Django数据模型中on_delete使用详解

from django.db import models

class Manufacturer(models.Model):
  # ...
  pass

class Car(models.Model):
  manufacturer = models.ForeignKey(Manufacturer, on_delete=models.CASCADE)
  # ...

class ApiList(models.Model):
 desc = models.CharField(max_length=255, verbose_name="接口描述")
 keyword = models.CharField(max_length=100, verbose_name="请求关键字")
 response = models.TextField(verbose_name="响应结果")
 api = models.ForeignKey(Api, blank=True, null=True, on_delete=models.SET_NULL, verbose_name="所属接口")
 status = models.IntegerField(default=1, verbose_name="状态")
 create_at = models.CharField(max_length=20, verbose_name="创建时间")
 update_at = models.CharField(max_length=20, verbose_name="更新时间")

class ForeignKey(ForeignObject):
  def __init__(self, to, on_delete, related_name=None, related_query_name=None,
         limit_choices_to=None, parent_link=False, to_field=None,
         db_constraint=True, **kwargs):
    super().__init__(to, on_delete, from_fields=['self'], to_fields=[to_field], **kwargs)

class OneToOneField(ForeignKey):
  def __init__(self, to, on_delete, to_field=None, **kwargs):
    kwargs['unique'] = True
    super().__init__(to, on_delete, to_field=to_field, **kwargs)

on_delete=None,        # 删除关联表中的数据时,当前表与其关联的field的行为
on_delete=models.CASCADE,   # 删除关联数据,与之关联也删除
on_delete=models.DO_NOTHING, # 删除关联数据,什么也不做
on_delete=models.PROTECT,   # 删除关联数据,引发错误ProtectedError
# models.ForeignKey('关联表', on_delete=models.SET_NULL, blank=True, null=True)
on_delete=models.SET_NULL,  # 删除关联数据,与之关联的值设置为null（前提FK字段需要设置为可空,一对一同理）
# models.ForeignKey('关联表', on_delete=models.SET_DEFAULT, default='默认值')
on_delete=models.SET_DEFAULT, # 删除关联数据,与之关联的值设置为默认值（前提FK字段需要设置默认值,一对一同理）
on_delete=models.SET,     # 删除关联数据,
 a. 与之关联的值设置为指定值,设置：models.SET(值)
 b. 与之关联的值设置为可执行对象的返回值,设置：models.SET(可执行对象)

class ManyToManyField(RelatedField):
  def __init__(self, to, related_name=None, related_query_name=None,
         limit_choices_to=None, symmetrical=None, through=None,
         through_fields=None, db_constraint=True, db_table=None,
         swappable=True, **kwargs):
    super().__init__(**kwargs)