Good day,

I am using Hibernate from within Tomcat as a service, and outside of Tomcat in a loose standing application. These two clients are accessing the database concurrently, so this causes duplicate ID's to be generated by Hibernate.

Any ideas on a solution to the problem will be greatly appreciated.

Kind regards,
Sitrac

This should be impossible, if you are using the built-in id generation strategies correctly.

Does Hibernate check the latest ID in the database before assigning a new one, or does it keep these entries in cache? In other words, if I were to add a database record manually without restarting a Hibernate session, will the Hibernate id generator create the correct id for a new entry?

Post your code and mapping files.

Below is the mapping for the class, a hibernate utility class and a shortened piece of source showing how the class is saved.

PostgreSQL responds with the following error:

org.postgresql.util.PSQLException: ERROR: duplicate key violates unique constraint "note_pkey"

After restarting Tomcat, the system works fine.

******************* NOTE MAPPING ***********************

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
<class
name="com.vhr.util.Note"
table="note"
dynamic-update="false"
dynamic-insert="false"
>

<id
name="id"
column="note_id"
type="java.lang.Long"
>
<generator class="increment">
</generator>
</id>

<property
name="text"
type="java.lang.String"
update="true"
insert="true"
access="property"
column="text"
/>

<property
name="timestamp"
type="java.util.Date"
update="true"
insert="true"
access="property"
column="timestamp"
/>

<!--
To add non XDoclet property mappings, create a file named
hibernate-properties-Note.xml
containing the additional properties and place it in your merge dir.
-->

</class>

</hibernate-mapping>

******************* HIBERNATE UTILITY CLASS *****************

package com.vhr.hibernate;

import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.Session;
import net.sf.hibernate.HibernateException;
import net.sf.hibernate.cfg.Configuration;
import net.*;
/**
* To-do: import javax.servlet.Servlet;
*/
public class HibernateUtil {

/**
* Todo: implements Servlet{
*/
private static final SessionFactory sessionFactory;
public static final ThreadLocal session = new ThreadLocal();

static {
try {
// Create the SessionFactory
sessionFactory = new Configuration().configure().buildSessionFactory();
} catch (HibernateException ex) {
throw new RuntimeException("Configuration problem: " + ex.getMessage(), ex);
}
}

/**
* @return net.sf.hibernate.Session
* @throws net.sf.hibernate.HibernateException
*/
public static Session currentSession() throws HibernateException {
Session s = (Session) session.get();
// Open a new Session, if this Thread has none yet
if (s == null) {
s = sessionFactory.openSession();
session.set(s);
}
return s;
}

/**
* @throws net.sf.hibernate.HibernateException
*/
public static void closeSession() throws HibernateException {
Session s = (Session) session.get();
session.set(null);
if (s != null)
s.close();
}
}

******************* SAVING A NOTE ************************

net.sf.hibernate.Session sess = com.vhr.hibernate.HibernateUtil.currentSession();
net.sf.hibernate.Transaction tran = sess.beginTransaction();

com.vhr.Vehicle vehicleUpdate = (com.vhr.Vehicle) sess.load(com.vhr.Vehicle.class, new Long(request.getParameter("update")));

vehicleUpdate.getTheTrackingDevice().getStatusHistory().addNote(new com.vhr.util.Note("Test Status: "+request.getParameter("lmTestStatus")));

sess.save(vehicleUpdate);
tran.commit();
com.vhr.hibernate.HibernateUtil.closeSession();

Maybe try saveOrUpdate instead of save?

http://www.hibernate.org/hib_docs/refer ... g-detached

It is not possible to use the increment generator when multiple applications access the same table. It only fetches a maximum at startup and does an internal increment from then on. Look at
http://www.hibernate.org/hib_docs/reference/en/html/mapping.html#mapping-declaration-id-generator
and choose a different strategy.

Bart

Thank you Bart