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Self Hosting ASP.NET Web API and Understanding the Routing Conventions

imageIn this post, we’ll have a quick look at ASP.NET Web API Self Hosting and Routing Conventions. ASP.NET Web APIs allow you to easily build RESTful applications on top of the .NET framework. ASP.NET Web API is bundled with ASP.NET MVC 4, but you can also self host Web APIs in your custom .NET application (like a console application or a Windows Forms application or in ASP.NET Web Forms applications).

Let us quickly build a Pet Store API to query pets using ASP.NET Web API, and we’ll be self hosting the same.

Self Hosting

Fire up Visual Studio in Admin mode, and create a new Console application. Then, install the Nuget package AspNetWebApi.SelfHost

Install-Package AspNetWebApi.SelfHost

This will add the required dependencies to your Self host application.

class Program
    {
        static void Main(string[] args)
        {

            //Create a host configuration
            var selfHostConfiguraiton = new HttpSelfHostConfiguration("http://localhost:8080");

            //Setup the routes
            selfHostConfiguraiton.Routes.MapHttpRoute(
                name: "DefaultApiRoute",
                routeTemplate: "api/{controller}/{id}",
                defaults:new { controller = "Pet", id = RouteParameter.Optional }
                );
           
            //Create Server & Wait for new connections
            using (var server = new HttpSelfHostServer(selfHostConfiguraiton))
            {
                server.OpenAsync().Wait();
                Console.WriteLine("Now Hosting at http://localhost:8080/api/{controller}");
                Console.ReadLine();
            }

        }
    }

Adding Controllers

Now, you can add your controllers by inheriting them from the ApiController base class, and the requests will be dispatched to the correct controller based on the routing information we added. So, let us have a PetController class, where you expose few pets.

  

    //-- Actual controller 

    public class PetController : ApiController
    {
        //GET All Pets /api/pet
        public IEnumerable<Pet> Get()
        {
            var rep = new PetRepository();
            return rep.GetAllPets();
        }

        //GET One Pet /api/pet/2
        public Pet Get(int id)
        {
            var rep = new PetRepository();
            return rep.GetAllPets().First(p => p.Id == id);
        }
       
    }

   //-- View Model

   public class Pet
    {
        public string Name { get; set; }
        public string Type { get; set; }
        public int Id { get; set; }
    }


    //-- Simple repository elsewhere for some mock data

    public class PetRepository
    {
        public IEnumerable<Pet> GetAllPets()
        {
            //Ideally get the data from a source
            return new List<Pet>
                    {
                        new Pet(){Name="Jim", Type="Dog", Id=1},
                        new Pet(){Name="Meow", Type="Cat",Id=2},
                        new Pet(){Name="Jam", Type="Dog",Id=3},
                        new Pet(){Name="Tommy", Type="Dog",Id=4},
                        new Pet(){Name="Bigpaw", Type="Cat",Id=5}
                    };
        }

    }

At this point, if you go to the target URL, you’ll find the XML response. Here is a formatted view. Have a look at the URL.

 

image

And for accessing one pet, you can provide the Id, which gets mapped to the Get method in controller that accepts Id parameter.

image

Default Routing Conventions

ASP.NET Web API will try to match the URL with the mapped HTTP routes. Based on the above example you can see that URLs like /api/pet or /api/pet/2 etc  are matching the route template we provided – /api/{controller}/{id}

Now, let us see how the Web API resolves the Controller and the correct action. The controller class will be picked by using the value of the {controller} variable in the URL that corresponds to the routing template.  To choose the action, the Http Action bill be used.  For example, if this is a HTTP GET request, according to the convention, that will be mapped to a method with the name starting with ‘Get’ in the controller.

As an exercise, change the first Get method’s name to a different one to GetAll, and change the name of our second Get method to GetById – and notice that above URLs are still correctly getting mapped. This convention works out of the box for the GET, POST, PUT and Delete HTTP Methods .  Instead of following the Naming conventions, you can use the attributes HttpGet, HttpPut, HttpPost and HttpDelete. For example, instead of starting the method names with ‘Get’ as in the above example, you could use the HttpGet attribute as below.

 public class PetController : ApiController
    {
        //GET All Pets /api/pet
        [HttpGet]
        public IEnumerable<Pet> FindAll()
        {
            var rep = new PetRepository();
            return rep.GetAllPets();
        }

        //GET One Pet /api/pet/2
        [HttpGet]
        public Pet FindById(int id)
        {
            var rep = new PetRepository();
            return rep.GetAllPets().First(p => p.Id == id);
        }
       
    }

You might be wondering why the default mapping scheme is limited to the GET, POST, PUT and DELETE actions, but this mapping scheme fits well for RESTful services. Because in REST, all URIs should identify a resource and not actions. Note that this is different than the ASP.NET MVC mapping scheme, where you can specify actions directly. How ever, you can enforce MVC style route selection by specifying the action in the route template, like

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

 

And this will enable you to choose actions by name in the URL. For example, now you can access the actions in our PetController using the URLs /api/pet/findall and /api/pet/findbyid/2   - Note that we are using the action name in the URL scheme, much like in MVC. This may be useful if you want to build RPC/HTTP APIs.

While this is a quick introduction, you may refer more detailed tutorials on these topics at http://www.asp.net/web-api/overview

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