休眠：安全地将对象重新连接到会话 [英] Hibernate: Safely reattach an object to the session

问题描述

通过在地图中存储（可能分离的）对象，我在整个hibernate会话中维护对象的缓存。当缓存命中时，我测试对象是否已经是 Session.contains（object）的会话的一部分。如果没有，我用 Session.lock（object，LockMode.NONE）重新附加它。

问题是，如果先前在会话中加载了相同的对象，则会引发org.hibernate.NonUniqueObjectException。给定一个分离的实例，我无法预先知道是否会抛出异常，而不会触及数据库。

有几个解决方法：

1. 在开始时重新附加所有缓存的对象的每笔交易。
   
2. 捕获NonUniqueObjectException，然后调用session.load（object.class，object.getId（））;
   

这些都不像提前为对象类+ id检查会话那样干净。

有没有办法做到这一点？

解决方案

Session.merge（）应该这样做：

  obj = session.merge（obj）; 
  

I'm maintaining a cache of objects across hibernate sessions by storing (possibly-detached) objects in a map. When the cache gets a hit, I test if the object is already part of the session with Session.contains(object). If not, I re-attach it with Session.lock(object, LockMode.NONE).

The problem is, if the same object was loaded previously in the session, it throws a org.hibernate.NonUniqueObjectException. Given a detached instance, I see no way to find out in advance if this exception will get thrown, without possibly hitting the database.

There are a couple workarounds:

1. Reattach all cached objects at the start of every transaction.
2. Catch the NonUniqueObjectException and then call session.load(object.class, object.getId());

Neither of these are as clean as checking the session in advance for an object class + id.

Is there any way to do that?

解决方案

Session.merge() should do it:

obj = session.merge(obj);

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