Creating a Web API service with F# and hosting it on Azure

In this post I want to look at how to create a Web API project with F# and host it on Azure. This will part of a blog series on how to create a mobile application (incl. the backend) based on F#. The blog post assumes that you the reader has a basic understanding of how to create a Web API web service.

F# is a functional programming language based on the .Net Framework which contrary to many other functional programming languages also makes it a general purpose language. In my endeavor to explore a functional programming language I chose F# as it will allow me to create not only .Net applications but also Xamarin based cross platform apps.

To deploy to Azure you will need a valid Azure account. Alternatively you can run the App on your local machine.

Setting up the project

I’ll be using Visual Studio 2015 RC for this setup but you can follow along on VS 2013 just as well. Create a new project then go to Online projects, Select Visual F# and then select F# MVC 5. This only has to be done during the first setup. From now on you will find the project template under the Installedproject templates.

Having a look at the solution

If you are familiar with a Web API solution you will find yourself right at home.

Under Controllers you find the expected definitions, as well as under models. The Global.asax.fs also has a familiar ring to it:

namespace FSharpWebSample

open System
open System.Net.Http
open System.Web
open System.Web.Http
open System.Web.Routing

type HttpRoute = {
    controller : string
    id : RouteParameter }

type Global() =
    inherit System.Web.HttpApplication() 

    static member RegisterWebApi(config: HttpConfiguration) =
        // Configure routing
        config.MapHttpAttributeRoutes()
        config.Routes.MapHttpRoute(
            "DefaultApi", // Route name
            "api/{controller}/{id}", // URL with parameters
            { controller = "{controller}"; id = RouteParameter.Optional } // Parameter defaults
        ) |> ignore

        // Configure serialization
        config.Formatters.XmlFormatter.UseXmlSerializer <- true
        config.Formatters.JsonFormatter.SerializerSettings.ContractResolver <- Newtonsoft.Json.Serialization.CamelCasePropertyNamesContractResolver()

        // Additional Web API settings

    member x.Application_Start() =
        GlobalConfiguration.Configure(Action<_> Global.RegisterWebApi)

Extending the Controller

When we look at the controller we see that an array of the model is created and there is on method that will return the list. Let’s extend the controller to return a value requested by it’s Id. So first we have to extend the model Car.fs:

namespace FSharpWebSample.Models

open Newtonsoft.Json

[<CLIMutable>]
type Car = {
    Make : string
    Model : string
    Id : int
}

Now we can extend the CarsController.fs so that we can filter the list and get the according value:

namespace FSharpWebSample.Controllers
open System
open System.Collections.Generic
open System.Linq
open System.Net.Http
open System.Web.Http
open FSharpWebSample.Models

/// Retrieves values.
type CarsController() =
    inherit ApiController()
    
    let values = [ { Make = "Ford"; Model = "Mustang"; Id = 1 }; { Make = "Nissan"; Model = "Titan"; Id = 2 }; { Make = "Audi"; Model = "R8"; Id = 3 } ]
    
    /// Gets all values.
    member x.Get() = values
    
    member x.Get(id:int) = values |> List.filter(fun v -> v.Id = id)

Deploying to Azure

Deploying to azure luckily is luckely the same as it always has been for C#, right click onto the Web API project, select Publish…, Microsoft Azure Web Apps then create a new web app enter a name and finally click on Pubish. Now all that is left is to test the web service so lets do this the manual way.

Testing the controller

Opening the prefered browser of your choice e.g. the new Edge browser enter the path to the azure website and be executing the following URI:

http://fsharpwebsample.azurewebsites.net/api/cars

We receive the entire list:

[{"make":"Ford","model":"Mustang","id":1},{"make":"Nissan","model":"Titan","id":2},{"make":"Audi","model":"R8","id":3}]

When we add a Id parameter:

http://fsharpwebsample.azurewebsites.net/api/cars/3

We only receive the requested record:

[{"make":"Audi","model":"R8","id":3}]

Conclusion

Creating a Web API service with F# is not much different than creating it with C# thanks to Ryan Riley and Daniel Mohl who provide the F# MVC 5 template. Also uploading it to Azure and sending requests are the way one would expect the service to run. Looking forward to go on further down the F# rabbit hole.

You can find the sample on GitHub.