public TL_USER_ByIdResult TL_USER_ById(string userID)
 {
     try
     {
         using (var db = new OOAD_EDUManagementDataContext())
         {
             return db.TL_USER_ById(userID).FirstOrDefault();
         }
     }
     catch (Exception e)
     {
         return null;
     }
 }