Question

I’ve been directed to an very nice article that shows how to create a Custom Validator from start to finish. My only problem is that this only works on single fields:
http://haacked.com/archive/2009/11/19/aspnetmvc2-custom-validation.aspx

What if I need to validate against 2 or more properties in my Model? How can I pass my entire Model into the Validator?

NOTE: To be clear, I really don’t want to have to resort to validating the entire model on post back… that would defeat the purpose of this method.

Answer 1

You need to use a custom validate attribute and decorate your model with it, not individual properties:

[AttributeUsageAttribute(AttributeTargets.Class, AllowMultiple = true, Inherited = false)]
public class MyCustomValidatorAttribute : ValidationAttribute 
{
    public override bool IsValid(object value) 
    {
        // value here will be the model instance you could cast
        // and validate properties
        return true;
    }
}

and then decorate your model with it:

[MyCustomValidator]
public class MyViewModel
{
    public string Prop1 { get; set; }
    public string Prop2 { get; set; }
}

As an alternative to data annotations to perform validation I would more than strongly recommend you FluentValidation.NET. It also has great integration with ASP.NET MVC.