ASP.NET MVC - Complex model validation

Question

I have a ViewModel class like this:

class CaseModel {
    public Boolean     ClientPresent { get; set; }
    public ClientModel Client        { get; set; }
}

class ClientModel {
    [Required]
    public String      FirstName     { get; set; }
    [Required]
    public String      LastName      { get; set; }
}

The view page consists of a <input type="checkbox" name="ClientPresent" /> and a Html.EditorFor( m => m.Client ) partial view.

The idea being that when the user if providing information about a case (a business-domain object) that they can choose to not specify any information about the client (another biz object) by unchecking the ClientPresent box.

I want ASP.NET MVC to not perform any validation of the child ClientModel object - however the CaseModel.Client property is automatically populated when a form is POSTed back to the server, but because FirstName and LastName aren't (necessarily) provided by the user it means it fails the [Required] validation attributes, consequently ViewData.ModelState.IsValid returns false and the user gets a validation error message.

How can I get it so CaseModel.Client will not be validated if CaseModel.ClientPresent is false?

Note that ClientModel is a fully independent ViewModel class and is used elsewhere in the application (such as in the ClientController class which lets the user edit individual instances of Clients).

Answer 1

I recognise that my problem is not to do with binding but actually with validation: by keeping the values it means the same form fields will be populated when the user reloads the page, I just needed the validation messages to be discarded as they weren't applicable.

To that end I realised I can perform the model property validation, but then use some custom logic to remove the validation messages. Here's something similar to what I did:

public class CaseModel {
    public void CleanValidation(ModelStateDictionary dict) {
        if( this.ClientPresent ) {
            dict.Keys.All( k => if( k.StartsWith("Client") dict[k].Errors.Clear() );
        }
    }
}

(Obviously my actual code is more robust, but you get the general idea)

The CleanValidation method is called directly by the controller's action method:

public void Edit(Int64 id, CaseModel model) {
    model.CleanValidation( this.ModelState );
}

I can probably tidy this up by adding CleanValidation as a method to a new interface IComplexModel and having a new model binder automatically call this method so the controller doesn't need to call it itself.

Update:

I have this interface which is applied to any ViewModel that requires complicated validation:

public interface ICustomValidation {

    void Validate(ModelStateDictionary dict);
}

In my original example, CaseModel now looks like this:

 public class CaseClientModel : ICustomValidation {

      public Boolean ClientIsNew { get; set; } // bound to a radio-button
      public ClientModel ExistingClient { get; set; } // a complex viewmodel used by a partial view
      public ClientModel NewClient { get; set; } // ditto

      public void Validate(ModelStateDictionary dict) {

          // RemoveElementsWithPrefix is an extension method that removes all key/value pairs from a dictionary if the key has the specified prefix.
          if( this.ClientIsNew ) dict.RemoveElementsWithPrefix("ExistingClient");
          else                   dict.RemoveElementsWithPrefix("NewClient");
      }
 }

The validation logic is invoked by OnActionExecuting in my common BaseController class:

protected override void OnActionExecuting(ActionExecutingContext filterContext) {
    base.OnActionExecuting(filterContext);
    if( filterContext.ActionParameters.ContainsKey("model") ) {

        Object                    model = filterContext.ActionParameters["model"];
        ModelStateDictionary modelState = filterContext.Controller.ViewData.ModelState; // ViewData.Model always returns null at this point, so do this to get the ModelState.

        ICustomValidation modelValidation = model as ICustomValidation;
        if( modelValidation != null ) {
            modelValidation.Validate( modelState );
        }
    }
}

Answer 2

You have to create a custom model binder by inheriting from the default model binder.

  public class CustomModelBinder: DefaultModelBinder
  {
    protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor)
    {
      if (propertyDescriptor.Name == "Client")
      {
          var clientPresent = bindingContext.ValueProvider.GetValue("ClientPresent");

          if (clientPresent == null || 
                string.IsNullOrEmpty(clientPresent.AttemptedValue))
              return;
      }

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

Global.asax.cs

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