WebApi2 FromBody RequestMessage of different types - asp.net-web-api

Question

I'm designing an ASP.Net Webapi 2 solution which can possibly receive one of the forms of a request message from the [Frombody] as below.
How should I design the concrete class that will bind to the incoming request message? Any suggestion would be much appreciated.
<?xml version="1.0" encoding="utf-8"?>
<RequestMessage>
<Shapes>
<RectangleInfo></RectangleInfo>
</Shapes>
</RequestMessage>
or
<RequestMessage>
<Shapes>
<CicleInfo></CicleInfo>
</Shapes>
</RequestMessage>
or
<RequestMessage>
<Shapes>
<SquareInfo></SquareInfo>
</Shapes>
</RequestMessage>

Answer 1

Consider using the ModelBinder interface and return an IShape of the correct type: RectangleShape, CicleShape or SquareShape. Your controller method will look something like this when you get done:
public Task<HttpResponseMessage> GetShape(
[ModelBinder] IShape shape = null) { ... }
Your binder will look something like
using System;
using System.Net;
using System.Web.Http.Controllers;
using System.Web.Http.ModelBinding;
/// <summary>Web API ModelBinder for Shape.</summary>
/// <example>
/// At service startup include:
/// config.Services.Insert(typeof(ModelBinderProvider), 0, new SimpleModelBinderProvider(typeof(IShape), new ShapeBinder()));
/// <br/>
/// On controller methods that need a IShape
/// public async Task<HttpResponseMessage> SomeMethod([ModelBinder] IShape shape)
/// </example>
public class ShapeBinder : IModelBinder
{
/// <summary>Create a Shape.</summary>
/// <returns>true if a valid shape . false otherwise.</returns>
public bool BindModel(HttpActionContext actionContext, ModelBindingContext bindingContext)
{
if (bindingContext.ModelType == typeof(IShape))
{
return CreateShape(actionContext, bindingContext);
}
return false;
}
Your class heirarchy will be something like
public abstract class Shape : IShape { .. properties for all shapes ... }
public class SquareShape : RectangleShape { ... special case rectangle syntactic sugar that makes it a square ... }
public class RectangleShape : Shape { ... rectangle properties }
public class CicleShape : Shape { ... cicle properties }
and you might even some day add
public class CircleShape : EllipseShape { ... circle special case of ellipse properties ... }
public class EllipseShape : Shape { ... ellipse properties ... }
Perhaps a different answer than you were thinking but you said Any suggestion and this will probably serve you well.