[aspnetcore] Improve model inheritance support by including JsonSubTypes to properly handle serialization (#8384)

* Add JsonSubTypes to templates

* Add JsonSubTypes to templates

Co-authored-by: Anders Gilje <agilje@slb.com>

Author: goexplore

modules/openapi-generator/src/main/resources/aspnetcore/3.0/Project.csproj.mustache

@@ -40,6 +40,7 @@
     <PackageReference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" Version="{{newtonsoftVersion}}" />
 {{/useNewtonsoft}}
 {{/useSwashbuckle}}
+    <PackageReference Include="JsonSubTypes" Version="1.8.0" />
   </ItemGroup>
   <ItemGroup>
     <!--<DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="{{aspnetCoreVersion}}.0" />-->

modules/openapi-generator/src/main/resources/aspnetcore/3.0/model.mustache

@@ -7,6 +7,13 @@ using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
 using System.Runtime.Serialization;
 using Newtonsoft.Json;
+{{#models}}
+{{#model}}
+{{#discriminator}}
+using JsonSubTypes;
+{{/discriminator}}
+{{/model}}
+{{/models}}
 using {{packageName}}.Converters;
 
 {{#models}}
@@ -17,6 +24,12 @@ namespace {{modelPackage}}
     /// {{description}}
     /// </summary>
     [DataContract]
+    {{#discriminator}}
+    [JsonConverter(typeof(JsonSubtypes), "{{{discriminatorName}}}")]
+    {{#mappedModels}}
+    [JsonSubtypes.KnownSubType(typeof({{{modelName}}}), "{{^vendorExtensions.x-discriminator-value}}{{{mappingName}}}{{/vendorExtensions.x-discriminator-value}}{{#vendorExtensions.x-discriminator-value}}{{{.}}}{{/vendorExtensions.x-discriminator-value}}")]
+    {{/mappedModels}}
+    {{/discriminator}}
     public {{#modelClassModifier}}{{modelClassModifier}} {{/modelClassModifier}}class {{classname}} : {{#parent}}{{{parent}}}, {{/parent}}IEquatable<{{classname}}>
     {
         {{#vars}}