为什么加了on_delete=models.CASCADE还是报错？

class Grade(models.Model):
g_name = models.CharField(max_length=10)

class Meta:
    db_table = 'grade'

class Student(models.Model):
s_name = models.CharField(max_length=10,unique=True)
s_age = models.IntegerField(default=16)
s_sex = models.BooleanField(default=1)
operator_time = models.DateTimeField(auto_now=True)
create_time = models.DateTimeField(auto_now=True,null=True)
g = models.ForeignKey(Grade,on_delete=models.CASCADE)
class Meta:
db_table = 'student'

报错TypeError: init() missing 1 required positional argument: 'on_delete'

是不是数据库同步出问题了