Question

I have an action method without parameters.

The QueryString collection contain all of my values. The keys of the QueryString match my view model properties.

var queryStringValueProvider = new QueryStringValueProvider(ControllerContext);
var providerResult = queryStringValueProvider.GetValue(ValidationKeys.Id); // ?!

var viewModelTypeName = queryString[ValidationKeys.ViewModelType];

var viewModelType = Type.GetType(viewModelTypeName);
var viewModelInstance = providerResult.ConvertTo(viewModelType); // throws an InvalidOperationException

How can I convert the QueryString collection to a view model?
ASP.NET MVC already do this when you just pass the view model into the action method parameters. So what I need is an afterwards model binding using ASP.NET MVC mechanics.

Answer 1

My Controller Action

var viewModelTypeName = queryString[ValidationKeys.ViewModelType];
var viewModelType = Type.GetType(viewModelTypeName);
var instance = Activator.CreateInstance(viewModelType);
UpdateModelUsingQueryString(instance);

UpdateModel

protected internal void UpdateModelUsingQueryString<TModel>(TModel model) where TModel : class
{
    if (model == null) throw new ArgumentNullException("model");

    Predicate<string> propertyFilter = propertyName => new BindAttribute().IsPropertyAllowed(propertyName);
    var binder = Binders.GetBinder(typeof(TModel));

    var bindingContext = new ModelBindingContext()
    {
        ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, model.GetType()),
        ModelState = ModelState,
        PropertyFilter = propertyFilter,
        ValueProvider = new QueryStringValueProvider(ControllerContext)
    };
    binder.BindModel(ControllerContext, bindingContext);
}

The problem was that UpdateModel or TryUpdateModel does not work for object by design.
Both methods use typeof(TModel). But you have to use model.GetType().

Take a look at: Model Binding – Type in External Assembly

Darin Dimitrov gave the right answer 🙂