I tried one-to-many mapping with Hibernate, and query the result back using either HQL or Criteria query. I found the outer-join doesn't exactly work as it should be. Could some one give me some light? that's is expected behaviro or bug?

options: HQL
outer-join="false": correct
outer-join="true": outer-join happen, but too many states(= State x city)


options: Criteria
outer-join="false": correct
outer-join="true": outer-join not happen, result is correct.




Hibernate version:
Hibernate 2.1.6

Mapping documents:
<set name="city" lazy="true" inverse="true" cascade="all" outer-join="true" >
<key column="STATE_ID"/>
<one-to-ma

Code between sessionFactory.openSession() and session.close(): use either HQL or Criteria
// Iterator iter = session.find("from State").iterator();
// while (iter.hasNext()) {
// State state = (State) iter.next();
// Iterator cities = state.getCity().iterator();
// while (cities.hasNext()) {
// City city = (City) cities.next();
// System.out.println(city.getId()+ "city" + city.getName() );
// }
// System.out.println(state.getId() + "state" + state.getName() );
// }
Criteria crit = session.createCriteria(State.class);
List states = crit.list();
System.out.println("Size: " + states.size());
for (int i=0; i< states.size(); i++) {
State state = (State) states.get(i);
Iterator cities = state.getCity().iterator();
while (cities.hasNext()) {
City city = (City) cities.next();
System.out.println(city.getId()+ "city" + city.getName() );
}
System.out.println(state.getId() + "state" + state.getName() );
}

Full stack trace of any exception that occurs:

Name and version of the database you are using:
HSQLDB

Ok, I find partial answer. HQL ignore outer-join..I have to do it explicitily if I want it.

However, I still can not find weather the outer-join return from Criteria is correct.
I guess the outer-join for one-to-many relation was never intended for group fetching(only used for fetch one entity?).

Seems this is expected behavior. Hibernate doesn't get rid of the duplication. However, it sucks a little since I have to change the code based on if I set the outer-join to be true or not.

==== Here was the answer ==
gavin
Hibernate Team

Joined: 26 Aug 2003
Posts: 3926
Location: Melbourne, Australia

Posted: Wed Sep 22, 2004 2:41 pm Post subject:

Um. It is not 33 objects, it is 33 references to the same object. Basically, there is no reason why Hibernate can do this unique-ification any more efficiently than you can do it.