Hi, I am fairly new to NH and have encountered an issue.

Could someone please offer me some advice?

I have 3 classes... Entity, WorkItem and InvoiceItem.
I have 2 tables... WorkItem and InvoiceItem.

WorkItem inherits from Entity and InvoiceItem Inherits from WorkItem.

I have created as abstract class Entity as all my classes will contain the properties Id and Version.

This code works fine
var test = session.CreateCriteria(typeof(WorkItem)).List<WorkItem>();

The sql generated by this code tries to map Id and Version to the InvoiceItem Table. However, it should be creating an Inner Join bewteen the InvoiceItem table and the WorkItem Table.
var test = session.CreateCriteria(typeof(InvoiceItem)).List<InvoiceItem>();


Below is my comfiguration mapping.

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
assembly="Example.Entities"
namespace="Example.Entities">
<class name="Entity" lazy="true" abstract="true" polymorphism="implicit">

<id name="Id">
<generator class="guid" />
</id>

<version name="Version" type="Example.Entities.Hibernate.UserTypeTimestamp,
Example.Entities.Hibernate" unsaved-value="null" generated="always" />

</class>
</hibernate-mapping>


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
assembly="Example.Entities"
namespace="Example.Entities">
<union-subclass name="WorkItem" extends="Entity">
<property name="Label"/>
</union-subclass>
</hibernate-mapping>


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
assembly="Example.Entities"
namespace="Example.Entities">
<joined-subclass name="InvoiceItem" extends="WorkItem">
<key column="Id"/>
<property name="Number"/>
</joined-subclass>
</hibernate-mapping>

Could this be a fundamental bug with NHibernate?

I haven't used union-join, yet, since I'm still working with 1.2. But from the documention, I would say this is correct. Union-join is a "table-per-concrete-class" strategy. That means, every subclass has its own table, which contains all columns. In my understanding there won't be any joins, just unions.

Thanks for the reply. Greatly appreciated.

Do you know if this can be achieved with NHibernate?

Any advice would be greatly appreciated.

What exactly do you want to do ? A base table with the fields from the abstract class and a second table for each subclass that only contains the subclasses fields ? Then you need this approach:

http://www.nhforge.org/doc/nh/en/index.html#inheritance-tablepersubclass-discriminator