2 FETCH Joins in 1 query

[juergen.zimmermann]

I'm using JBoss 4.0.5GA with EJB3 annotations. I want to read objects of class Customer and also fetch their orders plus the shipments of these orders. I tried this named query:

SELECT DISTINCT c
FROM Customer c
 LEFT JOIN FETCH c.orders o
 LEFT JOIN FETCH o.shipments
WHERE c.lastname = :lastname

However, I get the following exception:

org.hibernate.HibernateException: cannot simultaneously fetch multiple bags
 at org.hibernate.loader.BasicLoader.postInstantiate(BasicLoader.java:66)
 at org.hibernate.loader.hql.QueryLoader.<init>(QueryLoader.java:101)
 at org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:181)
 at org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:111)
 at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:77)
 at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:56)
 at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:72)
 at org.hibernate.impl.SessionFactoryImpl.checkNamedQueries(SessionFactoryImpl.java:400)
 at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:351)
 at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1218)
 at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:688)

What's going wrong? Any hint is appreciated!

[maxandersen]

the stack trace says it all....

there is no way for hibernate to figure out the unique rows from a joined resultset with multiple bags.

Thus instead of creating duplicate entries in your llist we fail with the stacktrace.

In the future we plan to provide a fallback for this scenario where a second (sub)select will be done to load the other bags.

[juergen.zimmermann]

Hmm, the attributes Customer.orders and Order.shipments are annotated with

@OneToMany(...)
@OrderBy(...)

I thought that bags can be avoided this way.

[maxandersen]

but your Orders is a List, right ?

[juergen.zimmermann]

Yes, both "orders" and "shipments" are of type List<>.

Will adding @IndexColumn solve the problem?