public bool IsvalidUser(string ID, string Password)
            {
                Connectionstring = Class_String.con;
                if (ID.Length == 0)
                {
                    errormessage.Text = "Enter an ID or Password.";
                    TextBoxID.Focus();
                }
                else if (ID.Length <= 4 || Password.Length <= 4)
                {
                    errormessage.Text = "Invalid ID Or Password.";
                    TextBoxID.Focus();
                }
                else
                {
                    try
                    {
                        using (var db = new Models.ModelContext())
                        {
                            var query = from p in db.LoginModel
                                        where p.Student_Enrolletman == ID
                                        && p.Student_Password == Password
                                        select p;
                           
                            if (query.Any())
                            {
                                return true;
                            }
                            else
                            {
                                return false;
                            }
                            db.SaveChanges();
                        }