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

         //定義索引名稱
         const string ContextKey = "TYEntities";

         //標記為ThreadStaticAttribute的靜態字段不在線程之間共享。
         //每個執行線程都有單獨的字段實例，并且獨立地設置及獲取該字段的值。如果在不同的線程中訪問該字段，則該字段將包含不同的值。
         [ThreadStatic]
         private static TYEntities _current;

         #endregion

         #region Properties

         public bool Disposed { get; set; }

         /// <summary>
         /// 當系統工作在HttpContext下，將使用延遲家在技術返回一個TYEntities（ObjectContext），如果沒有HttpContext將返回null
         ///
         /// 不論在哪里使用TYEntities，在請求結束后都需要調用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;

                 //檢查HttpContext是否存在
                 if (context != null)
                 {
                     //試著從context中得到TYEntities
                     var result = context.Items[ContextKey] as TYEntities;

                     if (result == null)
                     {
                         //創建新的datacontext，并且保存到context里面
                         result = new TYEntities();
                         context.Items[ContextKey] = result;
                     }

                     return result;
                 }

                 return null;
             }
         }

         /// <summary>
         /// 這是一個用來獲取TYEntities(ObjectContext)的公共屬性
         ///
         /// 如果你通過HttpContext獲取TYEntities，同樣不論在哪里使用TYEntities，在請求結束后都需要調用TYEntities.Cleanup()方法
         ///
         /// 如果沒有通過HttpContext獲取TYEntities，你必須在使用結束之后調用TYEntities.Cleanup()方法，來清理ObjectContext。
         ///
         /// 需要注意的一點是，無論使用哪種方式獲取TYEntities，我們都必須手動的清理和Dispose TYEntities(ObjectContext)。
         /// 所以一定不要在using塊中使用TYEntities(ObjectContext)。
         /// </summary>
         public static TYEntities Current
         {
             get
             {
                 //從HttpContext中獲取datacontext
                 var result = TYEntities.ForWebRequest;

                 if (result != null)
                     return result;

                 //試著獲取當前活動的TYEntities
                 if (_current == null)
                     _current = new TYEntities();

                 return _current;
             }
         }

         /// <summary>
         /// 清理結束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
     }
 }