Hibernate Table per Hierarchy How to

Question

I would like to use hibernate to contain a hierarchy of objects, however the discriminator column is a foreign key to another table that contains the CODE defining the subclass type.

Is it possible to specify the code from the joined table as the discriminator, or do I have to use the key values and hope the keys stay consistent?

e.g. discriminator="square|circle" v.s. discriminator="0|1"

table: shape

area=25   shape_type_fk=0
area=10   shape_type_fk=1

table: shape_types

ID CODE
0  square
1  circle

Answer 1

Looks like you need to use joined-subclass instead of subclass. Details are here.

Answer 2

A quick test shows that you could do this:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"&gt;
<hibernate-mapping default-access="field">

  <class name="Shape" abstract="true">
    <id name="id"/>
    <discriminator formula="select CODE from SHAPE_TYPES st where st.ID=SHAPE_TYPE"/>
    <version name="version"/>

    <subclass name="Square" discriminator-value="square"/>
    <subclass name="Circle" discriminator-value="circle"/>

  </class>
</hibernate-mapping>

Now this mapping will not create the SHARE_TYPE table that is referenced in the formula Nor does it add the SHAPE_TYPE column to the SHAPE table. This you could do in the import.sql file that Hibernate reads automatically from the classpath or by mapping another class to this table.