Scott Hanselman

I dig everything that Paul Betts does. He's a lovely person and a prolific coder. One of his recent joints is called Refit. It's a REST library for .NET that is inspired by Square's Retrofit library. It turns your REST API into a live interface:

public interface IGitHubApi
{
    [Get("/users/{user}")]
    Task<User> GetUser(string user);
}

That's an interface that describes a REST API that's elsewhere. Then later you just make a RestService.For<YourInterface> and you go to town.

var gitHubApi = RestService.For<IGitHubApi>("https://api.github.com");

var octocat = await gitHubApi.GetUser("octocat");

That's lovely! It is a .NET Standard 1.4 library which means you can use it darn near everywhere. Remember that .NET Standard isn't a runtime, it's a version interface - a list of methods you can use under many different ".NETs." You can use Refit on UWP, Xamarin.*, .NET "full" Frameowrk, and .NET Core, which runs basically everywhere.

Sure, you can make your own HttpClient calls, but that's a little low level and somewhat irritating. Sure, you can look for a .NET SDK for your favorite REST interface but what if it doesn't have one? It strikes a nice balance between the low-level and the high-level.

I'll give an example and use it as a tiny exercise for Refit. I have a service that hosts a realtime feed of my blood sugar, as I'm a Type 1 Diabetic. Since I have a Continuous Glucose Meter that is attached to me and sending my sugar details to a web service called Nightscout running in Azure, I figured it'd be cool to use Refit to pull my sugar info back down with .NET.

The REST API for Nightscout is simple, but doe have a lot of options, query strings, and multiple endpoints. I can start by making a simple interface for the little bits I want now, and perhaps expand the interface later to get more.

For example, if I want my sugars, I would go

https://MYWEBSITE/api/v1/entries.json?count=10

And get back some JSON data like this:

[
{
_id: "5993c4aa8d60c09b63ba1c",
sgv: 162,
date: 1502856279000,
dateString: "2017-08-16T04:04:39.000Z",
trend: 4,
direction: "Flat",
device: "share2",
type: "sgv"
},
{
_id: "5993c37d8d60c09b93ba0b",
sgv: 162,
date: 1502855979000,
dateString: "2017-08-16T03:59:39.000Z",
trend: 4,
direction: "Flat",
device: "share2",
type: "sgv"
}
]

Where "sgv" is serum glucose value, or blood sugar.

Starting with .NET Core 2.0 and the SDK that I installed from http://dot.net, I'll first make a console app from the command line and add refit like this:

C:\users\scott\desktop\refitsugars> dotnet new console
C:\users\scott\desktop\refitsugars> dotnet add package refit

Here's my little bit of code.

• I made an object shaped like each record. Added aliases for weirdly named stuff like "sgv"
• COOL SIDE NOTE: I added <LangVersion>7.1</LangVersion> to my project so I could have my public static Main entry point be async. That's new as many folks have wanted to have a "public static async void Main()" equivalent.

After that it's REALLY lovely and super easy to make a quick strongly-typed REST Client in C# for pretty much anything. I could see myself easily extending this to include the whole NightScout diabetes management API without a lot of effort.

using Newtonsoft.Json;
using Refit;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace refitsugars
{
    public interface INightScoutApi
    {
        [Get("/api/v1/entries.json?count={count}")]
        Task<List<Sugar>> GetSugars(int count);
    }

    public class Sugar
    {
        [JsonProperty(PropertyName = "_id")]
        public string id { get; set; }

        [JsonProperty(PropertyName = "sgv")]
        public int glucose { get; set; }

        [JsonProperty(PropertyName = "dateString")]
        public DateTime itemDate { get; set; }
        public int trend { get; set; }
    }

    class Program
    {
        public static async Task Main(string[] args)
        {
            var nsAPI = RestService.For<INightScoutApi>("https://MYURL.azurewebsites.net");
            var sugars = await nsAPI.GetSugars(3);
            sugars.ForEach(x => { Console.WriteLine($"{x.itemDate.ToLocalTime()} {x.glucose} mg/dl"); });
        }
    }
}

And here's the result of the run.

PS C:\Users\scott\Desktop\refitsugars> dotnet run
8/15/2017 10:29:39 PM 110 mg/dl
8/15/2017 10:24:39 PM 108 mg/dl
8/15/2017 10:19:40 PM 109 mg/dl

You should definitely check out Refit. It's very easy and quite fun. The fact that it targets .NET Standard 1.4 means you can use it in nearly all your .NET projects, and it already has creative people thinking of cool ideas.

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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