如何用父表的值填充Django模型/表中的外键列？

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

@receiver(pre_save, sender=ParentModel)
def populate_foreign_key(sender, instance, **kwargs):
    # 获取父表的值
    parent_value = instance.parent_field

    # 将父表的值赋给外键列
    instance.child_model.foreign_key = parent_value

from django.db import models

class ParentModel(models.Model):
    # 父表字段定义

# 将信号处理函数与父表模型关联
pre_save.connect(populate_foreign_key, sender=ParentModel)