ASP.NET学习笔记[缓存篇]

王朝asp·作者佚名 2006-11-24

1.Cache对象支持清扫（scavenging）：当系统资源不足时，它会自动从缓存中删除低优先级的或不常用的项。

2.在从缓存中获取一个项后，应当检查看该项是否为nothing。如果为nothing，就需要把该项重新赋值给缓存。

3.在添加一个项到缓存中时，可以把该项与一个文件关联。如果文件发生变化，则该项被自动从缓存中删除：Cache.Insert("itemName","itemValue!",New CacheDependency(MapPath("fileName.txt")))

4.设置缓存依赖，当数据库数据发生变化时，清除缓存中相应的项：

1.首先创建一个触发器：

CREATE TRIGGER UpdateCache

ON Products

FOR UPDATE, DELETE, INSERT

DECLARE @cmd Varchar( 200 )

SELECT @cmd = 'echo ' + Cast( getDATE() As Varchar( 50 ) ) +

' > c:\dataTableChange.txt'

EXEC master..xp_cmdshell @cmd, no_output

2.测试页面

<%@ Import Namespace="System.Data" %>

<%@ Import Namespace="System.Data.SqlClient" %>

Sub Page_Load

Dim dstProducts As DataSet

dstProducts = Cache( "productsDS" )

If dstProducts Is Nothing Then

dstProducts = GetProducts()

Cache.Insert( "Products", dstProducts, _

New CacheDependency( "c:\dataTableChange.txt" ) )

End If

dgrdProducts.DataSource = dstProducts

dgrdProducts.DataBind()

End Sub

Function GetProducts() As DataSet

Dim conNorthwind As SqlConnection

Dim strSelect As String

Dim dadProducts As SqlDataAdapter

Dim dstProducts As DataSet

conNorthwind = New SqlConnection( "Server=Localhost;UID=sa;PWD=XXXXXX;Database=Northwind" )

strSelect = "Select TOP 10 * From Products ORDER BY ProductID"

dadProducts = New SqlDataAdapter( strSelect, conNorthwind )

dstProducts = New DataSet()

dadProducts.Fill( dstProducts, "ProductsDS" )

Return dstProducts

End Function

</Script>

<html>

</head>

<body>

<asp:DataGrid

ID="dgrdProducts"

Runat="Server" />

</body>

</html>

注：该方法调用xp_cmdshell存储过程来完成该功能，则需要赋予访问者管理员权限，安全性差。慎用！