Launch a custom Exception

Question

I have a method in my Webservice that throws an exception if the card code is already in use, that is, when trying to free the access the system checks if it is already in use and returns to Exception.

Code in the Webservice

... 
try
{
    if(ListaCartoes.Any(c => c.Codigo == cartaoParaAcesso)
       throw new Exception("CARTÃO JÁ ESTÁ EM USO");
}
catch(Exception ex)
{
  throw new ErroLiberacaoDeAcesso(ex.message);
}

Code on the Client

...
try
  {
      Webservice.LiberaAcesso(informacoesAcesso);        
  }
  catch(Exception ex)
  {
       MessageBox.Show(ex.message);
  }

Code Class Erroraccess:

 [Serializable()]
    public class ErroLiberaAcesso: Exception
    {
        public ErroLiberaAcesso() : base()
        { }

        public ErroLiberaAcesso(string message) : base(message)
        { }

        public ErroLiberaAcesso(string message, Exception innerException) : base(message, innerException)
        { }

        protected ErroLiberaAcesso(SerializationInfo info, StreamingContext context) : base(info, context)
        { }
    }

Error that is returning:

Exception = {"System.Web.Services.Protocols.Soapexception: The server could not process the request. ---> Pca_webservice_v2.Errorsaccess: CARD NUMBER IN USE n

That is, it is not only the "CARD NUMBER IN USE" message that is returning. What can I do in this case ?

Answer 1

From what I understand you have a business rule and not an exceptional situation. Then you should not use this mechanism. The last thing you should do in this case is to replace a if simple-for-a catch complex.

Before using a language resource, understand what it’s for.

Especially the way you’re doing where you generate a general exception, then the catch, which makes no sense at all in doing this (it’s the worst exception abuse I’ve ever seen) and then releasing another one that has a misnamed (it should be LiberaAcessoException). But the name isn’t even the problem, it’s its existence and its use. If it is business rule, treat in the normal flow of the system, generating a return that informs the situation.

Then the webservice would look something like this:

 //faz o que tem que fazer aqui (se é que tem algo mais)
 return ListaCartoes.Any(c => c.Codigo == cartaoParaAcesso)

On the client:

if (Webservice.LiberaAcesso(informacoesAcesso)) {
    //faz algo aqui se tiver que fazer
} else {
    MessageBox.Show("CARTÃO JÁ ESTÁ EM USO");
}

I put in the Github for future reference.

If you have other reasons for mistakes in the business rule, it can change the logic a little. In this case it would probably create a class to encapsulate the error information and send it as a return, rather than a boolean.

That class would be too similar to an exception, but would not be a, avoiding the long detours (goto in its worst form) and unpredictability of the action, not to mention the slowness and the possibility of misuse of the mechanism, as occurs (note that the current code is saying that the card is already in use even if you have a programming error or other system failure, as the System.Web.Services.Protocols.SoapException).

If class is something exaggerated for you, return another form of code/message as I do demonstrate in another question.

Doing the right thing might uncover other issues in your code that you didn’t even know about because you were using the feature the wrong way.