java Hibernate：安全地将对象重新附加到会话
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Hibernate: Safely reattach an object to the session
提问by Rob
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).
我通过在地图中存储（可能分离的）对象来维护跨休眠会话的对象缓存。当缓存命中时，我测试对象是否已经是会话的一部分Session.contains(object)。如果没有，我用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.
问题是，如果先前在会话中加载了相同的对象，则会抛出 org.hibernate.NonUniqueObjectException。给定一个分离的实例，我看不出有没有办法提前知道这个异常是否会被抛出，而不可能访问数据库。
There are a couple workarounds:
有几种解决方法：
- Reattach all cached objects at the start of every transaction.
- Catch the NonUniqueObjectException and then call session.load(object.class, object.getId());
- 在每个事务开始时重新附加所有缓存的对象。
- 捕获 NonUniqueObjectException 然后调用 session.load(object.class, object.getId());
Neither of these are as clean as checking the session in advance for an object class + id.
这些都不像提前检查会话中的对象类 + id 那样干净。
Is there any way to do that?
有没有办法做到这一点？
回答by Raj
Session.merge() should do it:
Session.merge() 应该这样做：
obj = session.merge(obj);
回答by Pascal Thivent
I'm maintaining a cache of objects across hibernate sessions
我正在跨休眠会话维护对象缓存
Not a direct answer but why don't you use Hibernate L2 cache for this instead of reinventing the wheel?
不是直接的答案，但为什么不为此使用 Hibernate L2 缓存而不是重新发明轮子呢？
