Hibernate中的 NonUniqueObjectException 及其解决之道

<P>近日遇到了NonUniqueObjectException错误，解决如下：<BR>org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session:<BR>a different object with the same identifier value was already associated with the session</P>
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<P>说你在现有的Session中已经绑定了一个对象，而这时，你还要强行将已经持久化的对象再重新加入到Session中。 <BR>在一个集合中的对象，随着一对多的中一的Load而级联Load进来，这时你的另一个持久化过的对象又想利用update()，会报这个错误。 <BR>又或者当你用session.lock()时，也可能。 <BR>总而言之，在你的Session中，已经存在（你想要更新的）对象了。</P>
<P>下面是Hibernate FAQ上的解释：</P>
<P>I called saveOrUpdate() or update() and got a NonUniqueObjectException! </P>
<P>The session maintains a unique mapping between persistent identity and object instance, in order to help you avoid data aliasing problems. You cannot simultaneously attach two objects with the same class and identifier to the same session. </P>
<P>The best way to avoid any possibility of this exception is to always call saveOrUpdate() at the beginning of the transaction, when the session is empty. </P>
<P>In Hibernate3, you can try using the merge() operation, which does not reattach the passed instance. <BR></P>