Question

In my Service classes I create an exception instance like this:

protected ServiceException _ex;

protected void Initialize()
{
    _ex = new ServiceException();
}

Later in these classes I call this exception if something goes wrong:

    public void Delete<T, V>(T item, V repo)
        where T : Microsoft.WindowsAzure.StorageClient.TableServiceEntity
        where V : IAzureTable<T>
    {
        try
        {
            repo.Delete(item);
        }
        catch (Exception ex)
        {
            _ex.Errors.Add("", "Error when deleting " + typeof(T).Name.ToLower());
            throw _ex;
        }
    }

Outside of this in the controller I check for the exception:

    catch (Exception e) { log(e); }

Then I handle this:

    protected void log(Exception ex)
    {
        if (ex is ServiceException)
        {
            ModelState.Merge(((ServiceException)ex).Errors);  
        }
        else
        {
            Trace.Write(ex);
            ModelState.AddModelError("", "Database access error: " + ex.Message);
        }
    }

Sorry for the long example but what I would like to know is if this is a valid thing for me to be doing. In particular someone commented that I am creating a new value of _ex every time even if there’s no exception. Well my reason for doing this was that each controller has about twenty try-catch blocks and I thought it better to just create an _ex object at the start and so not have to have twenty areas where I create a new _ex if something goes wrong. I’d appreciate if someone could tell me if this all makes sense. Thanks.

Answer 1

I would suggest collecting errors in a separate structure and then just passing it in the exception class constructor whilst throw so you do not create an instance of exception class unless really need it:

// class constructor, List of strings or any entity like ErrorEntry
IList<string> errors = new List<string>();

// collect while execution
errors.Add(errorText);    

// raise an exception
throw new ServiceException(this.errors);

BTW, can you give some examples when you track an error but do not raising an exception?