Monthly Archives: June 2013

Building Client (JavaScript) Custom Validation in ASP.NET MVC 4 using jQuery


I was recently asked by some students of mine how exactly is client custom validation done in ASP.NET MVC (4). I did this once before unobtrusive validation and jQuery in ASP.NET MVC 2.0 but then I lost contact with the implementation details.

In ASP.NET MVC 4 (this started in MVC 3) there is jQuery unobtrusive validation that works hand-in-hand with Data Annotations (a set of validation attributes that can decorate properties or even (view)model classes). I just remembered that you need to create a ValidationAttribute subclass and also implement IClientValidatable on it. Also you must decorate a property of the (View)Model with this attribute.

On the client side you need to write JavaScript code that provides a validation adapter and a validation function.

Let’s suppose we’d want to create an URL shortening service and on the “Add URL” page we’d have three fields :
- Original URL (textbox)
- Use custom slug (checkbox)
- Custom slug (textbox)

The “Original URL” textbox would be mandatory and the input format should be of a fully-qualified URL (for example “” :P )

The custom slug textbox would be mandatory ONLY if the “Use custom slug” checkbox would be checked. This is the tough part since validating this field requires knowledge of another field’s value (the checkbox in this case). And by tough I mean having to write actual code because there is no out-of-the-box validator for this (not on the server-side nor on the client-side).

This small tutorial will asume that you have knowledge of the ASP.NET MVC platform and C#. I will not go into detail on matters such as what is the MVC pattern, what is the controller, view etc.


Implementation – server side

Let’s start by creating a new ASP.NET MVC 4 web project (select “Internet site” template).
We’ll create a UrlController controller with an action called Add :

using System.Web.Mvc;

namespace MVC4_jQuery_Unobtrusive_Custom_Validation.Controllers
    public class UrlController : Controller
        public ActionResult Add()
            return View();

        public ActionResult Add(AddUrlViewModel userInput)
            if (ModelState.IsValid)
                // store the data
                // ...
                return RedirectToAction("Index", "Home");
            return View();

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Bing it on, Reactive Extensions! – story, code and slides

I held a presentation at UBISOFT Buchares headquarters for the RONUA local programmers user group recently as I’ve announced earlier.
Here’s the contents, step-by-step, final code and slides.

————- [scroll way down for the downloads]

I was recently tasked with rewriting an app component by leveraging Reactive Extensions. I knew little about Rx (the short form of Reactive Extensions) and all I remembered was that it has two interfaces IObservable and IObserver and it seemed dull at that time.

Basically the component enables search without needing to hit ENTER or a “Go!” button, although provides for these. After the user finishes typing an async request goes to the data store and searches for the phrase entered and fetches the results. In the original implementation the component used a lot of timers, event handlers, private fields all making up a nice spaghetti bowl of code.

Let’s do this step by step and see how our little (demo) app develops. Fire up Visual Studio 2012 and start a new WPF project (.NET 4.5 preferrably). The very next thing we’ll install Rx. Right click on the project in the Solution Explorer and select “Manage NuGet Packages” (you can also use the Package Manager Console if you like it better). Search online for “Reactive Extensions”.

In the result lists (this requires a functional internet connection) select ‘Reactive Extensions – WPF Helpers‘ (the nice thing about NuGet packages is that it automatically resolves and installs all the dependencies). Accept the license(s) (you know what’s the most common lie told these days? “I have read and accepted the terms of the license” :P ).

In our demo we will use Bing as the data store which we’ll target through our searches (sorry, Google was too difficult to setup, offered less search requests per month and no C# demo code. Thanks Google, thanks again.). In order to do this you will need a Microsoft Account (I guess we all have one these days). Go to and then select “Search API” -> Start now (this will lead you to ). There are paid subscriptions and a free subscription. Hit signup and go through the process (leave a comment if you are unable to go through this process).

In the end you will need to obtain the (Primary) Account Key and the Customer ID. These are available under “My Account” -> Account Information ( ). We’ll use these later so save them. Also, don’t share them with other people because these are your credentials. Also visit “My Data” ( ) and click on “Bing Search API”‘s “Use” link (far right, ). Capture the “URL for current expressed query” : ““. We’ll also need these later.

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