java - hibernate envers : merge & saveOrUpdate

Question

我正在开发一个 spring-hibernate-envers 应用程序。经过大量谷歌搜索，事情终于对我有用了，但我仍然有几个问题。

1. 早些时候我使用saveOrUpdate 保存或更新实体。但 与envers一起工作时 抛出一个 nonUniqueObject 异常(exception)。所以我改用 merge 它奏效了。使用是否正确 为此合并？ merge 是否插入 数据库的新对象？

2. 我尝试了以下代码:

entity=merge(entity);  
saveOrUpdate(entity);

这也奏效了。这是正确的方法吗？而且我很好奇为什么 saveOrUpdate 现在没有抛出任何错误。

Answer 1

Hibernate Reference说:

saveOrUpdate() does the following:

• if the object is already persistent in this session, do nothing
• if another object associated with the session has the same identifier, throw an exception
• if the object has no identifier property, save() it
• if the object's identifier has the value assigned to a newly instantiated object, save() it
• if the object is versioned by a or , and the version property value is the same value assigned to a newly instantiated object, save() it
• otherwise update() the object

and merge() is very different:

• if there is a persistent instance with the same identifier currently associated with the session, copy the state of the given object onto the persistent instance
• if there is no persistent instance currently associated with the session, try to load it from the database, or create a new persistent instance
• the persistent instance is returned
• the given instance does not become associated with the session, it remains detached

这意味着如果您确定具有相同标识符的对象未与 session 相关联，则可以使用saveOrUpdate()。否则你应该使用 merge()。

下面的代码

entity=merge(entity);
saveOrUpdate(entity); 

之所以有效，是因为 merge() 的结果是一个持久对象，因此它会被 saveOrUpdate() 忽略，因此第二行没有任何意义。