Load connection string from ConfigurationManager : ConfigurationManager « Configuration « ASP.NET Tutorial

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="FromConfig" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Connection String from Config</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Button ID="Button1" runat="server" Text="Go get data..." OnClick="Button1_Click" />
        <hr />
        <asp:DropDownList runat="server" ID="CustomerList" />
    </div>
    </form>
</body>
</html>

File: Default.aspx.cs

using System;
using System.Data;
using System.Configuration;
using System.Data.SqlClient;
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;

public partial class FromConfig : System.Web.UI.Page
{

    protected void Button1_Click(object sender, EventArgs e)
    {
        string connString = ConfigurationManager.ConnectionStrings["LocalNWind"].ConnectionString;

        using (SqlConnection conn = new SqlConnection(connString))
        {
            string cmdText = "SELECT * FROM customers";
            SqlCommand cmd = new SqlCommand(cmdText, conn);
            cmd.Connection.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            CustomerList.Items.Clear();
            while (reader.Read())
                CustomerList.Items.Add(reader["companyname"].ToString());
            reader.Close();
             cmd.Connection.Close();
        }
    }
}

File: Web.config

<?xml version="1.0"?>
<configuration>
...
  <connectionStrings>
    <add name="LocalNWind" connectionString="SERVER=(local);DATABASE=northwind;Trusted_Connection=yes;" />
  </connectionStrings>
...
</configuration>
16.11.ConfigurationManager
	16.11.1.	Load connection string from ConfigurationManager