Question

class Piece(models.Model):
    pass

class Article(Piece):
    article_piece = models.OneToOneField(Piece, on_delete=models.CASCADE, parent_link=True)
    ...

class Book(Piece):
    book_piece = models.OneToOneField(Piece, on_delete=models.CASCADE, parent_link=True)
    ...

class BookReview(Book, Article):
    pass

我正在查看一些文档，它说上述代码可用于为BookReview提供其他字段和方法，而不会发生任何冲突我收到错误You are trying to add a non-nullable field 'article_piece' to article without a default; we can't do that (the database needs something to populate existing rows). Please select a fix: 1) Provide a one-off default now (will be set on all existing rows with a null value for this column) 2) Quit, and let me add a default in models.py Select an option: 2

实例化BookReview时，默认值是什么？我将使用article_piece，book_piece的哪个实例？

Answer 1

此消息显示您为Article模型所用，没有指定字段article_piece可能是数据库中的NULL。因此，Django要求您提供默认值（基本上将任何Piece记录分配给该字段）或由您自己管理。

如果不希望出现此情况，则只需将该字段设置为空即可（也可以为空，这样表格就不需要此字段了）：

article_piece = models.OneToOneField(Piece, blank=True, null=True, on_delete=models.CASCADE, parent_link=True)

Django多重继承避免方法冲突

1 个答案: