Hands-On RESTful Web Services with ASP.NET Core 3

Custom constraints

If default constraints don't cover all the business rules of your application, ASP.NET Core exposes all the necessary components to extend the behavior of route constraints so that you can define your own rules. It is possible to extend routing constraints by implementing the IRouteConstraint interface provided by Microsoft.AspNetCore.Routing, like so:

using System.Collections.Generic;using Microsoft.AspNetCore.Http;using Microsoft.AspNetCore.Routing;namespace SampleAPI.CustomRouting{    public class CurrencyConstraint : IRouteConstraint    {        private static readonly IList<string> _currencies =              new List<string> { "EUR", "USD", "GBP" };                public bool Match(HttpContext httpContext, IRouter route,            string routeKey, RouteValueDictionary ...