当我从数据库/模型中删除一个对象时，如果有两个类，如何让Django Admin删除文件？

from django.db import models

class ClassA(models.Model):
    # 模型字段定义
    pass

class ClassB(models.Model):
    class_a = models.ForeignKey(ClassA, on_delete=models.CASCADE)
    file = models.FileField(upload_to='files/')  # 文件字段定义

from django.contrib import admin
from .models import ClassA, ClassB

admin.site.register(ClassA)
admin.site.register(ClassB)

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

@receiver(pre_delete, sender=ClassA)
def delete_related_files(sender, instance, **kwargs):
    for obj in instance.classb_set.all():
        obj.file.delete()  # 删除关联的文件