c# 數據庫連接問題！

Question

我想用APP.CONFIG 文件連接數據庫！ 配置文件 如下：
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
  </configSections>
  <connectionStrings>    <add name="MyConnectionString"
        connectionString= "server =172.16.3.133 ;database=Northwind;user id=sa;password=123456"
         providerName="System.Data.SqlClient" />  </connectionStrings>
</configuration>然後我 新增了個控制台程序
準備查找  NORTHWIND 數據庫的內容！
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
using System.Configuration; 
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {            string connString = System.Configuration.ConfigurationSettings.AppSettings["MyConnectionString"].ToString();//這一條就出錯了
            SqlConnection conn = new SqlConnection(connString);
            conn.Open();
            SqlCommand thiscommand = conn.CreateCommand();
            thiscommand.CommandText = "select customerid,companyname from customers";
            SqlDataReader thisreader = thiscommand.ExecuteReader();
            while (thisreader.Read())
            {
                Console.WriteLine("\t{0}\t{1}",
                    thisreader["customerid"], thisreader["companyname"]);
            }
            conn.Close();
            Console.Write("以下空白");
            Console.ReadLine();        }
    }
}
請幫忙分析下，或者教我 如何用類連接數據庫！

Answer 1

string connString = System.Configuration.ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;

Answer 2

Add Reference :find 'System.Configuration' and add it;
 use it:ConfigurationManager.AppSettings[""].ToString();

Answer 3

System.Configuration.ConfigurationManager.AppSettings["MyConnectionString"].Trim();

Answer 4

這個必須要添加 .NET 引用
有沒更好的方法 

Answer 5

System.Configuration.ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
就可以了呀

Answer 6

string connString = System.Configuration.ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;