Global route prefix in ASP.NET Core 2.0

MvcOptionsExtensions.cs

using System.Linq;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.ApplicationModels;
using Microsoft.AspNetCore.Mvc.Routing;

namespace MyWebApi.Extensions
{
    public static class MvcOptionsExtensions
    {
        public static void UseGeneralRoutePrefix(this MvcOptions opts, IRouteTemplateProvider routeAttribute)
        {
            opts.Conventions.Add(new RoutePrefixConvention(routeAttribute));
        }

        public static void UseGeneralRoutePrefix(this MvcOptions opts, string prefix)
        {
            opts.UseGeneralRoutePrefix(new RouteAttribute(prefix));
        }
    }
    
    public class RoutePrefixConvention : IApplicationModelConvention
    {
        private readonly AttributeRouteModel _routePrefix;

        public RoutePrefixConvention(IRouteTemplateProvider route)
        {
            _routePrefix = new AttributeRouteModel(route);
        }

        public void Apply(ApplicationModel application)
        {
            foreach (var selector in application.Controllers.SelectMany(c => c.Selectors))
            {
                if (selector.AttributeRouteModel != null)
                {
                    selector.AttributeRouteModel = AttributeRouteModel.CombineAttributeRouteModel(_routePrefix, selector.AttributeRouteModel);
                }
                else
                {
                    selector.AttributeRouteModel = _routePrefix;
                }   
            }
        }
    }
}

Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using MyWebApi.Extensions;

namespace MyWebApi
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc(o => { o.UseGeneralRoutePrefix("api/v{version:apiVersion}"); });
            services.AddApiVersioning(o => o.ReportApiVersions = true);
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseMvc();
        }
    }
}

TestController.cs

using Microsoft.AspNetCore.Mvc;

namespace MyWebApi.Controllers
{
    [ApiVersion("1")]
    [ApiVersion("2")]
    [Route("test")]
    public class TestController : Controller
    {
        [HttpGet("version"), MapToApiVersion("1")]
        public IActionResult GetV1()
        {
            return new OkObjectResult("Version One");
        }
        [HttpGet("version"), MapToApiVersion("2")]
        public IActionResult GetV2()
        {
            return new OkObjectResult("Version Two");
        }
    }
}

Thanks, that was great help for me. Using a similar method I wrote an adapter to support [RoutePrefix] and ease a migration from an old WebAPI project to ASP.NET Core.