1、ForeignKey后面未加级联删除

遇到的问题：

File "H:djangoProjectdjangoProject	est	est7stumodels.py", line 24, in Student
    cls = models.ForeignKey(Clazz)   # 连接班级表
TypeError: __init__() missing 1 required positional argument: 'on_delete'

解决办法：

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