Hibernate: compare current and previous record

Question

I want to compare the current value of the sleeping entity in memory with the value in the database:

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);    

In CODEBLOCK # 1, I get this newEntity.getProperty()="new value"AND oldEntity.getProperty()="new value"(although I expected oldEntity.getProperty()="old value", of course). In fact, both objects in memory are the same.

I mixed up with HibernateSessionFactory.getSession().evict(newEntity)and tried to install oldEntity=nullin order to get rid of it (I need this just for comparison):

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);

and now these two objects are different, but of course I get scary org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session.

Any idea?

EDIT: I tried a dual session strategy; I changed mine HibernateSessionFactoryto implement a session map, and then ...

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);

My unit test freezes when I try to print the note oldEntity ...: - (

Answer 1

spring:

• oldEntity newEntity
• session.merge() oldEntity (newEntity) (oldEntity)

: , , Hibernate , , . update() ( ), . :

HibernateSession sess = ...;
MyEntity oldEntity = (MyEntity) sess.load(...);
sess.evict(oldEntity); // old is now not in the session persistence context
MyEntity newEntity = (MyEntity) sess.load(...); // new is the only one in the context now
newEntity.setProperty("new value");
// Evaluate differences
sess.update(newEntity); // saving the one that in the context anyway = fine

:

HibernateSession sess = ...;
MyEntity newEntity = (MyEntity) sess.load(...);
newEntity.setProperty("new value");
sess.evict(newEntity); // otherwise load() will return the same object again from the context
MyEntity oldEntity = (MyEntity) sess.load(...); // fresh copy into the context
sess.merge(newEntity); // replaces old in the context with this one

Answer 2

session.isDirty()? JavaDoc , " - SQL , ?" , , . - .