jpa criteria query fails after MapJoin

Question

I have the following @Entities

@Entity public class Configuration{ @OneToMany protected Map<String, Component> components; }

and

@Entity public class Component{ protected String displayName; }

I do not understand why this works, returning all Configurations

 CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Configuration> cq = cb.createQuery(Configuration.class); Root<Configuration> pc = cq.from(Configuration.class); cq.select(pc);

But if I do a MapJoin, even without setting any conditions, it does not return anything

 CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Configuration> cq = cb.createQuery(Configuration.class); Root<Configuration> pc = cq.from(Configuration.class); MapJoin<Configuration, String, Component> mapJoin = pc.join(Configuration_.components); cq.select(pc);

What am I missing? I'm at a loss, I've been through the tutorials, but have not found the answers I need. Any help much appreciated.

JB Nizet · Accepted Answer · 2012-02-05 17:18:26Z

Because the join type is inner by default, which means that for a configuration to be returned it has to at least have one component. If none of your configurations have a component, nothing is returned.

The first query is equivalent to

select configuration.* from configuration

And the second one is equivalent to

select configuration.* from configuration inner join component on component.id = configuration.id

Collectives™ on Stack Overflow

jpa criteria query fails after MapJoin

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related