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20 mai 2011 5 20 /05 /mai /2011 13:27



Why a NonUniqueObjectException is thrown ? 


A NonUniqueObjetException is thrown because hibernate is not able to decide what version of an entity it has to persist.


In this case, it will throw something like this :

org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [com.davidgimelle.hibernate.examples.Role#1]

at org.hibernate.engine.StatefulPersistenceContext.checkUniqueness(StatefulPersistenceContext.java:590)

at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performUpdate(DefaultSaveOrUpdateEventListener.java:284)

at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsDetached(DefaultSaveOrUpdateEventListener.java:223)

at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:89)

at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)

at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:507)

at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:499)

at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:495)

at com.davidgimelle.hibernate.examples.TestLostSession.commitADetachedObjetThrowAnNonUniqueObjectException(TestLostSession.java:53)

This exception has been thrown because hibernate has tried to persist 2 instances of the same entity, with the same id but not the same content.

For example : role1(id:1, name:"admin") and role2(id:1,name"user")


Usually that happens when an entity is persisted and detached from the session. Another instance of this entity is requested to hibernate. This second instance stayed attached to the session. The first instance is modified.


When hibernate persit the second instance, it is not able to choose what is the correct content to persist and throw an NonUniqueObjectException. 


It easier to understand with an example. This piece of code will throw and display an NonUniqueObjectException :


Role role = new Role().withName("Customer");


 //Persist a first Role Entity and close the session

Session openSession = sessionFactory.openSession();

Transaction beginTransaction = openSession.beginTransaction();




 //Now role is detached from the session


 //change a value in this role

role.setName("new role Name");


 //Open a new session

openSession =sessionFactory.openSession();


 //Instanciation of the same role from the new session

Role roleFromDB= (Role) openSession.get(Role.class, role.getId());

 //Now role and roleFromDB have the same id, but role is detached


Transaction beginTransaction2 = openSession.beginTransaction();



 //The next line will throw an exception


 //Save role and throw an exception



//This line will be never executed


Assert.fail();// Fail this test if this line is reached


catch(NonUniqueObjectException nuoe){

//Display this exception





You can find a complet maven project able to run this exemple in a Junit test at http://www.davidgimelle.com/src/hibernate_examples_dg-src.1.1.1-SNAPSHOT.zip 



- SaveOrUpdate versus Merge : http://www.stevideter.com/2008/12/07/saveorupdate-versus-merge-in-hibernate

- Saving detached entities : http://blog.xebia.com/2009/03/jpa-implementation-patterns-saving-detached-entities

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Published by David Gimelle - dans Java
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kasani 10/12/2015 10:15

its nice explanation why the exception comes and i wanna know how can we achieve from this exception(NonUniqueObjetException)...please help me

kasani 10/12/2015 10:13

how can we achieve from this exception...please help me

Binh Nguyen 14/10/2015 07:13

Thanks, nice tips

linus 07/07/2015 15:21

wha is the solution for this ?


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  • David Gimelle
  • Java Developer for more 10 years. I worked in France, Canada and Switzerland. I am contractor in London since 2010.
  • Java Developer for more 10 years. I worked in France, Canada and Switzerland. I am contractor in London since 2010.


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