No defining declaration found for implementing declaration of partial method

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LINQ

Hello


I am new to linq and I am using ‘LINQ To Sql’ Tutorial Series , I used the code like below for updating the phone number of

customers table (sample 1) and then add a class and named it "customer.cs" (sample 2)

for preventing bogus phone numbers from being added into our database.

Now when I debug the program I take the error like below (sample 3) ,

please help what is the problem actually I don't know how I have to define partial class

just I know this class should works with "customer" in northwind.desiner.cs.

Thanks in advanced.


Sample 1:

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

namespace WebApplication1
{
    public partial class _Default : System.Web.UI.Page
    {
        

        protected void Page_Load(object sender, EventArgs e)
        {
           NorthwindDataContext northwind=new NorthwindDataContext();
           Customer mycustumer = northwind.Customers.Single(c => c.CompanyName == "B's Beverages");
           mycustumer.Phone = "999";
           northwind.SubmitChanges();
           



        }
    }
}

sample 2:

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Text.RegularExpressions;


namespace WebApplication1
{
    public partial class customer
    {
        partial void onphonechanging(string value)
        {
            Regex phoneNumber = new Regex(@"^[2-9]\d{2}-\d{3}-\d{4}$");

            if (phoneNumber.IsMatch(value) == false)
            {
                throw new Exception("not valid");
            }

            
        }
    }
}