WCF Error Type Identification

Question

I have a WCF service which I am using with a WPF application.

I am trying to achieve error handling so that the service will provide instructions to the user depending on the error i.e. (e.g. code error writes to log and informs user to contact support) vs (e.g. trying to write duplicate value into a unique field informs user of field with duplicate and asks to change value and try again ... no log entry)

I have successfully created my error DataContract and I can get the data in my WPF application. In fact the whole system works as desired. My problem however is the following section of code is playing havoc with my OCD. It seems hack and slash.

try
{
    db.SaveChanges();
}
catch (Exception ex)
{
    String message = "";

    if (ex.InnerException.ToString()
          .Contains("Cannot insert duplicate key row") == false)
    {
        logError le = new logError();
        le.log(ex, "AddTemplate");

        message = "An error has occured, 
                   please contact you support representative";
    }
    else
    {
        message = "Code already exists";
    }

    throw new FaultException<myError>
              (new myError { Operation = "Add Template",
                             ProblemType = message });
}

Is there a better way of identifying the error in order to send a specific message to the client other than what I have done here. The String.Contains part is the part that really bothers me.

Byron Lo · Answer 1 · 2013-10-24T07:37:44.013

1

In general, I believe it is best practice to always switch on error codes instead of performing string comparisons on error messages.

catch (SqlException ex)
{
    if (ex.Errors.Count > 0)
    {
        switch (ex.Errors[0].Number)
        {
            case 547: //foreign Key violation
                //throw or handle FK violation
                break;
            case 2601: //primary key violation
                //throw or handle PK violation
                break;
            default:
                //throw or handle 'Other' violation
                break;
        }
    }

    //throw or handle "general" errors.
}

List of error codes http://msdn.microsoft.com/en-us/library/cc645728.aspx

It may also be best practice to have your own services return errors codes too so that other applications you build that want to reuse these services in the future but want to display different types of error messages (e.g. graphical error icons or alternative text) will not be forced to perform a .Contains() on the string you're returning :-)

edited Oct 24 '13 at 07:37

answered Oct 24 '13 at 07:32

Byron Lo

474
2
7

When I add (SqlException ex) when it hits db.SaveChanges(); with an invalid index value it just goes straight to WPF general error, it doesn't even go through the case statement. – Animus Miles-Militis Oct 24 '13 at 08:18
I found a solution to using SQL Errors http://stackoverflow.com/questions/8645233/entity-framework-4-2-getting-proper-database-errors?lq=1 – Animus Miles-Militis Oct 24 '13 at 09:08
Ah, my code was just a general example to show error code usage, it wasn't meant to be used directly in your code. Sorry for the misunderstanding – Byron Lo Oct 24 '13 at 09:42

WCF Error Type Identification

1 Answers1