创建新实例时才分配编号
        last_item = OwnedItem.objects.filter(owner=instance.owner).order_by('-number').first()
        instance.number = (last_item.number if last_item else 0) + 1

from django.apps import AppConfig

class YourAppConfig(AppConfig):
    name = 'your_app'

    def ready(self):
        import your_app.models  # 导入模型以启用信号

default_app_config = 'your_app.apps.YourAppConfig'