Question

I currently have some code that delibratly throws an exception if the user sends me data that fails validation (see below). I like it because im sure any errors in the application are caught and handled. A am however worried the code being slow as throwing exceptions takes a lot of memory. Im also worried it might be “bad code”. Whats your advice? Thanks

  public class BTAmendAppointmentRequest
    {
        public DataLayer.WebserviceMessage AddBTAmendAppointmentRequest(DataLayer.BTAmendAppointmentRequest req)
        {
            DataLayer.WebserviceMessage rsp = new DataLayer.WebserviceMessage();
            try
            {

                if (!String.IsNullOrEmpty(req.AppointmentReference))
                    req.AppointmentReference = req.AppointmentReference.Trim();

                if (req.OrderRequestID < 1 || string.IsNullOrEmpty(req.AppointmentReference))
                {
                    throw new Exception("Amend appointment failed, you must supply a valid appointment reference and order reference");
                }

        ...Do other stuff
            }
            catch (Exception ex)
            {
                rsp = new Service.WebserviceErrorMessage(ex);
            }


            return rsp;

        }

    }

Answer 1

If you are expecting these errors, you should return error messages to the user, not throw exceptions.

Reserve exceptions to exceptional situations.

Apart from being expensive, the meaning of an exception, the semantics are that of something exceptional having happened. Validation failing is not exceptional, it is expected.

Having said that, seeing as you are on a web service, an exception is a reasonable thing to do, assuming you also validate before the service call. It is reasonable since a web service can be called by anything – validation may not have happened, and such errors should be exceptional. Additionally, at least with .NET web services, web exceptions are probably the best way to communicate such things back to the client.