在Django中清除时如何更改另一个字段值？

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

from django.db import models

class MyModel(models.Model):
    field1 = models.CharField(max_length=100)
    field2 = models.CharField(max_length=100)

@receiver(pre_delete, sender=MyModel)
def update_field2(sender, instance, **kwargs):
    instance.field2 = "新的值"
    instance.save()

from django.apps import AppConfig

class MyAppConfig(AppConfig):
    default_auto_field = 'django.db.models.BigAutoField'
    name = 'myapp'

    def ready(self):
        import myapp.signals  # 导入信号模块