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POHibernate: comparing current & previous record
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copied!<p>I want to compare the current value of an in-memory Hibernate entity with the value in the database:</p> <pre><code>HibernateSession sess = HibernateSessionFactory.getSession(); MyEntity newEntity = (MyEntity)sess.load(MyEntity.class, id); newEntity.setProperty("new value"); MyEntity oldEntity = (MyEntity)sess.load(MyEntity.class, id); // CODEBLOCK#1 evaluate differences between newEntity and oldEntity sess.update(newEntity); </code></pre> <p>In <strong>CODEBLOCK#1</strong> I get that <code>newEntity.getProperty()="new value"</code> AND <code>oldEntity.getProperty()="new value"</code> (while I expected <code>oldEntity.getProperty()="old value"</code>, of course). In fact the two objects are exactly the same in memory.</p> <p>I messed around with <code>HibernateSessionFactory.getSession().evict(newEntity)</code> and attempted to set <code>oldEntity=null</code> to get rid of it (I need it only for the comparison):</p> <pre><code>HibernateSession sess = HibernateSessionFactory.getSession(); MyEntity newEntity = (MyEntity)sess.load(MyEntity.class, id); newEntity.setProperty("new value"); HibernateSessionFactory.getSession().evict(newEntity); MyEntity oldEntity = (MyEntity)sess.load(MyEntity.class, id); // CODEBLOCK#1 evaluate differences between newEntity and oldEntity oldEntity = null; sess.update(newEntity); </code></pre> <p>and now the two entities are distinct, but of course I get the dreaded <code>org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session</code>.</p> <p>Any idea?</p> <p><strong>EDIT:</strong> I tried the double session strategy; I modified my <code>HibernateSessionFactory</code> to implement a map of session and then...</p> <pre><code>Session session1 = HibernateSessionFactory.getSession(SessionKeys.DEFAULT); Session session2 = HibernateSessionFactory.getSession(SessionKeys.ALTERNATE); Entity newEntity = (Entity)entity; newEntity.setNote("edited note"); Entity oldEntity = (Entity)session1.load(Entity.class, id); System.out.println("NEW:" + newEntity.getNote()); System.out.println("OLD: " + oldEntity.getNote()); // HANGS HERE!!! HibernateSessionFactory.closeSession(SessionKeys.ALTERNATE); </code></pre> <p>My unit test hangs while attempting to print the oldEntity note... :-(</p>

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