# 出版社

class Publisher(models.Model):

    # 自增、主键 id

    id = models.AutoField(primary_key=True)

    # varchar(32)、不为空、唯一索引

    name = models.CharField(max_length=32, null=False, unique=True)

# 书

class Booker(models.Model):

    id = models.AutoField(primary_key=True)

    title = models.CharField(max_length=64, null=False, unique=True)

    publisher = models.ForeignKey(to="Publisher")

publisher = models.ForeignKey(to="Publisher", on_delete=models.CASCADE)

publisher = models.ForeignKey(to="Publisher", on_delete=models.CASCADE, default=1)