Using MVC and fluent Nhibernate, how do I validate unique fields on my ViewModel before I bind them to my Domain Object and Save them?

I have a website where I allow users to create new Part records. I'm trying to figure out the best way to validate specific fields for uniqueness. I want to make sure that somebody doesn't try to add a Part with PartNumber 1234 if that PartNumber already exists on a different Part.

The Web Application is using Asp.net MVC with fluent nHibernate for mapping my objects to the database. I'm using Castle validation on my view models for things like ValidateNonEmpty, ValidateRange, etc. Should I use the ValidateSelf method to query the repository to see if that part number already exists? Something doesn't feel right about using my Repository on the ViewModel.

Would it be better for me to place that logic on the controller action? That doesn't seem right because I expect my ViewModel to already be Validated at the point (during ModelBind).

Or maybe its none of the above. Thanks for any help on this one.

UPDATE Ok, not sure if this will help, but here is what my Save action looks like for a typical Create Action in my project:

public ActionResult Create(PartViewModel viewModel)
{
 //I think I'd like to know if its Valid by this point, not on _repository.Save
 if(ModelState.IsValid)
 {
    try
    {
        var part = _partCreateViewModelMap.MapToEntity(viewModel);

        _repository.Save(part);
        return Redirect("~/Part/Details/" + part.Id);
    }
    catch (Exception e)
    {
        // skip on down...
    }
 }

 // return view to edit 
 return View(viewModel);
}

Edit Report

I would say this matters on your architecture. With MVC apps that I have done in the past we abstract away the domain stuff away from the web stuff and naturally we use dependency injection to avoid hard dependencies.

When it comes to validating the model when you are in the act of binding it, yes you could easily use the service, repository, or whatever you have next in your architecture in a ValidateSelf method. I think the question rises of what about that dependency.

If I remember correctly you can create your own custom binder that will use your dependency injection framework to plug-in any services your model needs for validation when you create it, call MVC's default binder to fill in the object, then call into Castle Validation's framework to do the validation. This isn't a fully thought solution, but hopefully it provokes some ideas.

answered 2009-09-23T00:53:51.657

Using MVC and fluent Nhibernate, how do I validate unique fields on my ViewModel before I bind them to my Domain Object and Save them?

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