Simple NHibernate Architecture

using System;
using System.Collections.Generic;
using System.Text;
using NHibernate;
using System.Runtime.Remoting.Messaging;

namespace Shared.NHibernateDAL
{
	public class TransactionBlock : IDisposable	
	{
		public TransactionBlock()
		{
			object obj = new object();

			if (ActiveTransactions == 0)
			{
				NHibernateSessionManager.Instance.BeginTransaction();				
			}
			ActiveTransactions++;
		}


		private int ActiveTransactions
		{
			get
			{
				return CallContext.GetData("Active_Transactions") == null ? 0 : Convert.ToInt32(CallContext.GetData("Active_Transactions"));
			}
			set
			{
				CallContext.SetData("Active_Transactions", value);
			}
		}

		private void DisposeActiveTransacions()
		{
			CallContext.SetData("Active_Transactions", null);
		}

		private bool _isValid = false;
		public bool IsValid
		{
			set { _isValid = value; }
		}

		public void Dispose()
		{
			ActiveTransactions--;
			if (_isValid)
			{
				if (_isValid && ActiveTransactions == 0 && NHibernateSessionManager.Instance.GetSession().Transaction.IsActive)
				{
					DisposeActiveTransacions();
					NHibernateSessionManager.Instance.CommitTransaction();
				}
			}
			else if (NHibernateSessionManager.Instance.GetSession().Transaction.IsActive)
			{
				DisposeActiveTransacions();
				NHibernateSessionManager.Instance.RollbackTransaction();
			}
		}

	}
}