Asp. NET Database Cache Dependency Instance Analysis _ Practical Tips

This article describes the ASP.net database cache dependency, share to everyone for reference. Specifically as follows:

Generally in asp.net, the cool feature of the cache class is that it can control its behavior according to various dependencies. file-based dependencies are most useful, and file dependencies are added by CacheDependency objects that use Cache.Insert and provide reference files.

Copy Code code as follows:

Cache.Insert ("MyData", Source, New CacheDependency (Server.MapPath ("Authors.xml"));

But what to do when we want the cache to fail and rebuild the cache based on the changes in the tables in the database--a scenario that exists in many applications. ASP.net does not provide intrinsic direct caching support for monitoring database table changes. This is done by using the infrequently used system stored procedures of SQL Server, a stored procedure used to generate Web pages from a query, but we just have to make a little change-using it in triggers, and we can get a reasonable and effective way to sp_makewebtask. Modifying a particular file when a record of a table in a database is updated, deleted, or modified will cause the file monitoring process in the CacheDependency instance to detect changes in the file, thereby invalidating the cache. In fact, because the CacheDependency class works on UNC file protocols, we can deploy this solution across the Web farm, Web The copy of the application on each machine on the farm will monitor the same file on a single machine in webfarm via a UNC file path

With less nonsense, let's create a simple Web application to demonstrate if it works. First, we'll use the Northwind sample database that we all trust in SQL Server. Create a simple DataGrid to display the records in the Employees table. The first thing we need to do is create triggers.

Copy Code code as follows:

CREATE TRIGGER writecachedepfile on [dbo]. [Employees]
For INSERT, UPDATE, DELETE
As
EXEC sp_makewebtask ' \\peter\C$\Cache\mycache.txt ', ' SELECT top 1 FirstName from Employees '

The above stored procedure is simply to tell SQL Server, if any changes in the employee table, based on a simple query to update the "mycache.txt" file, there is a simple query statement is actually enough, as long as it is a valid T-SQL statement The server will be happy to update the file.

Next, we need to create a directory and set it to be shared. You may want to update the file's access rights so that it can be written, notice that I am using the admin share "C $" here. In addition, you need to create an empty text file, "Mycache.txt".

OK, now it's time to create our application. First, enter the dependent file name in the Web.config file so that we do not need to redeploy the application when we modify the dependent file.

At the root of the Web.config file, add the appsettings configuration section:

Copy Code code as follows:

</system.web>
<appSettings>
<!-Cache-dependent file path-->
<add key= "Dependencyfile" value= "\\peter\Cache\mycache.txt"/>
</appSettings>
</configuration>

Now let's create a caching mechanism in the global class so that we don't need to write specific code on any page

Copy Code code as follows:

public class Global:System.Web.HttpApplication
{
Cache _cache =null;
public static bool Blnreflash = FALSE;
Public Const string CONNSTR = "server=localhost;database=northwind;uid=sa;pwd=";
Public Const string strSQL = "Select EmployeeID, LastName, FirstName from Employees";
protected void Application_Start (Object sender, EventArgs e)
{
_cache = Context.cache;
Refreshcahe (null,null,0);
}
protected void Session_Start (Object sender, EventArgs e)
{
if (httpcontext.current.cache[) Employee S "]==null)
RefreshCache (null,null,0);
}
static void RefreshCache (string key,object item,cacheitemremovereason reason)
{
SqlDataAdapter ad Apter = new SqlDataAdapter (STRSQL,CONNSTR); The
DataSet ds = new DataSet ();
Adapter. Fill (ds, "Employees");
CacheItemRemovedCallback onremove = new CacheItemRemovedCallback (RefreshCache);
}

I hope this article will help you with the ASP.net program design.