<class name="MainTable" table="MAIN_TABLE" mutable="false">
<id name="Id" column="rvcplc" type="int" length="10">
  <generator class="assigned"/>
</id>
<bag name="JoinedRecords" table="JOIN_TABLE" order-by="main_table_id">
  <key column="main_table_id" not-null="true"/>
  <composite-element class="JoinTable">
    <parent name="parentRecord"/>
    <many-to-one name="ThirdTable" column="third_table_id"/>
  </composite-element>
</bag>

@Entity()
@Table(name="MAIN_TABLE")
@Immutable
public class MainTable extends BusinessEntity implements IMainTable
{
   @Id
   @Type(type = "LongToNull")
   @Column(name = "id")
   private long id;

   @ElementCollection
   @CollectionTable(name="JOIN_TABLE", joinColumns={@JoinColumn(name="main_table_id")})
   private List<IJoinTable> joinedRecords = new ArrayList<IJoinTable>();
}

@Embeddable()
@Table(name = "JOIN_TABLE")
@Immutable
public class JoinTable implements Serializable, IJoinTable
{
    @SuppressWarnings("unused")
    @Id
    private JoinTablePK pkId;

    @Parent
    @Column(name = "main_table_id")
    private IMainTable parentRecord;

    @ManyToOne(targetEntity = ThirdTable.class)
    @JoinColumn(name = "third_table_id")
    private IThirdTable thirdTable;

    public static class JoinTablePK implements Serializable
    {
          // foo
    }
}