Model Validation / ASP.NET MVC 3 - Conditional Required Attribute

Question

I'm having trouble with my ASP.NET MVC 3 application. I have 2 propertiesin my model whereby I only want 1 of them required in my view based on whichever one is empty. So for example, if I enter a phone number then email is no longer required and vice versa, but if I leave both empty, then either 1 should be required, below is my model:

[Display(Name = "Contact Phone Number:")]
[MaxLength(150)]
public string ContactPhoneNumber { get; set; }

[Display(Name = "Contact Email Address:")]
[MaxLength(100)]
public string ContactEmailAddress { get; set; }

Would I need to create a custom attribute to validate my model and if so, how would I achieve this?

Answer 1

You can implement IValidatableObject on your class and provide a Validate() method that implements your custom logic. Combine this with custom validation logic on the client if you prefer to ensure that one is supplied. I find this easier than implementing an attribute.

public class ContactModel : IValidatableObject
{
   ...

   public IEnumerable<ValidationResult> Validate( ValidationContext context )
   {
        if (string.IsNullOrWhitespace( ContactPhoneNumber ) 
            && string.IsNullOrWhitespace( ContactEmailAddress ))
        {
             yield return new ValidationResult( "Contact Phone Number or Email Address must be supplied.", new [] { "ContactPhoneNumber", "ContactEmailAddress" } );
        }
   }
}

To get everything working at client side you'll need to add the following script to your view:

<script type="text/javascript">
$(function() {
    $('form').validate(); 
    $('form').rules('add', { 
        "ContactPhoneNumber": { 
            depends: function(el) { return !$('#ContactEmailAddress').val(); } 
        } 
    });
});
</script>