Hi, i'm evaluating Hibernate to provide an O/R mapping onto a legacy database.
I followed the examples provided in section 7.5.1 of Hibernate 3.1.x documentation: "Bidirectional associations with join tables". The one-to-one example, with Person and Adddress connected by a bidirectional association mapped on a join table (PersonAddress), works fine. The same for the many-to-one association mapped on a join table.

The problem starts by simply adding a subclass to Address, using the <joined-subclass> strategy. When you call Configuration.buildSessionFactory, an exception is thrown during the evaluation of the added subclass



Any idea on what causes this behaviour ?

Could you post your mapping documents?

test/Address.hbm.xml:


test/Person.hbm.xml


test/Worker.hbm.xml


I've found two ways for removing the exception I posted above:
- Remove Worker from the hibernate configuration (i.e. returning to a non-hierarchical model, with 2 classes and their join association)
- Remove the <join> association from Address and Person (i.e. preserving the hierarchical model, with 3 classes, but removing the join association)
In other words I can't make <join> and <joined-sublcass> to co-exist.

Btw, I've found this workaround for mapping my legacy one-to-one and many-to-one associations on join tables in case of hierarchies of joined subclasses:
- Build the Java classes and mapping files as if the associations are MANY-TO-MANY (see section 7.5.3 of Hibernate 3.1.x manual)


- Adds to the Java classes, but NOT to the mapping files, a pair of suitable setter and getter, implemented using the above many-to-many setter and getter, enforcing the "one" max cardinality.


In this way the class exposes one-to-one methods, Hibernate does the job of updating the underlying join table, and the getter/setter methods enforces programmatically the cardinality. And all works with hierarchies of classes and with one-to-one or many-to-one associations put at any level of the hierarchy.

From the Hibernate documentation, it looks like the <join> element is not used to do bidirectional relationships with a join table, but to allow properties of a single class to be split among multiple tables. In this case, your problem is that the <join> in Address and <join> in Person are both using the same table for these split properties.

According to section 7.5.1 and section 7.5.2 of the Hibernate 3.1.x manual, the <join> element can be used to map as well bidirectional associations. And it works perfectly. Until you introduce a joined subclass in the system.

Well, I finally got around to actually trying this out. Want to hear something funny? The bug has nothing to do with trying to get a many-to-many relationship working with <join>. Here's my mapping:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping default-access="field" package="com.david.model">
<class name="Person" table="person" select-before-update="true" dynamic-update="true">
<id name="id" column="id" type="long">
<generator class="native"/>
</id>
<version name="version" column="version" type="long"/>
<property name="birthDate" column="birth_date" type="date"/>
<property name="firstName" column="first_name" type="string" length="20" not-null="true"/>
<property name="lastName" column="last_name" type="string" length="20" not-null="true"/>
<join table="personDesc" inverse="false" optional="true">
<key column="personId"/>
<property name="hairColor" column="hair_color" type="string" length="10"/>
</join>
</class>
<joined-subclass name="Employee" table="employee" extends="Person">
<key column="personId"/>
<property name="salary" column="salary" type="big_decimal"/>
</joined-subclass>
</hibernate-mapping>

What I am doing is splitting the properties for the base Person - most go in the person table, but the hair color is in the personDesc table. I get the same exception when Hibernate tries to create the session factory - for Employee, it can't find the personDesc table. After a quick run under debug, it turns out that JoinedSubclassEntityPersister examines all properties of the base class and subclass, but expects that all properties (at least, based on the above mapping) are in the person or employee table, and freaks out when it sees that hairColor belongs to the personDesc table.

Looks like you found a real Hibernate bug!

Ok, keeminor found a bug, DWright confirmed the existence... I'm having the exact same problem... should I use the work around suggested by keeminor or is there any patch I could use?

Thanks a lot for your help :-)