Why does NHibernate throw "StaleObjectStateException"?

Question

I am writing project and using NHibernate 3.1

SimpleTest:

Forum forum = Session.CreateCriteria<Forum>().Add(Restrictions.Eq("UrlName", "reportabug")).UniqueResult<Forum>();
forum.TopicsCount++;
IForumRepository forumRepository = new ForumRepository(SessionFactory);
forumRepository.Update(forum);

public virtual void Update(TEntity entity)
{
    if (!session.Transaction.IsActive)
    {
        TResult result;
        using (var tx = session.BeginTransaction())
        {
            session.SaveOrUpdate(entity)
            tx.Commit();
        }
        return result;
    }
    session.SaveOrUpdate(entity)
}

The last update throws exception:

StaleObjectStateException was unhandled by user code:
    Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect)

SQL query:

UPDATE Forums
SET    Name = 'Forums Issues (not product support)' /* @p0 */,
       UrlName = 'reportabug' /* @p1 */,
       Description = 'Use this forum to report issues with the online forums application. When reporting an issue please include relevant details such as repro steps, error messages and browser version.' /* @p2 */,
       CategoryId = 'b2cc232c-0d5c-4f35-bb6f-29c67d7d40c2' /* @p3 */,
       TopicsCount = 1 /* @p4 */
WHERE  ForumId = '864046b7-ca57-48c4-8a81-082103223527' /* @p5 */

ForumId is correct. Maybe this is concurrency? Have any ideas?

Answer 1

StaleObjectStateException is a way of hibernate ensuring data consistency read the API here. Hibernate maintains the version of objects it updates and will throw an error if the version in DB and in memory does not match. Read more about the optimistic locking mechanism here.

So, Debug the application with this information. I am not familiar with C# syntax but I think the second save should be in else condition.