ASP.NET Core 3 adding route prefix

Question

In Startup.cs I added api/ to the start of my route pattern.

app.UseEndpoints(endpoints =>
{
    endpoints.MapControllerRoute(
        name: "default",
        pattern: "api/{controller}/{action=Index}/{id?}");
});

But it hasn't done anything: the old URLs continue to work and the ones that start with /api return 404. This makes no sense!

How do I get my API to be served under /api?

Answer 1

Global Route Prefix in ASP.NET Core 3.0

Create a custom MvcOptionsExtensions

    public static class MvcOptionsExtensions
    {
        public static void UseCentralRoutePrefix(this MvcOptions opts, IRouteTemplateProvider routeAttribute)
        {
            opts.Conventions.Insert(0, new RouteConvention(routeAttribute));
        }
    }

    public class RouteConvention : IApplicationModelConvention
    {
        private readonly AttributeRouteModel _centralPrefix;

        public RouteConvention(IRouteTemplateProvider routeTemplateProvider)
        {
            _centralPrefix = new AttributeRouteModel(routeTemplateProvider);
        }

        public void Apply(ApplicationModel application)
        {
            foreach (var controller in application.Controllers)
            {
                var matchedSelectors = controller.Selectors.Where(x => x.AttributeRouteModel != null).ToList();
                if (matchedSelectors.Any())
                {
                    foreach (var selectorModel in matchedSelectors)
                    {
                        selectorModel.AttributeRouteModel = AttributeRouteModel.CombineAttributeRouteModel(_centralPrefix,
                            selectorModel.AttributeRouteModel);
                    }
                }

                var unmatchedSelectors = controller.Selectors.Where(x => x.AttributeRouteModel == null).ToList();
                if (unmatchedSelectors.Any())
                {
                    foreach (var selectorModel in unmatchedSelectors)
                    {
                        selectorModel.AttributeRouteModel = _centralPrefix;
                    }
                }
            }
        }
    }

Codes in Startup.cs

public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllersWithViews(opt => {
            opt.UseCentralRoutePrefix(new RouteAttribute("api"));
            ;
        });
    }

Test of result