asp.net中自定义验证控件的简单用法

        private void CustomValidator1_ServerValidate(object source, System.Web.UI.WebControls.ServerValidateEventArgs args)
        {
            string username=args.Value;
            OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OleDb.4.0;Data Source="+HttpContext.Current.Server.MapPath("db.mdb"));
            conn.Open();
            OleDbCommand cmd=new OleDbCommand("select Count(*) from GuestBook where Username='"+this.TextBox8.Text+"'",conn);
            int count=Convert.ToInt32(cmd.ExecuteScalar());
            if(count>0)
            {
                args.IsValid=false;
            }
            else
            {
                args.IsValid=true;
            }

            conn.Close();
        }

这里使用的是ACCESS数据库