Django2.0之后使用外键时遇到 __init__() missing 1 required positional argument: 'on_delete'

1.Django2.0之后使用外键时遇到

__init__() missing 1 required positional argument: 'on_delete'

需要在外键创建时给on_delete参数赋值。models.CASCADE是老版本的默认值。

publish = models.ForeignKey("Publish", on_delete=models.CASCADE)