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Simple NHibernate Architecture

, 11 Sep 2012
An article showing a nice architecture I've come up for using NHibernate
nhibernatesample.zip
NHibernateSample
Business
bin
Debug
Business.dll
Business.pdb
Castle.DynamicProxy.dll
Iesi.Collections.dll
log4net.dll
NHibernate.dll
Shared.NHibernateDAL.dll
Shared.NHibernateDAL.pdb
NHibernateDAL.cd
obj
Debug
Business.dll
Business.pdb
ResolveAssemblyReference.cache
TempPE
Properties
NHibernateDAL
bin
Debug
Castle.DynamicProxy.dll
Iesi.Collections.dll
log4net.dll
NHibernate.dll
NHibernateDAL.dll
NHibernateDAL.pdb
Shared.NHibernateDAL.dll
Shared.NHibernateDAL.pdb
mssccprj.scc
NHibernateDAL.csproj.vspscc
obj
Debug
NHibernateDAL.dll
NHibernateDAL.pdb
Refactor
NHibernateDAL.dll
Shared.NHibernateDAL.dll
ResolveAssemblyReference.cache
Shared.NHibernateDAL.dll
Shared.NHibernateDAL.pdb
TempPE
Properties
vssver2.scc
Shared.NHibernateDAL.csproj.vspscc
vssver2.scc
Web
App_Data
Bin
Business.dll
Business.pdb
Castle.DynamicProxy.dll
Iesi.Collections.dll
log4net.dll
NHibernate.dll
Shared.NHibernateDAL.dll
Shared.NHibernateDAL.pdb
using System;
using System.Collections.Generic;
using System.Runtime.Remoting.Messaging;
using System.Text;
using NHibernate;
using NHibernate.Cache;
using System.Web;
using System.Data;
using System.Configuration;

namespace Shared.NHibernateDAL
{
	/// <summary>
	/// Handles creation and management of sessions and transactions.  It is a singleton because 
	/// building the initial session factory is very expensive. Inspiration for this class came 
	/// from Chapter 8 of Hibernate in Action by Bauer and King.  Although it is a sealed singleton
	/// you can use TypeMock (http://www.typemock.com) for more flexible testing.
	/// </summary>
	public sealed class NHibernateSessionManager
	{
		#region Thread-safe, lazy Singleton

		/// <summary>
		/// This is a thread-safe, lazy singleton.  See http://www.yoda.arachsys.com/csharp/singleton.html
		/// for more details about its implementation.
		/// </summary>
		public static NHibernateSessionManager Instance
		{
			get
			{
				return Nested.nHibernateSessionManager;
			}
		}

		/// <summary>
		/// Initializes the NHibernate session factory upon instantiation.
		/// </summary>
		private NHibernateSessionManager()
		{
			InitSessionFactory();
		}

		/// <summary>
		/// Assists with ensuring thread-safe, lazy singleton
		/// </summary>
		private class Nested
		{
			static Nested() { }
			internal static readonly NHibernateSessionManager nHibernateSessionManager = new NHibernateSessionManager();
		}

		#endregion

		private void InitSessionFactory()
		{
			NHibernate.Cfg.Configuration cfg = new NHibernate.Cfg.Configuration();

			// The following makes sure the the web.config contains a declaration for the HBM_ASSEMBLY appSetting
			if (ConfigurationManager.AppSettings["HBM_ASSEMBLY"] == null ||
				ConfigurationManager.AppSettings["HBM_ASSEMBLY"] == "")
			{
				throw new ConfigurationErrorsException("NHibernateManager.InitSessionFactory: \"HBM_ASSEMBLY\" must be " +
					"provided as an appSetting within your config file. \"HBM_ASSEMBLY\" informs NHibernate which assembly " +
					"contains the HBM files. It is assumed that the HBM files are embedded resources. An example config " +
					"declaration is <add key=\"HBM_ASSEMBLY\" value=\"MyProject.Core\" />");
			}

			cfg.AddAssembly(System.Configuration.ConfigurationManager.AppSettings["HBM_ASSEMBLY"]);
			sessionFactory = cfg.BuildSessionFactory();
		}

		/// <summary>
		/// Allows you to register an interceptor on a new session.  This may not be called if there is already
		/// an open session attached to the HttpContext.  If you have an interceptor to be used, modify
		/// the HttpModule to call this before calling BeginTransaction().
		/// </summary>
		public void RegisterInterceptor(IInterceptor interceptor)
		{
			ISession session = threadSession;

			if (session != null && session.IsOpen)
			{
				throw new CacheException("You cannot register an interceptor once a session has already been opened");
			}

			GetSession(interceptor);
		}

		public ISession GetSession()
		{
			return GetSession(null);
		}

		/// <summary>
		/// Gets a session with or without an interceptor.  This method is not called directly; instead,
		/// it gets invoked from other public methods.
		/// </summary>
		private ISession GetSession(IInterceptor interceptor)
		{
			ISession session = threadSession;

			if (session == null)
			{
				if (interceptor != null)
				{
					session = sessionFactory.OpenSession(interceptor);
				}
				else
				{
					session = sessionFactory.OpenSession();
				}

				threadSession = session;
			}

			return session;
		}

		public void CloseSession()
		{
			ISession session = threadSession;
			threadSession = null;

			if (session != null && session.IsOpen)
			{
				session.Close();
			}
		}

		public void BeginTransaction()
		{
			ITransaction transaction = threadTransaction;

			if (transaction == null)
			{
				transaction = GetSession().BeginTransaction();
				threadTransaction = transaction;
			}
		}

		public void CommitTransaction()
		{
			ITransaction transaction = threadTransaction;

			try
			{
				if (transaction != null && !transaction.WasCommitted && !transaction.WasRolledBack)
				{
					transaction.Commit();
					threadTransaction = null;
				}
			}
			catch (HibernateException ex)
			{
				RollbackTransaction();
				throw ex;
			}
		}

		public void RollbackTransaction()
		{
			ITransaction transaction = threadTransaction;

			try
			{
				threadTransaction = null;

				if (transaction != null && !transaction.WasCommitted && !transaction.WasRolledBack)
				{
					transaction.Rollback();
				}
			}
			catch (HibernateException ex)
			{
				throw ex;
			}
			finally
			{
				CloseSession();
			}
		}

		internal ITransaction threadTransaction
		{
			get
			{
				return (ITransaction)CallContext.GetData("THREAD_TRANSACTION");
			}
			set
			{
				CallContext.SetData("THREAD_TRANSACTION", value);
			}
		}

		private ISession threadSession
		{
			get
			{
				return (ISession)CallContext.GetData("THREAD_SESSION");
			}
			set
			{
				CallContext.SetData("THREAD_SESSION", value);
			}
		}

		private ISessionFactory sessionFactory;
	}
}

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About the Author

Cassio Mosqueira
Software Developer (Senior) Intelligent Coder
Canada Canada
I've been developing .NET enterprise applications since 2000.
 
I am originally from Rio de Janeiro and I am currently working at http://www.intelligentcoder.com in Ontario.

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