Can not use joined-subclass of xml mapping to extend the mappings build with NHibernate.Mapping.ByCode

[beginor]

I am refacting the mapping of NHibernate.AspNetCore.Identity to NHibernate.Mapping.ByCode , as descripted in the issue https://github.com/nhibernate/NHibernate.AspNetCore.Identity/issues/16 .

I have rewrite the orignal xml mapping of NHibernate.AspNetCore.Identity with ClassMapping<T>, the code looks like this:

public class IdentityRoleMappingPostgreSql : ClassMapping<IdentityRole> {

    public IdentityRoleMappingPostgreSql() {
        Schema("public");
        Table("aspnet_roles");
        Id(e => e.Id, id => {
            id.Column("id");
            id.Type(NHibernateUtil.String);
            id.Length(32);
            id.Generator(Generators.TriggerIdentity);
        });
        Property(e => e.Name, prop => {
            prop.Column("name");
            prop.Type(NHibernateUtil.String);
            prop.Length(64);
            prop.NotNullable(true);
            prop.Unique(true);
        });
        /* other property mappings ignored here .*/
    }

}

The full mapping code is here:

https://github.com/nhibernate/NHibernate.AspNetCore.Identity/tree/master/src/NHibernate.AspNetCore.Identity/Entities

Then I try to extend these mappings with joined-sublcass of xml mapping, like this:

<?xml version="1.0" encoding="UTF-8" ?>
<hibernate-mapping
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  xmlns="urn:nhibernate-mapping-2.2"
  namespace="WebTest.Entities" assembly="WebTest">

  <joined-subclass name="AppRole" schema="public" table="app_roles" extends="NHibernate.AspNetCore.Identity.IdentityRole, NHibernate.AspNetCore.Identity, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
    <key column="id" />
    <property name="Description" column="description" type="string" length="256" />
  </joined-subclass>

</hibernate-mapping>

I got the following exception when setting up nhibernate:

NHibernate.MappingException : These classes referenced by 'extends' were not found:
FullName:NHibernate.AspNetCore.Identity.IdentityRole - Name:NHibernate.AspNetCore.Identity.IdentityRole, NHibernate.AspNetCore.Identity, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
FullName:NHibernate.AspNetCore.Identity.IdentityUser - Name:NHibernate.AspNetCore.Identity.IdentityUser, NHibernate.AspNetCore.Identity, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
   at NHibernate.Cfg.MappingsQueue.CheckNoUnavailableEntries()
   at NHibernate.Cfg.Configuration.SecondPassCompile()
   at NHibernate.Cfg.Configuration.BuildMappings()
   at UnitTest.IdentityTest._02_CanSetupMappingByXml()

Then I rewrite the xml mapping with JoinedSubclassMapping<AppRole> , which works , can build session factory and query without any exception.

public class AppRoleMapping : JoinedSubclassMapping<AppRole> {

    public AppRoleMapping() {
        ExplicitDeclarationsHolder
            .AddAsRootEntity(typeof(NHIdentityRole));
        Extends(typeof(NHIdentityRole));
        Schema("public");
        Table("app_roles");
        Key(k => k.Column("id"));
        Property(
            p => p.Description,
            maping => {
                maping.Column("description");
                maping.Type(NHibernateUtil.String);
                maping.Length(256);
            }
        );
    }

}

So the issue is:

• when using JoinedSubclassMapping<T> to extend the mappings build with ClassMapping<T>, it works _01_CanExtendByCodeWithByCode;
• when using joined-subclass of xml mapping to extend the mappings build with ClassMapping<T>, get an exception of NHibernate.MappingException : These classes referenced by 'extends' were not found _02_CanExtendByCodeWithXml;
• when using joined-subclass xml mapping to extend class xml mapping, it works _03_CanExtendXmlByXml;
• when using JoinedSubclassMapping<AppRole> to extend class mapping of xml, it works _04_CanExtendXmlByByCode;

The full test code is here: https://github.com/nhibernate/NHibernate.AspNetCore.Identity/blob/master/test/UnitTest/IdentityTest.cs

Maybe there something I do wrong, or some issues with nhibernate's mappings?