1. There is no cascade delete after ForeignKey

Problems encountered:

File "H:\djangoProject\djangoProject\test\test7\stu\models.py", line 24, in Student
    cls = models.ForeignKey(Clazz)   # 连接班级表
TypeError: __init__() missing 1 required positional argument: 'on_delete'

Solution:

cls = models.ForeignKey(Clazz, on_delete=models.CASCADE)   #  级联删除别忘了加