Question

I have read articles on exception handling in ASP.NET MVC. I want to make sure I am doing right by presenting it briefly. Could anyone please comment.

1. Catch the exceptions in controller actions, if necessary.

   [HttpPost]
   public ActionResult Insert()
   {
       try
       {
   
       }
       catch
       {
           //ModelState.Error -> display error msg to the user.
       }
   }
   

2. Override the “OnException” method of controller in basecontroller and “log” the exceptions raised in step 1 and other MVC exceptions

3. Logged the global exceptions in application_onerror.

Answer 1

I would definitely recommend ELMaH instead of writing this code yourself, and also over Log4Net for your MVC apps. I personally avoid any exception handling, unless I have a specific functional response to it. In this way, I don’t “eat” any of the errors that an application-wide tool such as ELMaH will handle gracefully for me.

ELMaH also has nice built-in web reporting, and there are third-party tools specifically for ELMaH that can give you statistics, e.g. the most frequent errors.

You might start with a custom error redirect…

<customErrors defaultRedirect="~/site/error" mode="RemoteOnly">
  <error statusCode="404" redirect="~/site/notfound" />
</customErrors>

…to a controller that is aware you are using ELMaH…

public virtual ActionResult Error() {
    System.Collections.IList errorList = new System.Collections.ArrayList();
    ErrorLog.GetDefault(System.Web.HttpContext.Current).GetErrors(0, 1, errorList);
    ErrorLogEntry entry = null;
    if (errorList.Count > 0) {
        entry = errorList[0] as Elmah.ErrorLogEntry;
    }
    return View(entry);
}

…backed by a view that helps the visitor get the specific error ID to you:

@model Elmah.ErrorLogEntry

@if (Context.User.Identity.IsAuthenticated) {
    <p>Since you are signed in, we've noted your contact information,
    and may follow up regarding this to help improve our product.</p>
} else {
    <p>Since you aren't signed in, we won't contact you regarding this.</p> 
}
<p>Error ID: @Model.Id</p>

I also notice this is an HttpPost in this example. If you are doing AJAX, then you’ll want to handle errors for those in a unique way. Pick a standard response you can send to browsers that all of your AJAX code handles gracefully. Perhaps by displaying the ELMaH error ID in a javascript alert (as a simple example).

I also handle a few special types of AJAX errors via Global.asax:

protected void Application_EndRequest()
{
    if (Context.Response.StatusCode == 302 &&
        Context.Request.Headers["X-Requested-With"] == "XMLHttpRequest")

HandleErrorAttribute is a nice feature, but it is well-known that there is extra work to use it in conjunction with ELMaH. How to get ELMAH to work with ASP.NET MVC [HandleError] attribute?