实现自动抛弃当前数据库上下文的模块。支持各种ORM框架并存

一：OrmContextAutoDisposeModule.cs

EventHandler PostRequestHandlerExecute

MSDN：在 ASP.NET 事件处理程序（例如，某页或某个 XML Web service）执行完毕时发生。

也就是说注册这个事件的方法可以做一些页面执行完毕的清理工作。如果页面中引入了某个DBContext或者是DataContext，一般情况下这些数据库资源是需要释放的，好处很多就不多少了。注册这个事件，可以在页面执行完毕时统一进行一些清理的工作。因此程序员在编程的时候也没有必要做一些using的资源释放的活了。

 
 
namespace  MyCompanyName.WebHelpers

{ 

///<summary>/// 实现自动抛弃当前数据库上下文的模块。
///</summary>publicsealedclass OrmContextAutoDisposeModule : IHttpModule
{
    #region IHttpModule 成员
    public void Init(HttpApplication context)
    {
        context.PostRequestHandlerExecute += new EventHandler(Enter);
    }

    public void Dispose()
    {
    }
    #endregion

    private void Enter(object sender, EventArgs e)
    {

// DataContext或DBContext是以键值对的形式存在了Items中，Items是HttpContext很重要的数据存储单位 

        IDictionary httpContextItems = HttpContext.Current.Items;

// 获取DBContext 或 DataContext 或 ObjectContext
        List<object> keys = new List<object>(httpContextItems.Count);
        foreach (DictionaryEntry item in httpContextItems)
        {
            if (item.Value is DataContext || item.Value is ObjectContext || item.Value is DbContext)
            {
                ((IDisposable)item.Value).Dispose();
                keys.Add(item.Key);
            }
        }

        foreach (object key in keys)
        {
            httpContextItems.Remove(key);
        }
    }
}

} 

二.在Web.config文件中注册Module

        <httpModules>
            <add name="OrmContextAutoDisposeModule" type="MyCompanyName.WebHelpers.OrmContextAutoDisposeModule, MyCompanyName.WebHelpers"/>
        </httpModules> 

三：OrmContextFactory.cs 

public static class OrmContextFactory
{
    public static TDataContext GetDataContext<TDataContext>()
        where TDataContext : DataContext, new()
    {
        HttpContext httpContext = HttpContext.Current;
        if (httpContext != null)
        {
            string key = typeof(TDataContext).FullName;

            TDataContext dataContext = httpContext.Items[key] as TDataContext;
            if (dataContext == null)
            {
                dataContext = new TDataContext();
                httpContext.Items[key] = dataContext;
            }
            return dataContext;
        }

        return new TDataContext();
    }

    public static TObjectContext GetObjectContext<TObjectContext>()
        where TObjectContext : ObjectContext, new()
    {
        HttpContext httpContext = HttpContext.Current;
        if (httpContext != null)
        {
            string key = typeof(TObjectContext).FullName;

            TObjectContext objectContext = httpContext.Items[key] as TObjectContext;
            if (objectContext == null)
            {
                objectContext = new TObjectContext();
                httpContext.Items[key] = objectContext;
            }
            return objectContext;
        }

        return new TObjectContext();
    }

    public static TDbContext GetDbContext<TDbContext>()
        where TDbContext : DbContext, new()
    {
        HttpContext httpContext = HttpContext.Current;
        if (httpContext != null)
        {
            string key = typeof(TDbContext).FullName;

            TDbContext dbContext = httpContext.Items[key] as TDbContext;
            if (dbContext == null)
            {
                dbContext = new TDbContext();
                httpContext.Items[key] = dbContext;
            }
            return dbContext;
        }

        return new TDbContext();
    }
}