如何使用NHibernate实现ChangeTime和ChangeUser列？

public class MyEntity
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual DateTime ChangeTime { get; set; }
    public virtual string ChangeUser { get; set; }
}

 <class name="MyEntity" table="MyEntity">
    <id name="Id" column="Id">
     <generator class="identity" />
    </id>
   <property name="Name" column="Name" />
   <property name="ChangeTime" column="ChangeTime" />
   <property name="ChangeUser" column="ChangeUser" />
  </class>
</hibernate-mapping>

public class AuditEventListener : IPreUpdateEventListener, IPreInsertEventListener
{
    public bool OnPreUpdate(PreUpdateEvent @event)
    {
        SetChangeTimeAndUser(@event.Persister, @event.State, @event.Session);
        return false;
    }

    public bool OnPreInsert(PreInsertEvent @event)
    {
        SetChangeTimeAndUser(@event.Persister, @event.State, @event.Session);
        return false;
    }

    private void SetChangeTimeAndUser(IEntityPersister persister, object[] state, ISession session)
    {
        int changeTimeIndex = Array.IndexOf(persister.PropertyNames, "ChangeTime");
        int changeUserIndex = Array.IndexOf(persister.PropertyNames, "ChangeUser");

        if (changeTimeIndex >= 0)
        {
            state[changeTimeIndex] = DateTime.UtcNow;
        }

        if (changeUserIndex >= 0)
        {
            state[changeUserIndex] = session.SessionFactory.CurrentSessionContext.Session.GetSessionImplementation().Connection.ConnectionString;
        }
    }
}

var configuration = new Configuration();
configuration.Configure();
configuration.EventListeners.PreInsertEventListeners = new IPreInsertEventListener[] { new AuditEventListener() };
configuration.EventListeners.PreUpdateEventListeners = new IPreUpdateEventListener[] { new AuditEventListener() };