using System;  using System.Collections.Generic;  using System.Linq;  using System.Text;  using System.Threading.Tasks;  using System.Web;  namespace TYStudioDemo.Models  {      public partial class TYEntities      {          #region Fields          //定义索引名称          const string ContextKey = "TYEntities";          //标记为ThreadStaticAttribute的静态字段不在线程之间共享。          //每个执行线程都有单独的字段实例，并且独立地设置及获取该字段的值。如果在不同的线程中访问该字段，则该字段将包含不同的值。          [ThreadStatic]          private static TYEntities _current;          #endregion          #region Properties          public bool Disposed { get; set; }          /// <summary>          /// 当系统工作在HttpContext下，将使用延迟家在技术返回一个TYEntities（ObjectContext），如果没有HttpContext将返回null          ///          /// 不论在哪里使用TYEntities，在请求结束后都需要调用TYEntities.Cleanup()方法          /// 最佳的方式是TYEntities.Cleanup()放到Global.asax.cs文件里面。          /// void Application_EndRequest(object sender, EventArgs e)          /// {          ///     TYStudioDemo.Models.TYEntities.Cleanup();          /// }          /// </summary>          private static TYEntities ForWebRequest          {              get              {                  var context = HttpContext.Current;                  //检查HttpContext是否存在                  if (context != null)                  {                      //试着从context中得到TYEntities                      var result = context.Items[ContextKey] as TYEntities;                      if (result == null)                      {                          //创建新的datacontext，并且保存到context里面                          result = new TYEntities();                          context.Items[ContextKey] = result;                      }                      return result;                  }                  return null;              }          }          /// <summary>          /// 这是一个用来获取TYEntities(ObjectContext)的公共属性          ///          /// 如果你通过HttpContext获取TYEntities，同样不论在哪里使用TYEntities，在请求结束后都需要调用TYEntities.Cleanup()方法          ///          /// 如果没有通过HttpContext获取TYEntities，你必须在使用结束之后调用TYEntities.Cleanup()方法，来清理ObjectContext。          ///          /// 需要注意的一点是，无论使用哪种方式获取TYEntities，我们都必须手动的清理和Dispose TYEntities(ObjectContext)。          /// 所以一定不要在using块中使用TYEntities(ObjectContext)。          /// </summary>          public static TYEntities Current          {              get              {                  //从HttpContext中获取datacontext                  var result = TYEntities.ForWebRequest;                  if (result != null)                      return result;                  //试着获取当前活动的TYEntities                  if (_current == null)                      _current = new TYEntities();                  return _current;              }          }          /// <summary>          /// 清理结束TYEntities(ObjectContext)          /// </summary>          public static void Cleanup()          {              if (HttpContext.Current != null)              {                  var result = HttpContext.Current.Items[ContextKey] as TYEntities;                  if (result != null)                      result.Dispose();                  HttpContext.Current.Items[ContextKey] = null;              }              else if (_current != null)              {                  _current.Dispose();                  _current = null;              }          }            protected override void Dispose(bool disposing)          {              bool disposed = Disposed;              Disposed = true;              if (!disposed)                  Cleanup();              base.Dispose(disposing);          }          #endregion      }  }