NHibernate Session Per Web Request

LazySessionContext.cs

using System;
using System.Collections.Generic;
using System.Web;
using NHibernate;
using NHibernate.Context;
using NHibernate.Engine;

namespace WebHub.Infrastracture.SessionManagement
{
    public class LazySessionContext : ICurrentSessionContext
    {
        private readonly ISessionFactoryImplementor factory;
        private const string CurrentSessionContextKey = "NHibernateCurrentSession";

        public LazySessionContext(ISessionFactoryImplementor factory)
        {
            this.factory = factory;
        }

        /// <summary>
        /// Retrieve the current session for the session factory.
        /// </summary>
        /// <returns></returns>
        public ISession CurrentSession()
        {
            Lazy<ISession> initializer;
            var currentSessionFactoryMap = GetCurrentFactoryMap();
            if(currentSessionFactoryMap == null || 
                !currentSessionFactoryMap.TryGetValue(factory, out initializer))
            {
                return null;
            }
            return initializer.Value;
        }

        /// <summary>
        /// Bind a new sessionInitializer to the context of the sessionFactory.
        /// </summary>
        /// <param name="sessionInitializer"></param>
        /// <param name="sessionFactory"></param>
        public static void Bind(Lazy<ISession> sessionInitializer, ISessionFactory sessionFactory)
        {
            var map = GetCurrentFactoryMap();
            map[sessionFactory] = sessionInitializer;
        }

        /// <summary>
        /// Unbind the current session of the session factory.
        /// </summary>
        /// <param name="sessionFactory"></param>
        /// <returns></returns>
        public static ISession UnBind(ISessionFactory sessionFactory)
        {
            var map = GetCurrentFactoryMap();
            var sessionInitializer = map[sessionFactory];
            map[sessionFactory] = null;
            if(sessionInitializer == null || !sessionInitializer.IsValueCreated) return null;
            return sessionInitializer.Value;
        }

        /// <summary>
        /// Provides the CurrentMap of SessionFactories.
        /// If there is no map create/store and return a new one.
        /// </summary>
        /// <returns></returns>
        private static IDictionary<ISessionFactory, Lazy<ISession>> GetCurrentFactoryMap()
        {
            var currentFactoryMap = (IDictionary<ISessionFactory,Lazy<ISession>>)
                                    HttpContext.Current.Items[CurrentSessionContextKey];
            if(currentFactoryMap == null)
            {
                currentFactoryMap = new Dictionary<ISessionFactory, Lazy<ISession>>();
                HttpContext.Current.Items[CurrentSessionContextKey] = currentFactoryMap;
            }
            return currentFactoryMap;
        }
    }
    
    public interface ISessionFactoryProvider
    {
        IEnumerable<ISessionFactory> GetSessionFactories();
    }

    public class SessionFactoryProvider
    {
        public const string Key = "NHibernateSessionFactoryProvider";
    }

    public class NHibernateSessionModule : IHttpModule
    {
        private HttpApplication app;
        private ISessionFactoryProvider sfp;

        public void Init(HttpApplication context)
        {
            app = context;
            sfp = (ISessionFactoryProvider) context.Application[SessionFactoryProvider.Key];
            context.BeginRequest += ContextBeginRequest;
            context.EndRequest += ContextEndRequest;
        }

        private void ContextBeginRequest(object sender, EventArgs e)
        {
            foreach (var sf in sfp.GetSessionFactories())
            {
                var localFactory = sf;
                LazySessionContext.Bind(
                    new Lazy<ISession>(() => BeginSession(localFactory)), 
                    sf);
            }
        }

        private static ISession BeginSession(ISessionFactory sf)
        {
            var session = sf.OpenSession();
            session.BeginTransaction();
            return session;
        }

        private void ContextEndRequest(object sender, EventArgs e)
        {
            foreach (var sf in sfp.GetSessionFactories())
            {
                var session = LazySessionContext.UnBind(sf);
                if (session == null) continue;
                EndSession(session);
            }
        }

        private static void EndSession(ISession session)
        {
            if(session.Transaction != null && session.Transaction.IsActive)
            {
                session.Transaction.Commit();
            }
            session.Dispose();
        }

        public void Dispose()
        {
            app.BeginRequest -= ContextBeginRequest;
            app.EndRequest -= ContextEndRequest;
        }
    }
}

//Example of IWindsorInstaller:
public class NHibernateInstaller : IWindsorInstaller
{
    #region IWindsorInstaller Members

    public void Install(IWindsorContainer container, IConfigurationStore store)
    {
        container.Register(Component.For<ISessionFactory>()
                               .UsingFactoryMethod(k => BuildSessionFactory()));

        container.Register(Component.For<NHibernateSessionModule>());

        container.Register(Component.For<ISessionFactoryProvider>().AsFactory());
        
        container.Register(Component.For<IEnumerable<ISessionFactory>>()
                                    .UsingFactoryMethod(k => k.ResolveAll<ISessionFactory>()));

        HttpContext.Current.Application[SessionFactoryProvider.Key]
                        = container.Resolve<ISessionFactoryProvider>();
    }

    #endregion
    public ISessionFactory BuildSessionFactory() { ... }
}

//Example of dao
public class Dao<T> : IDao<T>
{
    private readonly ISessionFactory sessionFactory;

    public Dao(ISessionFactory sessionFactory)
    {
        this.sessionFactory = sessionFactory;
    }

    public void Save(T transient)
    {
        sessionFactory.GetCurrentSession().Save(transient);
    }

http://nhforge.org/blogs/nhibernate/archive/2011/03/03/effective-nhibernate-session-management-for-web-apps.aspx