asp.net mvc - Is it correct way to use ModelState.Remove to deal with ModelState?

Question

Im working on a big MVC3 web application and have an annoyance regarding the ModelState.IsValid method.

ModelState is being used in nearly all of my controllers so to validate the data being posted. The views are all based on ViewModels which contain different classes and these classes obviously contain properties which could be marked as [Required].

The problem i am having is the required properties are sometimes not required and im having to use the ModelState.Remove method so that ModelState.IsValid becomes true.

My question is by using ModelState.Remove, is this the correct way of doing things or is there a more efficient approach.

Answer 1

Here's my solution - a RemoveFor() extension method on ModelState, modelled after MVC HTML helpers:

    public static void RemoveFor<TModel>(this ModelStateDictionary modelState, 
                                         Expression<Func<TModel, object>> expression)
    {
        string expressionText = ExpressionHelper.GetExpressionText(expression);

        foreach (var ms in modelState.ToArray())
        {
            if (ms.Key.StartsWith(expressionText + ".") || ms.Key == expressionText)
            {
                modelState.Remove(ms);
            }
        }
    }

Here's how it's used :

if (model.CheckoutModel.ShipToBillingAddress == true) 
{
    // REUSE BILLING ADDRESS FOR SHIPPING ADDRESS
    ShoppingCart.ShippingAddress = ShoppingCart.BillingAddress;

    // REMOVE MODELSTATE ERRORS FOR SHIPPING ADDRESS
    ModelState.RemoveFor<SinglePageStoreModel>(x => model.CheckoutModel.ShippingAddress);
}

So in answer to your question I believe there are definitely use-cases where this is the right way to do it, and a strongly typed helper like this makes it much nicer to look at - and easier to justify if you're concerned about lots of magic strings.