JPA orphanRemoval = true与ON DELETE CASCADE DML子句有何不同 [英] How does JPA orphanRemoval=true differ from the ON DELETE CASCADE DML clause

问题描述

我对JPA 2.0 orphanRemoval属性有些困惑.

I am a little confused about the JPA 2.0 orphanRemoval attribute.

我认为当我使用JPA提供程序的数据库生成工具来创建基础数据库DDL以在特定关系上具有ON DELETE CASCADE时，这是必需的.

I think I can see it is needed when I use my JPA provider's DB generation tools to create the underlying database DDL to have an ON DELETE CASCADE on the particular relation.

但是，如果数据库存在并且已经在关系上具有ON DELETE CASCADE，这是否不足以适当地级联删除? orphanRemoval还要做什么?

However, if the DB exists and it already has an ON DELETE CASCADE on the relation, is this not enough to cascade the deletion appropriately? What does the orphanRemoval do in addition?

欢呼

推荐答案

orphanRemoval与ON DELETE CASCADE无关.

orphanRemoval是完全 ORM特定的东西.当不再从父"实体中引用子"实体时，它会将其删除.当您从父实体的相应集合中删除子实体时.

orphanRemoval is an entirely ORM-specific thing. It marks "child" entity to be removed when it's no longer referenced from the "parent" entity, e.g. when you remove the child entity from the corresponding collection of the parent entity.

ON DELETE CASCADE是特定于数据库的事物，当删除父"行时，它将删除数据库中的子"行.

ON DELETE CASCADE is a database-specific thing, it deletes the "child" row in the database when the "parent" row is deleted.

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