教义一对多没有加入表

Question

我正在使用Doctrine，我想知道如果不使用连接表，我是否可以拥有一对多的关系？

Answer 1

Depends on whether you want it to be unidirectional or bidirectional.

Unidirectional one-to-many can be made only through join table, for "ideological" reasons, which came from Java's hibernate:

http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/reference/association-mapping.html#one-to-many-unidirectional-with-join-table

Imagine you have a Category which has many Products, and you want a unidirectional relationship - ie category knows about many products, but products don't know about category.

If you put a 'category_id' field into Product table, you will make product table "aware" of the fact that it is connected to category. And you will not be able to remove this relationship without altering Product table - that means it is not truly unidirectional.

But if you keep relationship between category and products in the separate join table, you can just drop it and Product won't even notice that something has changed.

Answer 2

只有m：n关系才需要连接表。