0 Comments

Available on NuGet

Including ELFAR (MVC) and ELFAR (Web API) in your web application is extremely easy.  However, if you're anything like me then you'll hate the idea of having to create two instances of the error log provider (assuming that you've referenced the same providers).  You can manually combine the files but, to save you the bother, I've done the leg work for you:

0 Comments

Introduction

There has been a steady uptake of Error Logging Filter and Route (ELFAR) for ASP.NET MVC since I introduced it, back in February.  Just a few days before that post, Microsoft released ASP.NET MVC 4 Beta (now RC), which includes ASP.NET Web API.  Although part of ASP.NET MVC 4, ASP.NET Web API uses completely different namespaces (and can be hosted independently), which means that ELFAR couldn't be plugged in automatically, so I decided to see if it was possible to adapt ELFAR for ASP.NET Web API.

Adapting ELFAR

As the two technologies follow the same architecture, it was a simple process to create the Web API ErrorLogFilter and ErrorLogRoute.  They are almost identical to the MVC ErrorLogFilter and ErrorLogRoute, apart from the base classes that they derive from (and the Web API ErrorLogRoute doesn't need to override the GetRouteData or GetVirtualPath methods).  However, to maintain the separation of concerns between ASP.NET MVC and ASP.NET Web API, the common interfaces and classes needed to be moved out of the MVC class library and into their own class library (Elfar.Core).  With that, Error Logging Filter and Route (ELFAR) for ASP.NET Web API was created.

Like ELFAR (MVC), add ELFAR (Web API) to your website/web application with just 4 lines of code (usually in the Application_Start method):

var config = GlobalConfiguration.Configuration;
var provider = new ErrorLogProvider();
config.Filters.Add(new ErrorLogFilter(provider));
config.Routes.Add("elfar", new ErrorLogRoute(provider));
Figure 1

The same but different

Whilst the filters behave identically, the routes provide very different functionality.  Where the MVC version provides the web GUI, for viewing the error logs, the Web API version acts as an ErrorLogProvider by returning either the list of error logs or a single error log.

Available on NuGet

ELFAR (Web API) uses the same error log providers as ELFAR (MVC):

0 Comments

Erik Funkenbusch posted a question, on the ELFAR discussion board, regarding the logging of handled exceptions. He managed to figure out a solution and kindly posted it:

FYI, I found a solution that works pretty well.

try
{
    throw new NotImplementedException();
}
catch (Exception e)
{
    foreach (var filter in GlobalFilters.Filters)
    {
        if (filter.Instance is ErrorLogFilter)
        {
            var f = filter.Instance as ErrorLogFilter;
            f.OnException(new ExceptionContext(ControllerContext, e));
        }
    }
}

I actually took this one step further and created a .Log() extension method on Exception.

public static class ExceptionExtensions
{
    public static void Log(this Exception exception, ControllerContext context)
    {
        foreach (var filter in GlobalFilters.Filters)
        {
            if (filter.Instance is ErrorLogFilter)
            {
                var f = filter.Instance as ErrorLogFilter;
                f.OnException(new ExceptionContext(context, exception));
            }
        }
    }
}

Then you just need to use it as such:

try
{
    throw new NotImplementedException();
}
catch (Exception e)
{
    //...
    e.Log(ControllerContext);
}

However, there is an alternative solution: throw the exception and let ELFAR automatically handle it (Figure 1).

try
{
    throw new NotImplementedException();
}
catch (Exception)
{
    //...
    throw;
}
Figure 1

Update:

Erik responded with some good points:

Rethrowing the exception will result in an unhandle exception propogating to the client...The whole point is to handle th[e] exception, but log it so it can be investigated. I find this particularly useful with exceptions for external resources (Web requests, file access, etc..). There is no point in passing this on to the user if you can continue.

0 Comments

Introduction

Error Logging Filter and Route (ELFAR) for ASP.NET MVC was inspired by and based on the popular Error Logging Modules And Handlers (ELMAH) for ASP.NET utility. ELFAR retains the familiar ELMAH user interface but has been built to utilise the architecture of ASP.NET MVC. Unlike ELMAH, ELFAR is not driven by configuration and can be added to your website/web application with just 3 lines of code (usually in the Application_Start method):

var provider = new ErrorLogProvider();
GlobalFilters.Filters.Add(new ErrorLogFilter(provider));
RouteTable.Routes.Insert(0, new ErrorLogRoute(provider));
Figure 1

To access ELFAR, navigate to ~/elfar (where ~/ is the root directory of the MVC application).

Available on NuGet

ELFAR has 6 out-of-the-box error log providers:

Features

Once ELFAR has been added to your website/web application, you get the following features:

  • a web page to view a list of error logs
  • a web page to view the details of an error log, including a coloured stack trace
  • a view of the original yellow screen of death (where appropriate)
  • XML and JSON downloads of the error log
  • an RSS feed of the last 15 error logs
  • an RSS digest of daily error logs (limited to 900)
  • a CSV download of all error logs
    •    

Optional features

In addition, there are several optional features available:

  • Excluding unwanted exceptions
  • Restricting access to the ELFAR web pages
  • Email notification of errors   
  • Posting errors to Twitter
    •    

Resources

Further information can be found in the ELFAR Wiki.
Full source for ELFAR can be found at SourceForge.net (Subversion) or GitHub