Question

I see the need to copy and paste the following error handling code several times. What are my options when working within a Catch statement?

• In doing so, will I lose valuable information in the process? (example: are exceptions re-wrapped in another exception, or loss of stack information)

• How can someone tell the difference between a “throw” in myAbstractClass and one in the Select method below?

Here is sample code I want to replicate

public class StackUserDataSource : AbstractEnhancedTableDataSource<StackUserDataServiceContext>
{
  //.. stuff

 public IEnumerable<StackUserDataModel> Select() 
    {
        try
        {
            var results = from c in _ServiceContext.StackUserTable
                          select c;

            var query = results.AsTableServiceQuery();
            var queryResults = query.Execute();

            return queryResults;
        }
        catch (StorageClientException e)
        {

           // Todo: consider sticking this in another central location    
            switch (e.ErrorCode)
            {
                case StorageErrorCode.AccessDenied:
                    break;
                case StorageErrorCode.AccountNotFound:
                    break;
                case StorageErrorCode.AuthenticationFailure:
                    break;
                // ... Yadda yadda, handle some exceptions, not others.. this is a demo.
                case StorageErrorCode.TransportError:
                    break;
                default:
                    break;
            }
            throw;
        }
    }

Update:

I doubt this is possible, but can I dynamically catch and filter exceptions in an external library? The concept goes like this

        try
        {
            var results = from c in _ServiceContext.StackUserTable
                          select c;

            var query = results.AsTableServiceQuery();
            var queryResults = query.Execute();

            return queryResults;
        }
        catch (MyExternalExceptionHelperDLL e)
        {
            // all exceptions referenced in MyExternalHelper are passed below
            MyExternalExceptionHelper.ProcessException(e);
         }
         catch (exception)
        {
         }

Since it’s probably not possible for the MyExternalExceptionHelperDLL to dynamically pick and choose what to listen for (i.e. SQL, vs Networking vs File, but not authentication)

        try
        {
            var results = from c in _ServiceContext.StackUserTable
                          select c;

            var query = results.AsTableServiceQuery();
            var queryResults = query.Execute();

            return queryResults;
        }
         catch (exception e)
        {
           MyExternalExceptionHelper.ProcessException(e);

           // The problem is that I don't know how to catch exceptions thrown from that static method above,
           // or how to override that exception handling...
        }

But with the above code, its not clear to me how the end user can opt into or override my methods of event handling.

Answer 1

You could do something like this. The important part is that the throw needs to be in the original catch block in order to preserve the stack trace.

public IEnumerable<StackUserDataModel> Select() 
{
    try
    {
        ...
    }
    catch (StorageClientException e)
    {
       // You could do this if there is no fancy processing to do
       if (!IsCatchableException(e))
          throw;
    }
}

bool IsCatchableException(StorageClientException e)
{
    ... optionally do some fancy processing of the exception, e.g. logging....
    switch (e.ErrorCode)
    {
        case StorageErrorCode.AccessDenied:
        case StorageErrorCode.AccountNotFound:
        ....
        return true;
    }
}