Improve Explorer API Version From Path in Web API

src/Microsoft.AspNet.WebApi.Versioning.ApiExplorer/Description/ApiVersionParameterDescriptionContext.cs

@@ -1,5 +1,6 @@
 namespace Microsoft.Web.Http.Description
 {
+    using Microsoft.Web.Http.Routing;
     using Microsoft.Web.Http.Versioning;
     using System;
     using System.Collections.Generic;
@@ -146,7 +147,17 @@ protected virtual void AddHeader( string name )
         /// </summary>
         protected virtual void UpdateUrlSegment()
         {
-            var parameter = ApiDescription.ParameterDescriptions.FirstOrDefault( p => p.Source == FromUri && p.ParameterDescriptor == null );
+            // use the route constraints to determine the user-defined name of the route parameter; expect and support only one
+            var constraints = ApiDescription.Route.Constraints;
+            var routeParameterName = constraints.Where( p => p.Value is ApiVersionRouteConstraint ).Select( p => p.Key ).FirstOrDefault();
+
+            if ( string.IsNullOrEmpty( routeParameterName ) )
+            {
+                return;
+            }
+
+            // find and update the parameter description for the api version route parameter
+            var parameter = ApiDescription.ParameterDescriptions.FirstOrDefault( p => routeParameterName.Equals( p.Name, OrdinalIgnoreCase ) );
 
             if ( parameter == null )
             {
@@ -161,6 +172,7 @@ protected virtual void UpdateUrlSegment()
                 Configuration = action.Configuration,
                 ActionDescriptor = action,
             };
+
             RemoveAllParametersExcept( parameter );
         }
 
@@ -208,7 +220,7 @@ ApiParameterDescription NewApiVersionParameter( string name, ApiParameterSource
 
         void RemoveAllParametersExcept( ApiParameterDescription parameter )
         {
-            // note: in a scenario where multiple api version parameters are allowed, we can remove all other parameters because
+            // in a scenario where multiple api version parameters are allowed, we can remove all other parameters because
             // the api version must be specified in the path. this will avoid unwanted, duplicate api version parameters
             var collections = new ICollection<ApiParameterDescription>[] { ApiDescription.ParameterDescriptions, parameters };
 

test/Microsoft.AspNet.WebApi.Versioning.ApiExplorer.Tests/Description/ApiVersionParameterDescriptionContextTest.cs

@@ -1,6 +1,7 @@
 namespace Microsoft.Web.Http.Description
 {
     using FluentAssertions;
+    using Microsoft.Web.Http.Routing;
     using Microsoft.Web.Http.Versioning;
     using Moq;
     using System.Collections.ObjectModel;
@@ -11,6 +12,7 @@
     using System.Web.Http.Controllers;
     using System.Web.Http.Description;
     using System.Web.Http.Filters;
+    using System.Web.Http.Routing;
     using Xunit;
     using static Microsoft.Web.Http.Versioning.ApiVersionParameterLocation;
     using static System.Web.Http.Description.ApiParameterSource;
@@ -93,7 +95,12 @@ public void add_parameter_should_add_descriptor_for_path()
             // arrange
             var configuration = new HttpConfiguration();
             var action = NewActionDescriptor();
-            var description = new ApiDescription() { ActionDescriptor = action };
+            var route = new HttpRoute() { Constraints = { ["api-version"] = new ApiVersionRouteConstraint() } };
+            var description = new ApiDescription()
+            {
+                ActionDescriptor = action,
+                Route = route,
+            };
             var version = new ApiVersion( 1, 0 );
             var options = new ApiExplorerOptions( configuration );
             var context = new ApiVersionParameterDescriptionContext( description, version, options );
@@ -129,7 +136,12 @@ public void add_parameter_should_remove_other_descriptors_after_path_parameter_i
             // arrange
             var configuration = new HttpConfiguration();
             var action = NewActionDescriptor();
-            var description = new ApiDescription() { ActionDescriptor = action };
+            var route = new HttpRoute() { Constraints = { ["api-version"] = new ApiVersionRouteConstraint() } };
+            var description = new ApiDescription()
+            {
+                ActionDescriptor = action,
+                Route = route,
+            };
             var version = new ApiVersion( 1, 0 );
             var options = new ApiExplorerOptions( configuration );
             var context = new ApiVersionParameterDescriptionContext( description, version, options );
@@ -151,7 +163,12 @@ public void add_parameter_should_not_add_query_parameter_after_path_parameter_ha
             // arrange
             var configuration = new HttpConfiguration();
             var action = NewActionDescriptor();
-            var description = new ApiDescription() { ActionDescriptor = action };
+            var route = new HttpRoute() { Constraints = { ["api-version"] = new ApiVersionRouteConstraint() } };
+            var description = new ApiDescription()
+            {
+                ActionDescriptor = action,
+                Route = route,
+            };
             var version = new ApiVersion( 1, 0 );
             var options = new ApiExplorerOptions( configuration );
             var context = new ApiVersionParameterDescriptionContext( description, version, options );