using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.Caching;

using System.Data;

public partial class CACHE查询条件 : System.Web.UI.Page

{

    protected void Button1_Click(object sender, EventArgs e)

    {

        string cond = "";

        if (this.DropDownList1.SelectedIndex > 0)

        {

             cond += "stu_sex='" + this.DropDownList1.SelectedValue + "'";

        }

        else

        {

             cond += "1=1";

        }

        if (this.TextBox1.Text != "")

        {

            cond += " and age=" + this.TextBox1.Text;

        }

        ViewState["cond"] = cond;

        Page_Load(null, null);

    }

    //页面加载时，将DataSet插入到委托中去。

    protected void Page_Load(object sender, EventArgs e)

    {

        //首先从Cache中获取Dataset

        DataSet students = (DataSet)Cache["Students"];

        //如果Cache中不存在DataSet，则从数据库中获取DataSet，并添加到缓存中

        if (students == null)

        {

            students = GetStudentDataSet();

            //创建一个基于web.config配置文件的依赖，当该文件发生变化时，则从缓存中移除缓存项。

            CacheDependency cd = new CacheDependency(Server.MapPath("web.config"));

            //在Insert中指定该依赖项，并且指定缓存的优先级为高优先级，传递一个传托。

            Cache.Insert("Students", students, cd, System.Web.Caching.Cache.NoAbsoluteExpiration, TimeSpan.FromHours(1));

        }

        DataView view = students.Tables[0].DefaultView;

        if (ViewState["cond"] != null)

        {

            view.RowFilter = ViewState["cond"].ToString();

        }

        GridView1.DataSource = view;

        //GridView1.DataSource = students;

        GridView1.DataBind();

    }

    /// <summary>

    /// 从数据库中获取产品信息，并返回一个DataSet对象

    /// </summary>

    /// <returns></returns>

    protected DataSet GetStudentDataSet()

    {

        string sql = "select * from t_student";

        DataSet ds = DBHelper.SqlHelper.ExecuteDataSetText(sql, null);

        return ds;

    }

}