asp.net链接Access数据库字符串正确方法

在web  config中  作如下配置：
<connectionStrings>
    <add name="ydycon" connectionString="Provider=Microsoft.Jet.OLEDB.4.0;
Data Source=|DataDirectory|ydy.mdb" providerName="System.Data.OleDb"/>
 
  </connectionStrings>
在.net文件中应用链接字符串：
 
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.OleDb;
using System.Data.SqlClient;  //添加引用
using System.Text;
using System.IO;
using System.Collections;
public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
     // string ConStr = "Server=(./SQLEXPRESS);DataBase=|Datadrictory|db_17.mdf;Uid=;Pwd=";
            string cmdtxt = "SELECT * from tb_13";
            OleDbConnection Con = new OleDbConnection(System.Configuration .ConfigurationManager.ConnectionStrings ["ydycon"].ToString() );
            //OleDbConnection Con = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + Server.MapPath("ydy.mdb"));
           // SqlConnection Con = new SqlConnection(ConStr);
            Con.Open();
            OleDbDataAdapter da = new OleDbDataAdapter(cmdtxt, Con);
           // SqlDataAdapter da = new SqlDataAdapter(cmdtxt, Co