An NHibernate audit trail that doesn't cause “collection was not processed by flush” errors

Question

Ayende has an article about how to implement a simple audit trail for NHibernate (here) using event handlers.

Unfortunately, as can be seen in the comments, his impl

Answer 1

The fix should be the following. Create a new event listener class and derive it from NHibernate.Event.Default.DefaultFlushEventListener:

[Serializable] 
public class FixedDefaultFlushEventListener: DefaultFlushEventListener 
{
    private static readonly log4net.ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);

    protected override void PerformExecutions(IEventSource session)
    {
        if (log.IsDebugEnabled)
        {
            log.Debug("executing flush");
        }
        try
        {
            session.ConnectionManager.FlushBeginning();
            session.PersistenceContext.Flushing = true;
            session.ActionQueue.PrepareActions();
            session.ActionQueue.ExecuteActions();
        }
        catch (HibernateException exception)
        {
            if (log.IsErrorEnabled)
            {
                log.Error("Could not synchronize database state with session", exception);
            }
            throw;
        }
        finally
        {
            session.PersistenceContext.Flushing = false;
            session.ConnectionManager.FlushEnding();
        }

    }
} 

Register it during NHibernate configuraiton:

cfg.EventListeners.FlushEventListeners = new IFlushEventListener[] { new FixedDefaultFlushEventListener() };

You can read more about this bug in Hibernate JIRA: https://hibernate.onjira.com/browse/HHH-2763

The next release of NHibernate should include that fix either.