Controller to Return an Error Message Instead of a View?

Question

I'm fairly new to ASP.NET MVC and am not sure how best to handle the following situation.

A method in my controller needs to load some data based on an ID argument. Under normal circumstances, this ID argument will be set to a valid ID of an entity within my database. I construct some data and place it in ViewBag, which the view uses to render the page.

However, I would like some basic error handling just in case the ID argument is not valid. Although I could write a bunch of error handling code in the view, it would be much simpler not to display the view if there is a major misuse or malfunction of the site.

Is there a way the controller could simply return a "Item not found" string or something like that, and display that rather than the normal view? Or perhaps someone can suggest a better idea?

Answer 1

if (itemId == null)
{
    return Content("Item not found");
}

Or if you want to return an HTTP 404 instead:

throw new HttpException(404, "Item Not Found");

Answer 2

In case fetching model from database (as described in Darin's answer) is somehow complicated and cannot be made generic, this is how I deal with resources not found.

Implement your base controller

    public abstract class MyBaseController : Controller
    {
        [NonAction]
        protected virtual void EnsureResourceFound(object resource)
        {
            if (resource == null)
            {
                HttpStatusCode statusCode = HttpStatusCode.NotFound;
                throw new HttpException((int)statusCode, statusCode.ToString());
            }
        }
    }

And in derived controllers - use that method

    [HttpGet]
    public virtual ActionResult Edit(int id)
    {
        SomeModel model = null;
        EnsureResourceFound(model = _someModelService.Get(id));
        return View(question);
    }

And what will you do with resulting http exception, return custom view, log the error, depends on configured HandleErrorAttribute.

Answer 3

You can do it by simply throwing exception from the Controller.

You need to write following code and need to add ErrorController and it's respective view.

Global.asax

Exception exception = Server.GetLastError();

Response.Clear();

HttpException httpException = exception as HttpException;

//Add controller name
RouteData routeData = new RouteData();
routeData.Values.Add("controller", "Error");

//we will add controller's action name 
routeData.Values.Add("action", "Index");

// Pass exception details to the target error View.
routeData.Values.Add("error", exception.Message);

// Clear the error on server.
Server.ClearError();

// Call target Controller and pass the routeData.
IController errorController = new ErrorController();
errorController.Execute(new RequestContext(new HttpContextWrapper(Context), routeData));


//and throw the exception from the Controller ny simply writing
throw new Exception()

ErrorController:

public class ErrorController : BaseController
    {
        #region Function Declaration
        /// <summary>
        /// Shows application error
        /// </summary>
        /// <param name="error">error description</param>
        public ActionResult Index(string error)
        {
            ViewBag.Description = Resources.ErrorMessage.GeneralError;
            if (string.IsNullOrEmpty(error))
            {
                ViewBag.DetailError = error;
            }
            else
            {
                ViewBag.DetailError = string.Empty;
            }

            return View("ErrorIndex");
        }
        #endregion
    }

Another Approach :

If you want to write a view for a particular error than you have to write followig code. You have to just add DivByZero view.

    [HandleError(View = "DivByZero", ExceptionType = typeof(System.DivideByZeroException))]
    public ActionResult About()
    {
        List<Alok> alokList = new List<Alok>();
        var al = from aa in alokList.Distinct()
                 select aa;

        ViewData["Errorname"] = "Divide By Zero Exception";
        ViewBag.ErrorName = "Divide By Zero Exception";
        //throw new DivideByZeroException();

        return View();
    }

DivByZero View :

@model System.Web.Mvc.HandleErrorInfo
@{
    ViewBag.Title = "Error";
    Layout = "~/Views/Shared/_Layout.cshtml";
}
@*<h2>
    @ViewData["Errorname"].ToString()
    @ViewBag.ErrorName</h2>*@
<p>
    Controller : @Model.ControllerName
</p>
<p>
    Action : @Model.ActionName
</p>
<p>
    Error Message : @Model.Exception
</p>

Answer 4

public ActionResult Foo(int id)
{
    MyModel model = ...
    if (model == null)
    {
        return HttpNotFound();
    }
    return View(model);
}

And since writing this same code over and over again in your actions could quickly become boring a better solution is to write a custom model binder which will fetch the model from the database and if not found will simply throw a new HttpException and set the status code to 404. Then your controller action will simply look like this:

public ActionResult Foo(MyModel model)
{
    return View(model);
}

and the model binder itself:

public class MyModelBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        var id = bindingContext.ValueProvider.GetValue("id");
        if (id == null)
        {
            throw new HttpException(404, "Not found");
        }

        MyModel model = FetchTheModel(id.AttemptedValue);
        if (model == null)
        {
            throw new HttpException(404, "Not found");
        }

        return model;
    }

    private MyModel FetchTheModel(string id)
    {
        throw new NotImplementedException();
    }
}

This model binder could obviously be made more generic.