NHibernate IPreUpdateEventListener doesn't insert to second table

Question

I'm prototyping some simple audit logging functionality. I have a mid sized entity model (~50 entities) and I'd like to implement audit logging on about 5 or 6. Ultimately I'd like to get this working on Inserts & Deletes as well, but for now I'm just focusing on the updates.

The problem is, when I do session.Save (or SaveOrUpdate) to my auditLog table from within the EventListener, the original object is persisted (updated) correctly, but my AuditLog object never gets inserted.

I think it's a problem with both the Pre and Post event listeners being called to late in the NHibernate save life cycle for the session to still be used.

//in my ISessionFactory Build method

nHibernateConfiguration.EventListeners.PreUpdateEventListeners = 
    new IPreUpdateEventListener[]{new AuditLogListener()};


//in my AuditLogListener
public class AuditLogListener : IPreUpdateEventListener
{
    public bool OnPreUpdate(PreUpdateEvent @event)
    {
        string message = //code to look at @event.Entity & build message - this works            
        if (!string.IsNullOrEmpty(message))
            AuditLogHelper.Log(message, @event.Session); //Session is an IEventSource

        return false; //Don't veto the change
    }
}

//In my helper
public static void Log(string message, IEventSource session)
{
    var user = session.QueryOver<User>()
                      .Where(x => x.Name == "John")
                      .SingleOrDefault();
    //have confirmed a valid user is found

    var logItem = new AdministrationAuditLog
                  {
                     LogDate = DateTime.Now,
                     Message = message,
                     User = user
                  };

    (session as ISession).SaveOrUpdate(logItem);
}

When it hits the session.SaveOrUpdate() in the last method, no errors occur. No exceptions are thrown. it seems to succeed and moves on. But nothing happens. The audit log entry never appears in the database.

The only way I've been able to get this to work it to create a completely new Session & Transaction inside this method, but this isn't really ideal, as the code proceeds back out of the listener method, hits the session.Transaction.Commit() in my main app, and if that transaction fails, then I've got an orphaned log message in my audit table for somethign that never happened.

Any pointers where I might be going wrong ?

EDIT

I've also tried to SaveOrUpdate the LogItem using a child session from the events based on some comments in this thread. http://ayende.com/blog/3987/nhibernate-ipreupdateeventlistener-ipreinserteventlistener

var childSession = session.GetSession(EntityMode.Poco);
var logItem = new AdministrationAuditLog
                {
                    LogDate = DateTime.Now,
                    Message = message,
                    User = databaseLogin.User
                };

childSession.SaveOrUpdate(logItem);

Still nothing appears in my Log table in the db. No errors or exceptions.

Answer 1

You need to create a child session, currentSession.GetSession(EntityMode.Poco), in your OnPreUpdate method and use this in your log method. Depending on your flushmode setting, you might need to flush the child session as well.

Also, any particular reason you want to roll out your own solution? FYI, NHibernate Envers is now a pretty mature library.