วิธี Connect Database SQL Server 2005 ของ C# ผ่าน App.Config และวิธีเรียกใช้หน่อยครับ

<appSettings>
		<add key="ConS" value="Server =Servername;uid=sa;password=1234;database=DBname;"/>
</appSettings>

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.IO;
using System.Data.SqlClient;
using System.Configuration;
public static class Copncon
{
	static SqlCommand sCommd = new SqlCommand();
	static AppSettingsReader abc = new AppSettingsReader();

	static SqlConnection ConSQL = new SqlConnection(abc.GetValue("ConS", "".GetType()).ToString());

	public static SqlCommand Copencon()
	{
		sCommd.Connection = ConSQL;
		ConSQL.Open();
		return sCommd;
	}
}

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
	<appSettings>
		<!-- Connection string -->
		<add key="SqlConnectionString" value="server=localhost;uid=sa;password=;database=mydatabase;Max Pool size=400;Connect Timeout=600;Connection Lifetime=600;pooling=false" />
		
	</appSettings>
</configuration>

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.IO;
using System.Data.SqlClient;

namespace MyApp
{

    class DB
    {
        private SqlConnection objConn;
        private SqlCommand objCmd;
        private String strConnString;

        public DB()
        {
            strConnString = System.Configuration.ConfigurationSettings.AppSettings["SqlConnectionString"];
        }


        public DataSet dsDataSet(String strSQL)
        {
            DataSet ds = new DataSet();
            SqlDataAdapter dtAdapter = new SqlDataAdapter();
            objConn = new SqlConnection();
            objConn.ConnectionString = strConnString;
            objConn.Open();

            objCmd = new SqlCommand();
            objCmd.Connection = objConn;
            objCmd.CommandText = strSQL;
            objCmd.CommandType = CommandType.Text;

            dtAdapter.SelectCommand = objCmd;
            dtAdapter.Fill(ds);
            return ds;   //*** Return DataSet ***//
        }

        public DataTable dtDataTable(String strSQL)
        {
            SqlDataAdapter dtAdapter;
            DataTable dt = new DataTable();
            objConn = new SqlConnection();
            objConn.ConnectionString = strConnString;
            objConn.Open();

            dtAdapter = new SqlDataAdapter(strSQL, objConn);
            dtAdapter.Fill(dt);
            return dt; //*** Return DataTable ***//
        }

        public Boolean exExecuteNonQuery(String strSQL)
        {
            objConn = new SqlConnection();
            objConn.ConnectionString = strConnString;
            objConn.Open();

            try
            {
                objCmd = new SqlCommand();
                objCmd.Connection = objConn;
                objCmd.CommandType = CommandType.Text;
                objCmd.CommandText = strSQL;

                objCmd.ExecuteNonQuery();
                return true; //*** Return True ***//
            }
            catch (Exception)
            {
                return false; //*** Return False ***//
            }
        }
}

public DB()
{

strConnString = System.Configuration.ConfigurationSettings.AppSettings["SqlConnectionString"];
}