วิธีทำ Versioning ด้วย Accept Header ใน C# ASP.NET WebAPI

Accept Header บอก Server ว่า Client ต้องการข้อมูลในรูปแบบไหน (MIME Types) สามารถส่ง Version ผ่าน Header Parameter ได้ เช่น:

Version=1  → StudentsV1Controller
Version=2  → StudentsV2Controller

สร้าง CustomControllerSelector เพื่ออ่าน Version จาก Header Parameter

ตัวอย่าง CustomControllerSelector

using System.Linq;
using System.Net.Http;
using System.Web.Http;
using System.Web.Http.Controllers;
using System.Web.Http.Dispatcher;

namespace WebAPI.Custom
{
    public class CustomControllerSelector : DefaultHttpControllerSelector
    {
        private HttpConfiguration _config;

        public CustomControllerSelector(HttpConfiguration config) : base(config)
        {
            _config = config;
        }

        public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
        {
            var controllers = GetControllerMapping();
            var routeData = request.GetRouteData();
            var controllerName = routeData.Values["controller"].ToString();
            string versionNumber = "";

            var acceptHeader = request.Headers.Accept.Where(a => a.Parameters
                .Count(p => p.Name.ToLower() == "version") > 0);

            if (acceptHeader.Any())
            {
                versionNumber = acceptHeader.First().Parameters
                    .First(p => p.Name.ToLower() == "version").Value;
            }

            HttpControllerDescriptor controllerDescriptor;
            if (versionNumber == "1")
            {
                controllerName = string.Concat(controllerName, "V1");
            }
            else if (versionNumber == "2")
            {
                controllerName = string.Concat(controllerName, "V2");
            }

            if (controllers.TryGetValue(controllerName, out controllerDescriptor))
            {
                return controllerDescriptor;
            }
            return null;
        }
    }
}

การลงทะเบียนใน WebApiConfig.cs

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.Services.Replace(typeof(IHttpControllerSelector), new CustomControllerSelector(config));
        config.MapHttpAttributeRoutes();
        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }
}

Controller ตัวอย่าง

// StudentV1Controller
public class StudentV1Controller : ApiController
{
    List students = new List
    {
        new StudentV1 { Id = 1, Name = "Mark" },
        new StudentV1 { Id = 2, Name = "John" }
    };
    public IEnumerable Get() => students;
    public StudentV1 Get(int id) => students.FirstOrDefault(x => x.Id == id);
}

// StudentV2Controller
public class StudentV2Controller : ApiController
{
    List students = new List
    {
        new StudentV2 { Id = 1, FirstName = "Roger", LastName = "Federer" },
        new StudentV2 { Id = 2, FirstName = "Tom", LastName = "Bruce" }
    };
    public IEnumerable Get() => students;
    public StudentV2 Get(int id) => students.FirstOrDefault(x => x.Id == id);
}

ผลลัพธ์การทดสอบ: