Conditionally validating portions of an ASP.NET MVC Model with DataAnnotations?

Question

I have certain panels on my page that are hidden under certain circumstances.

For instance I might have a 'billing address' and 'shipping address' and I dont want to validate 'shipping address' if a 'ShippingSameAsBilling' checkbox is checked.

I am trying to use the new DataAnnotations capabilities of ASP.NET MVC 2 (preview 1) to achieve this.

I need to prevent validation of the 'shipping address' when it is not displayed and need to find the way way to achieve this. I am talking mainly server side as opposed to by using jquery.

How can I achieve this? I have had several ideas, related to custom model binding but my current best solution is below. Any feedback on this method?

Answer 1

For the CheckoutModel I am using this approach (most fields hidden):

[ModelBinder(typeof(CheckoutModelBinder))]
public class CheckoutModel : ShoppingCartModel
{        
    public Address BillingAddress { get; set; }
    public Address ShippingAddress { get; set; }
    public bool ShipToBillingAddress { get; set; }
}

public class Address
{
    [Required(ErrorMessage = "Email is required")]
    public string Email { get; set; }

    [Required(ErrorMessage = "First name is required")]
    public string FirstName { get; set; }

    [Required()]
    public string LastName { get; set; }

    [Required()]
    public string Address1 { get; set; }
}

The custom model binder removes all ModelState errors for fields beginning with 'ShippingAddress' if it finds any. Then 'TryUpdateModel()' will return true.

    public class CheckoutModelBinder : DefaultModelBinder
    {
        protected override void OnModelUpdated(ControllerContext controllerContext,
                                               ModelBindingContext bindingContext) {

            base.OnModelUpdated(controllerContext, bindingContext);

            var model = (CheckoutModel)bindingContext.Model;

            // if user specified Shipping and Billing are the same then 
            // remove all ModelState errors for ShippingAddress
            if (model.ShipToBillingAddress)
            {
                var keys = bindingContext.ModelState.Where(x => x.Key.StartsWith("ShippingAddress")).Select(x => x.Key).ToList();
                foreach (var key in keys)
                {
                    bindingContext.ModelState.Remove(key);
                }
            }
        }    
    }

Any better solutions?

Answer 2

http://bradwilson.typepad.com/blog/2009/04/dataannotations-and-aspnet-mvc.html

Answer 3

I can see your predicament. I'm looking for other validation solutions also with regard to complex validation rules that might apply to more than one property on a given model object or even many properties from different model objects in a object graph (if your unlucky enough to be validating linked objects like this).

The limitation of the IDataErrorInfo interface is that a model object satisfies the valid state simply when none of the properties have errors. This is to say that a valid object is one where all of it's properties are also valid. However, i may have a situation where if property A, B and C are valid - then the whole object is valid.. but also if property A is not valid but B and C are, then the object satisfies validity. I simply have no way of describing this condition/rule with the IDataErrorInfo interface / DataAnnotations attributes.

So i found this delegate approach. Now many of the helpful advancements in MVC didn't exist at the time of writing this article but the core concept should help you. Rather than using attributes to define the validation conditions of an object we create delegate functions that validate more complex requirements and because they're delegated we can re-use them. Sure it's more work, but the use of delegates means that we should be able to write validation rule code once and store all the validation rules in the one place (maybe service layer) and (the kool bit) even use the MVC 2 DefaultModelBinder to invoke the validation automatically (without heaps of checking in our controller actions - like Scott's blog says we can do with DataAnnotations. Refer to the last paragraph before the 'Strongly Typed UI Helpers' heading)!

I'm sure you can beef the approach suggested in the above article up a little with anonymous delegates like Func<T> or Predicate<T> and writing custom code blocks for the validation rules will enable cross-property conditions (for example the condition you referred to where if your ShippingSameAsBilling property is true then you can ignore more rules for the shipping address, etc).

DataAnnotations serves to make simple validation rules on objects really easy with very little code. But as your requirements develop you will need to validate on more complex rules. The new virtual methods in the MVC2 model binder should continue to provide us with ways of integrating our future validation inventions into the MVC framework.

Answer 4

Make sure the fields you don't want validated are not posted to the action. We only validate the fields that were actually posted.

Edit: (by questioner)

This behavior has changed in MVC2 RC2 :

Default validation system validates entire model The default validation system in ASP.NET MVC 1.0 and in previews of ASP.NET MVC 2 prior to RC 2 validated only model properties that were posted to the server. In ASP.NET MVC 2, the new behavior is that all model properties are validated when the model is validated, regardless of whether a new value was posted. Applications that depend on the ASP.NET MVC 1.0 behavior may require changes. For more information about this change, see the entry Input Validation vs. Model Validation in ASP.NET MVC on Brad Wilson’s blog.

Answer 5

This isn't related to DataAnnotations but have you looked at the Fluent Validation project? It gives you fine grain control over your validation and if you have object-to-object validation an aggregate object of the two objects will get you going.

Also it seems to have been build with MVC in mind but it also has its own "runtime" so that you can use it in other .NET applications as well which is another bonus in my book.

Answer 6

For the more complex cases I moved away from simple DataAnnotations to the following: Validation with visitors and extension methods.

If you want to make use of your DataAnnotations you would replace something like the following:

public IEnumerable<ErrorInfo> BrokenRules (Payment payment)
{   
    // snip... 
    if (string.IsNullOrEmpty (payment.CCName))
    {
      yield return new ErrorInfo ("CCName", "Credit card name is required");
    }
}

with a method to validate a property by name via DataAnnotations (which I don't have atm).

Answer 7

I created a partial model binder that only validates the keys that were submitted. For security reasons (if I was going to take this a step farther) I'd create a data annotation attribute that marks which fields are allowed to be excluded from a model. Then, OnModelUpdated check field attributes to ensure there is no undesired underposting going on.

public class PartialModelBinder : DefaultModelBinder
{
    protected override void OnModelUpdated(ControllerContext controllerContext, 
        ModelBindingContext bindingContext)
    {
        // default model binding to get errors
        base.OnModelUpdated(controllerContext, bindingContext);

        // remove errors from filds not posted
        // TODO: include request files
        var postedKeys = controllerContext.HttpContext.Request.Form.AllKeys;
        var unpostedKeysWithErrors = bindingContext.ModelState
            .Where(i => !postedKeys.Contains(i.Key))
            .Select(i=> i.Key).ToList();
        foreach (var key in unpostedKeysWithErrors)
        {
            bindingContext.ModelState.Remove(key);
        }
    }    
}