【转】系统缓存全解析二：动态缓存（3）－文件，对象缓存依赖与数据库缓存依赖

（依据文件，数据库，表等变化而自动更新缓存内容）

一，缓存文件：

      
简单语言介绍以下，将硬盘中的文本文件缓存至web服务器内存中，一般常用在缓存配置文件或其他公共文件上，并自动监听文件是否有被修改，一旦被修改，将自动的更新缓存。因为与下面的数据库缓存依赖基本代码一致，所以不加代码示例。

二，缓存非序列化对象或者序列化对象：

不用多说，就是将对象放入缓存内啦。

三，数据库缓存依赖项：

为了实现.NET缓存依赖需要调用System.Web.Caching下的三个类：

1，Cache类 ；//将数据缓存到该对象内；

2，SqlCacheDependency类；//主要负责为Cache对象 与 数据库表或结果集合建立关系的类

3，SqlCacheDependencyAdmin类；//可忽略不用，以后总结

以及System.Data.SqlClient下的两个类：

1，System.Data.SqlClient.SqlDependency   //开启或关闭对于数据库的监听

以及开启MSSQL内某一数据库的消息传递服务：

           alter database Common set enable_broker  
//开启

           alter database Common set disable_broker //关闭

下面是详细的。NET针对MSSQL缓存依赖项的例程：

using System;
using System.Collections.Generic;
using
System.Linq;
using System.Text;
using System.Web.Caching;
using
System.Collections;
using System.Data.SqlClient;
using
System.Data;
using System.Xml;
using
System.Collections.ObjectModel;
using System.Web;

namespace HOSoft.Herp4.AutoTest.Common.Data
{
    public sealed
class CacheProvider<T>
    {
        #region 全局变量
        public
static Cache HerpCache = HttpRuntime.Cache;
        public static
CacheItemRemovedCallback Callback = new
CacheItemRemovedCallback(CacheProvider<T>.RemovedItemCallBack);
       
public static TimeSpan timespan;
        #endregion
       
       
//#region 静态构造函数
        //static CacheProvider()
        //{
       
//    HerpCache = new Cache();
        //}
       
//#endregion

        public static void StartSqlDependency(Collection<string>
StrConnection)
        {
           
            if
(StrConnection.Count > 0)
            {
                foreach (string
str in StrConnection)
                {
                   
SqlDependency.Start(str);
                }
            }
        }

        public static void StopSqlDependency(Collection<string>
StrConnection)
        {
            if (StrConnection.Count >
0)
            {
                foreach (string str in
StrConnection)
                {
                   
SqlDependency.Stop(str);
                }
               
           
}
        }

        public static SqlCacheDependency
CreateSqlCacheDependency(SqlCommand Sqlcommand)
        {
            if
(Sqlcommand.GetHashCode() != 0)
            {
               
SqlCacheDependency SCacheDependency = new
SqlCacheDependency(Sqlcommand);
                return
SCacheDependency;
            }
            else
           
{
                return null;
            }
        }

        public static bool AddItemInCache(string DataName, T DataValue,
SqlCommand Command,String DataBase_Name)
        {
            if
(!string.IsNullOrEmpty(DataName) && DataValue.GetHashCode() !=
0)
            {
                if (HerpCache[DataName] ==
null)
                {
                    switch
(DataBase_Name.Trim().ToLower())
                   
{
                        case "common": timespan = new TimeSpan(24, 0,
0);
                            break;

                        case "house":timespan = new TimeSpan(24, 0,
0);
                            break;

                        case "oa":timespan = new TimeSpan(12, 0,
0);
                            break;

                        case "report":timespan = new TimeSpan(24, 0,
0);
                            break;
                        default:
timespan = new TimeSpan(6, 0, 0);
                            break;

                    }
                    HerpCache.Add(DataName,
DataValue, CreateSqlCacheDependency(Command), Cache.NoAbsoluteExpiration,
timespan, CacheItemPriority.High, Callback);

                    return true;
                }
               
else
                return false;
            }
           
else
            return false;
        }

        public static bool RemoveItemFromCache(string DataName)
       
{
            if (string.IsNullOrEmpty(DataName))
           
{
                if (HerpCache[DataName] != null)
               
{
                    HerpCache.Remove(DataName);
                   
return true;

                }
                else return false;
           
}
            return false;
        }

        public static void RemovedItemCallBack(string key,Object
value,CacheItemRemovedReason reason)
        {
        }

    }
}

引用地址：http://hi.baidu.com/jiangyangw3r/item/4290ff0235a2d112cd34ea6c