Sample showing how to implement ~/entityset/key/property kind of url support in web API OData. Run and try the url http://localhost:8080/customers(42)/ID or http://localhost:8080/customers(42)/Name for a demo.

ODataProperty.cs

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Net;
using System.Net.Http;
using System.Reflection;
using System.ServiceModel;
using System.Web.Http;
using System.Web.Http.OData;
using System.Web.Http.OData.Builder;
using System.Web.Http.OData.Formatter;
using System.Web.Http.OData.Routing;
using System.Web.Http.SelfHost;
using Microsoft.Data.Edm;

namespace ODataTests
{
    class Program
    {
        static void Main(string[] args)
        {
            HttpSelfHostConfiguration config = new HttpSelfHostConfiguration("http://localhost:8080");
            config.HostNameComparisonMode = HostNameComparisonMode.Exact;

            config.Routes.MapODataRoute("default", "", GetEdmModel());
            config.Formatters.Clear();
            config.Formatters.InsertRange(0, ODataMediaTypeFormatters.Create());

            HttpSelfHostServer server = new HttpSelfHostServer(config);
            server.OpenAsync().Wait();
            Console.WriteLine("started..");
            Console.ReadKey();
        }

        private static IEdmModel GetEdmModel()
        {
            ODataConventionModelBuilder builder = new ODataConventionModelBuilder();
            builder.EntitySet<Customer>("customers");
            return builder.GetEdmModel();
        }
    }

    public class CustomersController : ODataController
    {
        [AcceptVerbs("GET", "POST", "PUT", "POST", "PATCH", "MERGE")]
        public HttpResponseMessage HandleUnmappedRequest(ODataPath odataPath)
        {
            // Handle property GET.
            if (Request.Method == HttpMethod.Get &&
                (odataPath.PathTemplate == "~/entityset/key/property" ||
                    odataPath.PathTemplate == "~/entityset/key/cast/property"))
            {
                string propertyName = (odataPath.Segments.Last() as PropertyAccessPathSegment).PropertyName;
                string key = (odataPath.Segments[1] as KeyValuePathSegment).Value;

                // replace with code to get the entity by key.
                var customer = new Customer { ID = 42 };

                // use reflection to get the property. replace with code specific to your provider.
                PropertyInfo property = customer.GetType().GetProperty(propertyName);
                object propertyValue = property.GetValue(customer);

                // use the custom CreateResponse overload.
                return Request.CreateResponse(HttpStatusCode.OK, property.PropertyType, propertyValue);
            }

            throw new HttpResponseException(HttpStatusCode.BadRequest);
        }
    }

    public static class HttpRequestMessageExtensions
    {
        private static MethodInfo _createResponse = InitCreateResponse();

        private static MethodInfo InitCreateResponse()
        {
            Expression<Func<HttpRequestMessage, HttpResponseMessage>> expr =
                (request) => request.CreateResponse<object>(HttpStatusCode.OK, default(object));
            return (expr.Body as MethodCallExpression).Method.GetGenericMethodDefinition();
        }

        // Content negotiation doesn't use the runtime type of the object. This helper method is CreateResponse overload that passes
        // the specified type to content negotiation.
        public static HttpResponseMessage CreateResponse(this HttpRequestMessage request, HttpStatusCode status, Type type, object value)
        {
            return _createResponse.MakeGenericMethod(type).Invoke(null, new[] { request, status, value }) as HttpResponseMessage;
        }
    }

    public class Customer
    {
        public int ID { get; set; }

        public string Name { get; set; }
    }
}