// From http://www.developmentalmadness.com/2008/07/28/linq-to-sql-reusing-datacontext/

/**************************************************************************************
 *  IThreadLocalStorageProvider.cs
 **************************************************************************************/

namespace MyApp.Web.Models
{
    public interface IThreadLocalStorageProvider
    {
        void SaveItem(string key, object value);
        object GetItem(string key);
        bool ContainsItem(string key);
    }

    public class ThreadLocalStorageProviderFactory
    {
        public static IThreadLocalStorageProvider Current { get; set; }
    }
}

/**************************************************************************************
 *  WebThreadLocalStorageProvider.cs
 **************************************************************************************/

namespace MyApp.Web.Models
{
    using System.Web;

    public class WebThreadLocalStorageProvider : IThreadLocalStorageProvider
    {
        public void SaveItem(string key, object value)
        {
            HttpContext.Current.Items.Add(key, value);
        }

        public object GetItem(string key)
        {
            return HttpContext.Current.Items[key];
        }

        public bool ContainsItem(string key)
        {
            return HttpContext.Current.Items.Contains(key);
        }
    }
}

/**************************************************************************************
 *  MyAppDataContext.cs (partial class)
 **************************************************************************************/

namespace MyApp.Web.Models 
{
    using System;
    using System.Collections.Generic;
    using System.Data.Linq;

    public partial class MyAppDataContext
    {
        public static MyAppDataContext GetDataContext()
        {
            // if TLS isn't available just return a new DataContext
            if (ThreadLocalStorageProviderFactory.Current == null)
                return new MyAppDataContext();

            MyAppDataContext context;

            // check to see if DataContext already exists in TLS
            if (ThreadLocalStorageProviderFactory.Current.ContainsItem("DataContext"))
            {
                // get DataContext
                context = ThreadLocalStorageProviderFactory.Current.GetItem("DataContext") as MyAppDataContext;

                // verify DataContext
                if (context != null) return context;
            }

            // if we got here, then just create a new DataContext
            context = new MyAppDataContext();

            // cache the DataContext
            ThreadLocalStorageProviderFactory.Current.SaveItem("DataContext", context);

            // return to caller
            return context;
        }
    }
}

/**************************************************************************************
 *  Global.asax.cs
 **************************************************************************************/

namespace MyApp.Web
{
    using System;
    using System.Data;
    using System.Data.Linq;
    using System.Security.Principal;
    using System.Web;
    using System.Web.Mvc;
    using System.Web.Optimization;
    using System.Web.Routing;
    using System.Web.Security;
    using MyApp.Web.Models;

    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_EndRequest(object sender, EventArgs e)
        {
            // Validate that we actually have a DataContext to evaluate.
            if (!ThreadLocalStorageProviderFactory.Current.ContainsItem("DataContext")) return;

            // Create an instance of the DataContext
            var ctx = ThreadLocalStorageProviderFactory.Current.GetItem("DataContext") as DataContext;

            // If the instanciated DataContext is not null and connected, destroy it.
            if (ctx != null && ctx.Connection.State == ConnectionState.Open) ctx.Dispose();
        }
    }
}