ASP.NET MVC 3 - Bind model to a List<> that contains different types - asp.net-mvc-3

Question

I'm trying to work out how to bind a model that contains a list of multiple object types to a postback action in ASP.NET MVC 3. I've got the following classes that define a list a vehicle types:
public enum VehicleType
{
Car,
Plane.
Boat
}
public class BaseVehicle
{
public VehicleType VehicleType { get; set; }
public string Name { get; set; }
public int Passengers { get; set; }
}
public class Plane : BaseVehicle
{
public int WingSpan { get; set; }
// -- etc --
}
// Properties omitted
public class Car : BaseVehicle {}
public class Boat : BaseVehicle {}
public class VehiclesViewModel
{
public string Notes { get; set; }
public List<BaseVehicle> Vehicles { get; set; }
}
The above classes are displayed by these views:
<!-- VehiclesView.cshtml - loaded by the controller -->
#model Mvc3Test.Models.VehiclesViewModel
<h2>Vehicles</h2>
#Html.EditorFor(m => m.Notes)
<hr />
#Html.EditorFor(m => m.Vehicles)
<!-- BaseVehicle.cshtml -->
#model BaseVehicle
#using Mvc3Test.Data
#Html.HiddenFor(m => m.VehicleType)
#{
if (Model.VehicleType == VehicleType.Car)
{
Html.RenderPartial("Car", (Car)Model);
}
else if (Model.VehicleType == VehicleType.Plane)
{
Html.RenderPartial("Plane", (Plane)Model);
}
// etc..
}
<-- Plane.cshtml -->
#model Mvc3Test.Data.Plane
<h2>Plane</h2>
<p>Name: #Html.EditorFor(m => m.Name)</p>
<p>Passengers: #Html.EditorFor(m => m.Passengers)</p>
<p>Wingspan: #Html.EditorFor(m => m.WingSpan) metres</p>
<!-- Car.cshtml omitted -->
I don't know it the above is the best way to handle the displaying (especially the if statement within a view), but it works for now. The problem is how to bind back to the viewmodel class. I've tried replacing the Html.TextBorFor() with Html.TextBox() so I can add binding prefixes ("Vehicles.Car" etc..) but there does not seem to be a way of getting the default model binders to determine what kind of class is being represented in the html so the right type can be instantiated.
I think I'll have to write a custom model binder to work it out - is this the right method to use or is there another way I've missed?
Thanks for any help

Answer 1

First of all
if (Model.VehicleType == VehicleType.Car)
{
Html.RenderPartial("Car", (Car)Model);
}
else if (Model.VehicleType == VehicleType.Plane)
{
Html.RenderPartial("Plane", (Plane)Model);
}
Can be omitted with EditorFor.Works just fine.
As for binding back - IMO best way is to create custom model binder.
Example:
public class DerivedTypeModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var typeName = GetVehicleType(bindingContext);
if (typeName != null)
{
var modelType = Type.GetType(typeName);
var targetTypeInstance = Activator.CreateInstance(modelType);
bindingContext = new ModelBindingContext
{
ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => targetTypeInstance, modelType),
ModelState = bindingContext.ModelState,
FallbackToEmptyPrefix = bindingContext.FallbackToEmptyPrefix,
ModelName = bindingContext.FallbackToEmptyPrefix ? string.Empty : bindingContext.ModelName,
ValueProvider = bindingContext.ValueProvider,
};
}
return base.BindModel(controllerContext, bindingContext);
}
private string GetVehicleType(ModelBindingContext bindingContext)
{
var valueResult = bindingContext.ValueProvider.GetValue(bindingContext.ModelName + "." + "VehicleType");
if (valueResult == null && bindingContext.FallbackToEmptyPrefix)
{
valueResult = bindingContext.ValueProvider.GetValue("VehicleType");
}
return valueResult == null ? null : valueResult.AttemptedValue;
}
}