SqlCacheDependency Application

代码

缓存设计：
         SqlCacheDependency类在所有受支持的 SQL Server 版本 ( 7.0 ,  2000 ,  2005 ) 上监视特定的 SQL Server 数据库表，以便在该表发生更改时，自动从 Cache 中删除与该表关联的项。SqlCacheDependency 类向应用程序的 Cache 添加依赖于 SQL Server 数据库表或 SQL 查询的项.
      建立连接对象，再创建一个SqlCommand实例，创建SqlCacheDependency实例，在这步之后再调用Command对象来获取数据（这个顺序很重要）。之后调用Cache的Insert语句建立一个依赖于一个具体查询数据集的Cache项。
Example Code：
      public  List < Bookmark >  GetBookmarkByUserId( string  userId, SqlCacheDependency dependency)
        {
            List < Bookmark >  bookmarks  =   new  List < Bookmark > ();
             string  cmdText = string .Format ( " select Id,Name,Url,FolderId,Type from dbo.Bookmark where UserId='{0}' " ,userId);

             using  (SqlConnection con  =   new  SqlConnection(“connectionString”))
            {
                con.Open();
                SqlCommand cmd  =   new  SqlCommand(cmdText);
                dependency  =   new  SqlCacheDependency(cmd); // 添加sql缓存依赖 SqlCacheDependency数据库表发生更改时，将自动删除缓存项。

                 using  (SqlDataReader dr  =  cmd.ExecuteReader(CommandBehavior.CloseConnection))
                {
                     while  (dr.Read())
                    {
                        Bookmark mark  =   new  Bookmark()
                        {
                            Id  =  dr.GetString( 0 ),
                            Name  =  dr.GetString( 1 ),
                            Url  =  dr.GetString( 2 ),
                            Type  =  dr.GetString( 4 )
                        };

                        bookmarks.Add(mark);
                    }
                }
            }

             return  bookmarks;
           
        }

         public  List < Bookmark >  GetBookamrks( string  userId,  int  timeout)
        {

            List < Bookmark >  bookmarks  =   new  List < Bookmark > ();

             string  key  =   " userId_ "   +  userId;
            bookmarks  =  (List < Bookmark > )HttpRuntime.Cache[key];

             //  Check if the data exists in the data cache
             if  (bookmarks  ==   null )
            {
                SqlCacheDependency dependency  =   null ;
                 //  If the data is not in the cache then fetch the data from the business logic tier
                bookmarks  =  GetBookmarkByUserId(userId,dependency);
                TimeSpan slidingExpiration  =  TimeSpan.FromHours(timeout);
                 //  Store the output in the data cache, and Add the necessary SqlCacheDependency object
                 // 绝对到期
                 //  HttpRuntime.Cache.Add(key, bookmarks, dependency, DateTime.Now.AddHours(timeout), Cache.NoSlidingExpiration, CacheItemPriority.High, null);
                 // 滑动过期
                CacheItemRemovedCallback  callBack  =   new  CacheItemRemovedCallback(onRemove);

                HttpRuntime.Cache.Add(key, bookmarks, dependency, Cache.NoAbsoluteExpiration, slidingExpiration, CacheItemPriority.High, callBack);
            }

             return  bookmarks;
        }
     // 移除Bookmark时，同时移除Version
  public   void  onRemove( string  key,  object  val, CacheItemRemovedReason reason)
        {
             if  (HttpRuntime.Cache[key  +   " version " ]  !=   null )
            {
                HttpRuntime.Cache.Remove(key  +   " version " );
            }
        }