DRY Remote Validation in ASP.NET MVC 3

Question

I've read David Hayden's great post on MVC 3 Remote validation.

However there is presented what you should do to enable remote (javascript) validation. If the user has javascript disabled the post would still be made even if data is not valid. Therefore a server-side validation should occur.

How could we make this check as DRY (Don't Repeat Yourself) as possible? Of course, including the same check code in the post action as in the remote validation action (or just the same call) can work but I am wondering if a one-liner or something more elegant is available.

Perfectly acceptable answers include "no, it can't be done". :)

Answer 1

It 'can' be done.. but you would need to write your own custom attribute that basically emits for client side and is validated server side. For me I just extract the validation code into a method and check on the server. Something similar came up recently as well:

Prevent form from submitting when using unobtrusive validation in ASP.NET MVC 3

I wonder if one couldnt inherit from the remote attribute and add their own server side code them. hmm.. maybe I'll have to try this.

I would be happy though if someone here said they already did this : )

Answer 2

See my MSDN article How to: Implement Remote Validation in ASP.NET MVC I use the remote client validation code in the HttpPost Create method to test server side when JavaScript is disabled.

[HttpPost]
    public ActionResult Create(CreateUserModel model) {

        // Verify user name for clients who have JavaScript disabled
        if (_repository.UserExists(model.UserName)) {
            ModelState.AddModelError("UserName", ValidationController.GetAltName(model.UserName, _repository));
            return View("Create", model);
        }

Answer 3

I have done this, it's a bit of a long solution, so it's all available on my blog here:

http://www.metaltheater.com/tech/technical/fixing-the-remote-validation-attribute/

I had to create a new subclass of the RemoteAttribute class, create my own custom model binder by inheriting from DefaultModelBinder, and then use reflection to call the validator on the controller.