JPA的cascade = REMOVE和Hibernate的@OnDelete一起使用？ [英] JPA's cascade = REMOVE and Hibernate's @OnDelete used together?

问题描述

我继承了几乎所有关系都具有以下注释的代码库：

  @OneToMany（fetch = FetchType。 LAZY，cascade = {CascadeType.REMOVE}，mappedBy =someThing）
 @OnDelete（action = OnDeleteAction.CASCADE）
  

现在我无法理解 @OnDelete 是否首先执行的操作。 Hibernate：OnDelete vs cascade = CascadeType.REMOVE 很有趣，但不幸的是，没有任何答案，并且 @OnDelete 的JavaDoc特别没有价值。

从其他问题看，它看起来像OnDelete注释以某种方式让数据库执行级联，而 @OneToMany 上的级联指令让ORM执行它，但是将它们一起使用的目的是什么？ p>

并且 @OneToMany 的cascade指令真的不允许ORM实现生成基于数据库的级联呢？

解决方案

假设您有一对一的定向关系

  class House {
 
 @OneToOne 
对象门; 
 
 
 
 
 
 
 
如果你使用CascadeType.REMOVE，那么删除房子也会删除大门。
 
 
  @OneToOne（cascade = CascadeType.REMOVE）
对象门; 
  
如果您使用@O​​nDelete，那么删除大门也会删除房屋。
  @OneToOne 
 @OnDelete（action = OnDeleteAction.CASCADE）
对象门; 
  
在这里阅读更多： http://www.ninthavenue.com.au/jpa-cascadetype-remove-vs-hibernate-ondelete  
 
I have inherited a code base on which nearly all relations have the following annotations:
@OneToMany(fetch = FetchType.LAZY, cascade = { CascadeType.REMOVE }, mappedBy = "someThing")
@OnDelete(action = OnDeleteAction.CASCADE)
Now I'm having trouble understanding what @OnDelete does in the first place. Hibernate: OnDelete vs cascade=CascadeType.REMOVE is interesting, but unfortunately doesn't have any answers and the JavaDoc for @OnDelete is particularly worthless.

From the other questions it looks like the OnDelete annotation somehow lets the DB do the cascading, while the cascading directive on @OneToMany let's the ORM do it, but what would ever be the purpose of using them together?

And does @OneToMany's cascade directive really doesn't allow the ORM implementation to generate a DB based cascade anyway?
解决方案
Let's say you have a one-to-one directional relationship
class House {

    @OneToOne
    Object door;

}
If you use CascadeType.REMOVE then deleting the house will also delete the door.
    @OneToOne(cascade=CascadeType.REMOVE)
    Object door;
If you use @OnDelete then deleting the door will also delete the house.
    @OneToOne
    @OnDelete(action = OnDeleteAction.CASCADE)
    Object door;
Read more here: http://www.ninthavenue.com.au/jpa-cascadetype-remove-vs-hibernate-ondelete

                        
这篇关于JPA的cascade = REMOVE和Hibernate的@OnDelete一起使用？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！