django - 'unique_together' 指的是不存在的字段

Question

当尝试在两个外键约束上使用 unique_together 时，出现以下错误:

CommandError: System check identified some issues:

ERRORS:
main.AuthorTag: (models.E012) 'unique_together' refers to the non-existent field 'author'.
main.AuthorTag: (models.E012) 'unique_together' refers to the non-existent field 'tag'.

如下表

class AuthorTag(models.Model):
    class Meta:
        unique_together = (('tag', 'author',),)
    tag = models.ForeignKey(TagIndex, on_delete=models.CASCADE),
    author = models.ForeignKey(Author, on_delete=models.CASCADE),

同样的例子似乎在这里工作:Unique foreign key pairs with Django但我不明白为什么会出现这个错误

编辑:将 unique_together = (('tag', 'author',),) 更改为 unique_together = (('tag', 'author')) 给我同样的错误。以及将元类移至字段声明下方。

Answer 1

删除结尾的逗号，使代码:

class AuthorTag(models.Model):
    class Meta:
        unique_together = ['tag', 'author']

    tag = models.ForeignKey(TagIndex, on_delete=models.CASCADE)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)

成功了。我不确定为什么。