Preferred method for returning exceptions from MVC controller back to ajax call

Question

I've seen multiple ways to return a custom exception from the controller back to an ajax call. I'm wondering what the best practices or preferred methods are so that I can start to standardize all of the ajax calls in my project.

I just want to highlight two ways I've seen of handling ajax exceptions and come to a conclusion about which is "better".

I apologize if there is a post/response that already answers this question, but I searched quite a bit and could not find a definitive answer.

Environment info: using MVC 4, .Net 4.5, jQuery 1.10.2

Method 1:

One example I've seen of handling custom errors is from a response to another post on this site that describes creating a custom error filter. So in this case I would have:

JsonExceptionFilterFilter

public class JsonExceptionFilterAttribute : FilterAttribute, IExceptionFilter
{
    public void OnException(ExceptionContext filterContext)
    {
        if (filterContext.RequestContext.HttpContext.Request.IsAjaxRequest())
        {
            filterContext.HttpContext.Response.StatusCode = 500;
            filterContext.ExceptionHandled = true;
            filterContext.Result = new JsonResult
            {
                Data = new
                {
                    // obviously here you could include whatever information you want about the exception
                    // for example if you have some custom exceptions you could test
                    // the type of the actual exception and extract additional data
                    // For the sake of simplicity let's suppose that we want to
                    // send only the exception message to the client
                    errorMessage = filterContext.Exception.Message
                },
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
            };
        }
    }
}

My controller action would then look like:

[HttpPost]
[JsonExceptionFilter]
public ActionResult MyAction() {

    // do things

    if(some conditional here is false) {
        // the custom exception thrown here will be processed by the JsonExceptionFilter
        // so that the ajax call actually recognizes that an exception occurred.
        throw new CustomException(); 
    }

    return View()
}

You'll then see the HTTP 500 error when looking at Firebug or Chrome devtools. By using this custom error filter, the $.ajax.fail() would actually be hit.

$.ajax({
    type: 'POST',
    url: '/MyAction/MyController',
    data:{ ... }
}).done(function(response) {
    // process a successful response
}).fail(function(xhr) {
    // My custom error thrown in the controller gets caught here
});

Method 2:

The second method I see a lot is to just return a Json object that contains a boolean value for whether or not the request was successful.

[HttpPost]
public ActionResult MyAction() {

    // do stuff

    if(some condition here is false) {
        return Json(new { errorOccurred=true, errorMessage="something failed" });
    }

    // do stuff

    return View()
}

The one annoyance I see with this method is that you're always required to check if the request was successful or not:

$.ajax({
    type: 'POST',
    url: '/MyAction/MyController',
    data:{ ... }
}).done(function(response) {
    if(response.errorOccurred) {
        // display the error message to the user
    }
    else {
        // continue processing the successful response
    }
});

So out of those two methods, which one is typically the preferred or "better" way of doing things? Or is there a third option that is the new standard for handling ajax exceptions? Both ways get the job done, but I do think that implementing the custom filter is cleaner and allows for better debugging.

Thanks in advance for any advice.

Preferred method for returning exceptions from MVC controller back to ajax call

0 Answers0