DataAnnotations "NotRequired" attribute

Question

I've a model kind of complicated.

I have my UserViewModel which has several properties and two of them are HomePhone and WorkPhone. Both of type PhoneViewModel. In PhoneViewModel I have CountryCode, AreaCode and Number all strings. I want to make the CountryCode optional but AreaCode and Number mandatory.

This works great. My problem is that in the UserViewModel WorkPhone is mandatory, and HomePhone is not.

Is there anyway I can dissable Require attributs in PhoneViewModel by setting any attributes in HomeWork property?

I've tried this:

[ValidateInput(false)]

but it is only for classes and methods.

Code:

public class UserViewModel
{
    [Required]
    public string Name { get; set; }

    public PhoneViewModel HomePhone { get; set; }

    [Required]    
    public PhoneViewModel WorkPhone { get; set; }
}

public class PhoneViewModel
{
    public string CountryCode { get; set; }

    public string AreaCode { get; set; }

    [Required]
    public string Number { get; set; }
}

Answer 1

[UPDATED on 5/24/2012 to make the idea more clear]

I'm not sure this is the right approach but I think you can extend the concept and can create a more generic / reusable approach.

In ASP.NET MVC the validation happens at the binding stage. When you are posting a form to the server the DefaultModelBinder is the one that creates model instances from the request information and add the validation errors to the ModelStateDictionary.

In your case, as long as the binding happens with the HomePhone the validations will fire up and I think we can't do much about this by creating custom validation attributes or similar kind.

All I'm thinking is not to create model instance at all for HomePhone property when there are no values available in the form (the areacode, countrycode and number or empty), when we control the binding we control the validation, for that, we have to create a custom model binder.

In the custom model binder we are checking if the property is HomePhone and if the form contains any values for it's properties and if not we don't bind the property and the validations won't happen for HomePhone. Simply, the value of HomePhone will be null in the UserViewModel.

  public class CustomModelBinder : DefaultModelBinder
  {
      protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor)
      {
        if (propertyDescriptor.Name == "HomePhone")
        {
          var form = controllerContext.HttpContext.Request.Form;

          var countryCode = form["HomePhone.CountryCode"];
          var areaCode = form["HomePhone.AreaCode"];
          var number = form["HomePhone.Number"];

          if (string.IsNullOrEmpty(countryCode) && string.IsNullOrEmpty(areaCode) && string.IsNullOrEmpty(number))
            return;
        }

        base.BindProperty(controllerContext, bindingContext, propertyDescriptor);
      }
  }

Finally you have to register the custom model binder in global.asax.cs.

  ModelBinders.Binders.Add(typeof(UserViewModel), new CustomModelBinder());

So now of you have an action that takes UserViewModel as parameter,

 [HttpPost]
 public Action Post(UserViewModel userViewModel)
 {

 }

Our custom model binder come into play and of form doesn't post any values for the areacode, countrycode and number for HomePhone, there won't be any validation errors and the userViewModel.HomePhone is null. If the form posts atleast any one of the value for those properties then the validation will happen for HomePhone as expected.