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What is ELMAH and how to Work ELMAH in Asp.Net MVC?

Royce Roy213907-Oct-2014

I am trying to use ELMAH to log errors in my ASP.NET MVC application, however, when I use the [HandleError] attribute on my controllers ELMAH doesn't log any errors when they occur.

As I am guessing its because ELMAH only logs unhandled errors and the [HandleError] attribute is handling the error so thus no need to log it.

How do I modify or how would I go about modifying the attribute so ELMAH can know that there was an error and log it.
 
I'm asking... ELMAH gets bypassed when using the handle error attribute meaning it won't see that there was an error because it was handled already by the attribute... What I am asking is there a way to make ELMAH see the error and log it even though the attribute handled it...I searched around and don't see any methods to call to force it to log the error.
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Updated on 07-Oct-2014
Royce Roy

Royce Roy

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1 Answers

Anonymous User

Anonymous User

07-Oct-2014

You can subclass HandleErrorAttribute and override its OnException member (no need to copy) so that it logs the exception with ELMAH and only if the base implementation handles it. The minimal amount of code you need is as follows.

using System.Web.Mvc;
        using Elmah;
 
        publicclassHandleErrorAttribute : System.Web.Mvc.HandleErrorAttribute
        {
            publicoverridevoid OnException(ExceptionContext context)
            {
                base.OnException(context);
                if (!context.ExceptionHandled) 
                    return;
                var httpContext = context.HttpContext.ApplicationInstance.Context;
                var signal = ErrorSignal.FromContext(httpContext);
                signal.Raise(context.Exception, httpContext);
            }
        }

The base implementation is invoked first, giving it a chance to mark the exception as being handled. Only then is the exception signaled. The above code is simple and may cause issues if used in an environment where the HttpContext may not be available, such as testing. As a result, you will want code that is that is more defensive (at the cost of being slightly longer)

using System.Web;
        using System.Web.Mvc;
        using Elmah;
 
        publicclassHandleErrorAttribute : System.Web.Mvc.HandleErrorAttribute
        {
            publicoverridevoid OnException(ExceptionContext context)
            {
                base.OnException(context);
                if (!context.ExceptionHandled       // ifunhandled, will be logged anyhow
                    ||TryRaiseErrorSignal(context) // prefer signaling,if possible
                    ||IsFiltered(context))         // filtered? return;
 
                LogException(context);
            }
 
            privatestaticbool TryRaiseErrorSignal(ExceptionContext context)
            {
                var httpContext = GetHttpContextImpl(context.HttpContext);
                if (httpContext == null)
                    returnfalse;
                var signal = ErrorSignal.FromContext(httpContext);
                if (signal == null)
                    returnfalse;
                signal.Raise(context.Exception,httpContext);
                returntrue;
            }
 
            privatestaticbool IsFiltered(ExceptionContext context)
            {
                var config = context.HttpContext.GetSection("elmah/errorFilter")
                                as ErrorFilterConfiguration;
 
                if (config == null)
                    returnfalse;
 
                var testContext = new ErrorFilterModule.AssertionHelperContext(
                                      context.Exception, 
                                      GetHttpContextImpl(context.HttpContext));
                return config.Assertion.Test(testContext);
            }
 
            privatestaticvoid LogException(ExceptionContext context)
            {
                var httpContext = GetHttpContextImpl(context.HttpContext);
                var error = new Error(context.Exception, httpContext);
                ErrorLog.GetDefault(httpContext).Log(error);
            }
 
            privatestaticHttpContext GetHttpContextImpl(HttpContextBase context)
            {
                return context.ApplicationInstance.Context;
            }
        }

This second version will try to use error signaling from ELMAH first, which involves the fully configured pipeline like logging, mailing, filtering and what have you. Failing that, it attempts to see whether the error should be filtered. If not, the error is simply logged. This implementation does not handle mail notifications. If the exception can be signaled then a mail will be sent if configured to do so.

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