Linq(Update)

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

    NorthwindDBDataContext dc = new NorthwindDBDataContext();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
            return;

        string id = Request.QueryString["id"].ToString();

        Users user = dc.Users.Where(x => x.Id.ToString() == id).First();

        TextBox1.Text = user.Username;
        TextBox2.Text = user.Password;
        CheckBox1.Checked = user.Sex.GetValueOrDefault();
        

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string id = Request.QueryString["id"].ToString();

        Users user = dc.Users.Where(x => x.Id.ToString() == id).First();

        user.Sex = CheckBox1.Checked;
        user.Username = TextBox1.Text;
        user.Password = TextBox2.Text;

        dc.SubmitChanges();

        Response.Redirect("default3.aspx");


    }
}