Question

What is difference between session.Close() and session.Dispose()?

Answer 1

From the Nhibernate Source code:

private void Dispose(bool isDisposing)
{
    using (new SessionIdLoggingContext(base.SessionId))
    {
        if (!base.IsAlreadyDisposed)
        {
            log.Debug(string.Format("[session-id={0}] executing real Dispose({1})", base.SessionId, isDisposing));
            if (!(!isDisposing || base.IsClosed))
            {
                this.Close();
            }
            base.IsAlreadyDisposed = true;
            GC.SuppressFinalize(this);
        }
    }
}

So Dispose method calls Close(). Calling either Close() or Dispose() methods will close the Session not allowing you to work with it anymore.