Question

我有以下型号。

Book has Articles (Article has foreign key to Book)

Article has Images (Article has upto #max number of foreign keys to images, Article have #max number of foreign key to images. which maybe null)

Furthermore I have Book - Image relation 
because certain images are included in the book but not owned by article

我让模型快速回答诸如

之类的查询

给我一篇文章的图片。
给我一本书的图像（按时间排序，如果需要，可以分页）

人们建议我的模型不好。（when foreign key points to something else, move other data as well）

想要了解更好的替代架构。

Answer 1

我会选择（假设postgresql数据库）的简单解决方案：

create table book (
  id integer primary key
);

create table article (
  id integer primary key,
  id_book integer references book(id)
);

create table image (
  id integer primary key,
  id_article integer references article(id),
  id_book integer references book(id),
  check ((id_article is null or id_book is null) and
    (id_article is not null or id_book is not null))
);

检查约束不允许将图像分配给文章或书籍。

如果图片来自文章=＆gt; id_article已填写
如果仅限于书籍（不是来自文章）=＆gt; id_book已填写

给我一本书的图像

select *
from book b
left join 
 (select *, id_book as book from image where id_article is null 
  union all
  select i.*, a.id_book as book from article a join image i on i.id_article=a.id) i on i.book = b.id;

书籍的数据库架构建议 - 文章 - 图片

1 个答案: