I my application, I use a table per concrete class hierarchy strategy.
I didn't introduce a discriminant column into my tables as this information is useless for Hibernate with this mapping.

My mapping file looks like:

<hibernate-mapping>

<!--
Mapping for Super class
-->
<class name="SuperClass" abstract="true">
<id name="objectId" type="string" unsaved-value="null">
<column name="OBJECT_ID" sql-type="char(32)" not-null="true"/>
<generator class="uuid.hex"/>
</id>

<version name="versionNumber" column="VERSION_NUMBER"/>
......

<union-subclass name="SubClassA" table="SUBCLASS_A">
<property name="businessId" column="BUSINESS_ID" not-null="true"/>
.......
</union-subclass>

<union-subclass name="SubClassB" table="SUBCLASS_B">
<property name="businessId" column="BUSINESS_ID" not-null="true"/>
.......
</union-subclass>
.....
</class>
</hibernate-mapping>

Then, I want to build a polymorphic HQL request using the 'class' property, an error is raised.
The request is "select obj.class from SuperClass obj"

So, the question is: Must I add a discriminator column if I want to use the class property even is this information is useless for Hibernate ?

Thanks a lot in advance for any help.
(Note I use hibernate version 3.1.3)