<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
   <class name="Abcdefg.Budget, Abcdefg.Library" table="customer_budget">
      
      <id name="Id" column="budget_id" unsaved-value="0">
         <generator class="identity"/>
      </id>
      
      <property name="Year" column="budget_year"/>
      
      <joined-subclass name="Abcdefg.CustomerBudget, Abcdefg.Library" table="customer_budget">
      
         <key column="budget_id"/>
         
         
         <many-to-one name="Customer" class="Abcdefg.Customer, Abcdefg.Labels" />
      
      </joined-subclass>
      
      
      
      <joined-subclass name="Abcdefg.MiscBudget, Abcdefg.Library" table="budget_misc">
      
         <key column="budget_id"/>
         
         <property column="Practice" name="Practice" type="String"/>
         <property column="Platform" name="Platform" type="String"/>
      
      </joined-subclass>
   </class>
</hibernate-mapping>

  at NHibernate.Mapping.Subclass.CreateForeignKey()
   at NHibernate.Cfg.Binder.BindJoinedSubclass(XmlNode node, Subclass model, Mappings mappings)
   at NHibernate.Cfg.Binder.PropertiesFromXML(XmlNode node, PersistentClass model, Mappings mappings)
   at NHibernate.Cfg.Binder.BindRootClass(XmlNode node, RootClass model, Mappings mappings)
   at NHibernate.Cfg.Binder.BindRoot(XmlDocument doc, Mappings model)
   at NHibernate.Cfg.Configuration.AddValidatedDocument(XmlDocument doc)
   at NHibernate.Cfg.Configuration.AddInputStream(Stream xmlInputStream)

2005-12-29 11:07:34,185 [6056] INFO  NHibernate.Cfg.Configuration - Found mapping documents in assembly: Budget.hbm.xml
2005-12-29 11:07:34,185 [6056] INFO  NHibernate.Dialect.Dialect - Using dialect: NHibernate.Dialect.MsSql2000Dialect
2005-12-29 11:07:34,185 [6056] INFO  NHibernate.Cfg.Binder - Mapping class: Abcdefg.Budget -> customer_budget
2005-12-29 11:07:34,185 [6056] DEBUG NHibernate.Cfg.Binder - Mapped property: Id -> budget_id, type: Int32
2005-12-29 11:07:34,185 [6056] DEBUG NHibernate.Cfg.Binder - Mapped property: Year -> budget_year, type: Int32
2005-12-29 11:07:34,185 [6056] INFO  NHibernate.Cfg.Binder - Mapping joined-subclass: Abcdefg.CustomerBudget -> customer_budget
2005-12-29 11:07:34,185 [6056] ERROR NHibernate.AssertionFailure - An AssertionFailure occured - this may indicate a bug in NHibernate
NHibernate.AssertionFailure: Not a joined-subclass
2005-12-29 11:07:34,201 [6056] ERROR NHibernate.Cfg.Configuration - Could not configure datastore from input stream
NHibernate.AssertionFailure: Not a joined-subclass
   at NHibernate.Mapping.Subclass.CreateForeignKey()
   at NHibernate.Cfg.Binder.BindJoinedSubclass(XmlNode node, Subclass model, Mappings mappings)
   at NHibernate.Cfg.Binder.PropertiesFromXML(XmlNode node, PersistentClass model, Mappings mappings)
   at NHibernate.Cfg.Binder.BindRootClass(XmlNode node, RootClass model, Mappings mappings)
   at NHibernate.Cfg.Binder.BindRoot(XmlDocument doc, Mappings model)
   at NHibernate.Cfg.Configuration.AddValidatedDocument(XmlDocument doc)
   at NHibernate.Cfg.Configuration.AddInputStream(Stream xmlInputStream)

public abstract class Budget
   {
      private int m_id;

      public int Id
      {
         get { return m_id; }
         set { m_id = value; }
      }
   }

   public class CustomerBudget : Budget
   {
      private Customer m_customer;

      public Customer ParentCustomer
      {
         get { return m_customer; }
         set { m_customer = value; }
      }
   }

   public class MiscBudget : Budget
   {
      private string m_platform;
      private string m_practice;

      public string Platform
      {
         get { return m_platform; }
         set { m_platform = value; }
      }

      public string Practice
      {
         get { return m_practice; }
         set { m_practice = value; }
      }
   }