Question

I have forms posting data from instances of a particular abstract class:

public abstract class IRestriction
{
    public string Name {get; set;}
    public abstract IModelBinder GetBinder();
}

The concrete type and PartialView are determined at runtime:

IRestriction restriction = (IRestriction)Activator.CreateInstance(Type.GetType(restriction.restriction_class));

The appropriate partial view is then rendered correctly.

When the form is sent back the type is inferred correctly and activated the same way.

However, I haven’t been able to get UpdateModel to bind to the concrete implementation.

How do I get the Model to bind to the concrete type instead of the interface?

Things I’ve tried:

I’ve set the ModelBinderAttribute on the concrete class but it is being ignored.

[ModelBinder(typeof(MyCustomModelBinder))]
public class ConcreteRestriction : IRestriction

I’ve cleared all the ModelBinders and added only the binder from the interface.

Binders.Clear();
Binders.Add(item.GetType(), item.GetBinder());

None of these is working.

Whats the best way to accomplish what I’m trying to do?

Is ModelBinderAttribute being ignored in error?

** ———————-UPDATE———————-**

Here is a solution for anyone else struggling with the same issue who happens to run across this.

The following class inherits Controller. Inherit it and call UpdateModelDynamic()/TryUpdateModelDynamic()

public class DynamicTypeController : Controller
{
    internal static bool IsPropertyAllowed(string propertyName, string[] includeProperties, string[] excludeProperties)
    {
        // We allow a property to be bound if its both in the include list AND not in the exclude list.
        // An empty include list implies all properties are allowed.
        // An empty exclude list implies no properties are disallowed.
        bool includeProperty = (includeProperties == null) || (includeProperties.Length == 0) || includeProperties.Contains(propertyName, StringComparer.OrdinalIgnoreCase);
        bool excludeProperty = (excludeProperties != null) && excludeProperties.Contains(propertyName, StringComparer.OrdinalIgnoreCase);
        return includeProperty && !excludeProperty;
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model) where TModel : class
    {
        return TryUpdateModelDynamic(model, null, null, null, ValueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, string prefix) where TModel : class
    {
        return TryUpdateModelDynamic(model, prefix, null, null, ValueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, string[] includeProperties) where TModel : class
    {
        return TryUpdateModelDynamic(model, null, includeProperties, null, ValueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, string prefix, string[] includeProperties) where TModel : class
    {
        return TryUpdateModelDynamic(model, prefix, includeProperties, null, ValueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, string prefix, string[] includeProperties, string[] excludeProperties) where TModel : class
    {
        return TryUpdateModelDynamic(model, prefix, includeProperties, excludeProperties, ValueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, IValueProvider valueProvider) where TModel : class
    {
        return TryUpdateModelDynamic(model, null, null, null, valueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, string prefix, IValueProvider valueProvider) where TModel : class
    {
        return TryUpdateModelDynamic(model, prefix, null, null, valueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, string[] includeProperties, IValueProvider valueProvider) where TModel : class
    {
        return TryUpdateModelDynamic(model, null, includeProperties, null, valueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, string prefix, string[] includeProperties, IValueProvider valueProvider) where TModel : class
    {
        return TryUpdateModelDynamic(model, prefix, includeProperties, null, valueProvider);
    }

    protected internal bool TryUpdateModelDynamic<TModel>(TModel model, string prefix, string[] includeProperties, string[] excludeProperties, IValueProvider valueProvider) where TModel : class
    {
        if (model == null)
        {
            throw new ArgumentNullException("model");
        }
        if (valueProvider == null)
        {
            throw new ArgumentNullException("valueProvider");
        }

        Predicate<string> propertyFilter = propertyName => IsPropertyAllowed(propertyName, includeProperties, excludeProperties);
        IModelBinder binder = Binders.GetBinder(model.GetType());

        ModelBindingContext bindingContext = new ModelBindingContext()
        {
            ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, model.GetType()),
            ModelName = prefix,
            ModelState = ModelState,
            PropertyFilter = propertyFilter,
            ValueProvider = valueProvider
        };
        binder.BindModel(ControllerContext, bindingContext);
        return ModelState.IsValid;
    }


    protected internal void UpdateModelDynamic<TModel>(TModel model) where TModel : class
    {
        UpdateModelDynamic(model, null, null, null, ValueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, string prefix) where TModel : class
    {
        UpdateModelDynamic(model, prefix, null, null, ValueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, string[] includeProperties) where TModel : class
    {
        UpdateModelDynamic(model, null, includeProperties, null, ValueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, string prefix, string[] includeProperties) where TModel : class
    {
        UpdateModelDynamic(model, prefix, includeProperties, null, ValueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, string prefix, string[] includeProperties, string[] excludeProperties) where TModel : class
    {
        UpdateModelDynamic(model, prefix, includeProperties, excludeProperties, ValueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, IValueProvider valueProvider) where TModel : class
    {
        UpdateModelDynamic(model, null, null, null, valueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, string prefix, IValueProvider valueProvider) where TModel : class
    {
        UpdateModelDynamic(model, prefix, null, null, valueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, string[] includeProperties, IValueProvider valueProvider) where TModel : class
    {
        UpdateModelDynamic(model, null, includeProperties, null, valueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, string prefix, string[] includeProperties, IValueProvider valueProvider) where TModel : class
    {
        UpdateModelDynamic(model, prefix, includeProperties, null, valueProvider);
    }

    protected internal void UpdateModelDynamic<TModel>(TModel model, string prefix, string[] includeProperties, string[] excludeProperties, IValueProvider valueProvider) where TModel : class
    {
        bool success = TryUpdateModelDynamic(model, prefix, includeProperties, excludeProperties, valueProvider);
        if (!success)
        {
            string message = String.Format("The model of type '{0}' could not be updated.", model.GetType().FullName);
            throw new InvalidOperationException(message);
        }
    }

}

Answer 1

I think it’s a bug, but the ASP.NET MVC team disagrees. Model binding looks at the static, compile-time type of the model. I don’t like it, but that’s how it is.