Hibernate中遇到的一个Exception

最新推荐文章于 2020-12-23 20:18:26 发布

转载最新推荐文章于 2020-12-23 20:18:26 发布 · 137 阅读

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原文链接：http://www.cnblogs.com/codingforum/p/4316865.html

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#java #数据库

本文详细解析了在使用Hibernate框架时遇到的关于ObjectVersion包含两个oneToMany关系导致的'Illegal attempt to associate a collection with two open sessions'错误的原因，并提供了正确的解决方法。通过将saveOrUpdate操作替换为merge操作，可以避免此类错误的发生。

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做项目的时候遇到一个很头疼的报错：Illegal attempt to associate a collection with two opensessions

出错原因: 一个Object Version 包含了两个oneTomany关系。在数据库调取出一个version对象时，再用saveOrUpdate这个对象就会出现如上错误

解决办法: 讲session.saveOrUpdate(version)改为session.merge(version)

原理分析: saveOrUpdate是在同一个session里用于保存或更新一个条目，而merge可以用于两个不同session数据的保存或更新。
HibernateReference里说：

saveOrUpdate() does the following:

if the object is already persistent in this session, donothing
if another object associated with the session has the sameidentifier, throw an exception
if the object has no identifier property, save() it
if the object's identifier has the value assigned to a newlyinstantiated object, save() it
if the object is versioned by a or , and the version property valueis the same value assigned to a newly instantiated object, save()it
otherwise update() the object

merge() is very different:

if there is a persistent instance with the same identifiercurrently associated with the session, copy the state of the givenobject onto the persistent instance
if there is no persistent instance currently associated with thesession, try to load it from the database, or create a newpersistent instance
the persistent instance is returned
the given instance does not become associated with the session, itremains detached

网上有其他资料说代码如下：entity=merge(entity); saveOrUpdate(entity);这是错误的，第二行代码完全没有必要，因为entity已经是persistentobject，会被saveOrUpdate忽略。直接用session.merge（version)即可。

转载于:https://www.cnblogs.com/codingforum/p/4316865.html