Migrating from WCF Web API to ASP.NET Web API by Mark Seemann

Now that the WCF Web API has ‘become' the ASP.NET Web API, I've had to migrate a semi-complex code base from the old to the new framework. These are my notes from that process.

Migrating Project References #

As far as I can tell, the ASP.NET Web API isn't just a port of the WCF Web API. At a cursory glance, it looks like a complete reimplementation. If it's a port of the old code, it's at least a rather radical one. The assemblies have completely different names, and so on.

Both old and new project, however, are based on NuGet packages, so it wasn't particularly hard to change.

To remove the old project references, I ran this NuGet command:

Uninstall-Package webapi.all -RemoveDependencies

followed by

Install-Package aspnetwebapi

to install the project references for the ASP.NET Web API.

Rename Resources to Controllers #

In the WCF Web API, there was no naming convention for the various resource classes. In the quickstarts, they were sometimes called Apis (like ContactsApi), and I called mine Resources (like CatalogResource). Whatever your naming convention was, the easiest things is to find them all and rename them to end with Controller (e.g. CatalogController).

AFAICT you can change the naming convention, but I didn't care enough to do so.

Derive Controllers from ApiController #

Unless you care to manually implement IHttpController, each Controller should derive from ApiController:

public class CatalogController : ApiController

Remove Attributes #

The WCF Web API uses the [WebGet] and [WebInvoke] attributes. The ASP.NET Web API, on the other hand, uses routes, so I removed all the attributes, including their UriTemplates:

//[WebGet(UriTemplate = "/")]
public Catalog GetRoot()

Add Routes #

As a replacement for attributes and UriTemplates, I added HTTP routes:

routes.MapHttpRoute(
    name: "DefaultApi",
    routeTemplate: "{controller}/{id}",
    defaults: new { controller = "Catalog", id = RouteParameter.Optional }
);

The MapHttpRoute method is an extension method defined in the System.Web.Http namespace, so I had to add a using directive for it.

Composition #

Wiring up Controllers with Constructor Injection turned out to be rather painful. For a starting point, I used Nikos Baxevanis' guide, but it turns out there are further subtleties which should be addressed (more about this later, but to prevent a stream of comments about the DependencyResolver API: yes, I know about that, but it's inadequate for a number of reasons).

Media Types #

In the ASP.NET Web API application/json is now the default media type format if the client doesn't supply any Accept header. For the WCF Web API I had to resort to a hack to change the default, so this was a pleasant surprise.

It's still pretty easy to add more supported media types:

GlobalConfiguration.Configuration.Formatters.XmlFormatter
    .SupportedMediaTypes.Add(
        new MediaTypeHeaderValue("application/vnd.247e.artist+xml"));
GlobalConfiguration.Configuration.Formatters.JsonFormatter
    .SupportedMediaTypes.Add(
        new MediaTypeHeaderValue("application/vnd.247e.artist+json"));

(Talk about a Law of Demeter violation, BTW...)

However, due to an over-reliance on global state, it's not so easy to figure out how one would go about mapping certain media types to only a single Controller. This was much easier in the WCF Web API because it was possible to assign a separate configuration instance to each Controller/Api/Resource/Service/Whatever... This, I've still to figure out how to do...

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