There is now an ELMAH.MVC package in NuGet that includes an improved solution by Atif and also a controller that handles the elmah interface within MVC routing (no need to use that axd anymore)
The problem with that solution (and with all the ones here) is that one way or another the elmah error handler is actually handling the error, ignoring what you might want to set up as a customError tag or through ErrorHandler or your own error handler
The best solution IMHO is to create a filter that will act at the end of all the other filters and log the events that have been handled already. The elmah module should take care of loging the other errors that are unhandled by the application. This will also allow you to use the health monitor and all the other modules that can be added to asp.net to look at error events
I wrote this looking with reflector at the ErrorHandler inside elmah.mvc
public class ElmahMVCErrorFilter : IExceptionFilter
{
private static ErrorFilterConfiguration _config;
public void OnException(ExceptionContext context)
{
if (context.ExceptionHandled) //The unhandled ones will be picked by the elmah module
{
var e = context.Exception;
var context2 = context.HttpContext.ApplicationInstance.Context;
//TODO: Add additional variables to context.HttpContext.Request.ServerVariables for both handled and unhandled exceptions
if ((context2 == null) || (!_RaiseErrorSignal(e, context2) && !_IsFiltered(e, context2)))
{
_LogException(e, context2);
}
}
}
private static bool _IsFiltered(System.Exception e, System.Web.HttpContext context)
{
if (_config == null)
{
_config = (context.GetSection("elmah/errorFilter") as ErrorFilterConfiguration) ?? new ErrorFilterConfiguration();
}
var context2 = new ErrorFilterModule.AssertionHelperContext((System.Exception)e, context);
return _config.Assertion.Test(context2);
}
private static void _LogException(System.Exception e, System.Web.HttpContext context)
{
ErrorLog.GetDefault((System.Web.HttpContext)context).Log(new Elmah.Error((System.Exception)e, (System.Web.HttpContext)context));
}
private static bool _RaiseErrorSignal(System.Exception e, System.Web.HttpContext context)
{
var signal = ErrorSignal.FromContext((System.Web.HttpContext)context);
if (signal == null)
{
return false;
}
signal.Raise((System.Exception)e, (System.Web.HttpContext)context);
return true;
}
}
Now, in your filter config you want to do something like this:
public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
//These filters should go at the end of the pipeline, add all error handlers before
filters.Add(new ElmahMVCErrorFilter());
}
Notice that I left a comment there to remind people that if they want to add a global filter that will actually handle the exception it should go BEFORE this last filter, otherwise you run into the case where the unhandled exception will be ignored by the ElmahMVCErrorFilter because it hasn't been handled and it should be loged by the Elmah module but then the next filter marks the exception as handled and the module ignores it, resulting on the exception never making it into elmah.
Now, make sure the appsettings for elmah in your webconfig look something like this:
<add key="elmah.mvc.disableHandler" value="false" /> <!-- This handles elmah controller pages, if disabled elmah pages will not work -->
<add key="elmah.mvc.disableHandleErrorFilter" value="true" /> <!-- This uses the default filter for elmah, set to disabled to use our own -->
<add key="elmah.mvc.requiresAuthentication" value="false" /> <!-- Manages authentication for elmah pages -->
<add key="elmah.mvc.allowedRoles" value="*" /> <!-- Manages authentication for elmah pages -->
<add key="elmah.mvc.route" value="errortracking" /> <!-- Base route for elmah pages -->
The important one here is "elmah.mvc.disableHandleErrorFilter", if this is false it will use the handler inside elmah.mvc that will actually handle the exception by using the default HandleErrorHandler that will ignore your customError settings
This setup allows you to set your own ErrorHandler tags in classes and views, while still loging those errors through the ElmahMVCErrorFilter, adding a customError configuration to your web.config through the elmah module, even writing your own Error Handlers. The only thing you need to do is remember to not add any filters that will actually handle the error before the elmah filter we've written. And I forgot to mention: no duplicates in elmah.
