ElementCollection geting ConcurrentModificationException

uebi_belli · **Joined:** Mon Jul 20, 2009 3:48 pm **Posts:** 3

Hello,

I have mongodb database Collection an array of objects with another array of objects:

Code:

@Entity
public class Tournament {
    @Id
    Long id;

    @ElementCollection
    @CollectionTable
    private List<Edition>;
}

@Embeddable
public class Edition {

    @ElementCollection
    @CollectionTable
    private List<Round>
}

@Embeddable
public class Round {

    blabla;
}

When hibernate starts I get the follow error:

Code:

Caused by: java.util.ConcurrentModificationException
   at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) [rt.jar:1.8.0_31]
   at java.util.ArrayList$Itr.remove(ArrayList.java:865) [rt.jar:1.8.0_31]
   at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1698) [hibernate-core-4.3.7.Final.jar:4.3.7.Final]
   at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1426) [hibernate-core-4.3.7.Final.jar:4.3.7.Final]
   at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1846) [hibernate-core-4.3.7.Final.jar:4.3.7.Final]
   at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:852) [hibernate-entitymanager-4.3.7.Final.jar:4.3.7.Final]
   at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:845) [hibernate-entitymanager-4.3.7.Final.jar:4.3.7.Final]
   at org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl.withTccl(ClassLoaderServiceImpl.java:398) [hibernate-core-4.3.7.Final.jar:4.3.7.Final]
   at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:844) [hibernate-entitymanager-4.3.7.Final.jar:4.3.7.Final]
   at org.hibernate.jpa.HibernatePersistenceProvider.createContainerEntityManagerFactory(HibernatePersistenceProvider.java:152) [hibernate-entitymanager-4.3.7.Final.jar:4.3.7.Final]
   at org.hibernate.ogm.jpa.HibernateOgmPersistence.createContainerEntityManagerFactory(HibernateOgmPersistence.java:105) [hibernate-ogm-core-4.1.1.Final.jar:4.1.1.Final]
   at org.jboss.as.jpa.service.PersistenceUnitServiceImpl.createContainerEntityManagerFactory(PersistenceUnitServiceImpl.java:318) [wildfly-jpa-8.2.0.Final.jar:8.2.0.Final]
   at org.jboss.as.jpa.service.PersistenceUnitServiceImpl.access$1100(PersistenceUnitServiceImpl.java:67) [wildfly-jpa-8.2.0.Final.jar:8.2.0.Final]
   at org.jboss.as.jpa.service.PersistenceUnitServiceImpl$1$1.run(PersistenceUnitServiceImpl.java:167) [wildfly-jpa-8.2.0.Final.jar:8.2.0.Final]

Any help will be welcome =)

Gunnar · **Joined:** Sat Jan 24, 2009 12:46 pm **Posts:** 388

Hi,

Such a mapping violates the JPA spec, an embeddable which is contained in an element collection must not contain another element collection itself.

But I think you already knew that, given that your example exactly matches the one from this SO post which discusses that mapping: http://stackoverflow.com/questions/22126397/embeddable-and-elementcollection-nesting ;)

That being said, we theoretically could support such mapping for document stores such as MongoDB where we can store everything as nested structures within one JSON document. But as this is a limitation within the ORM engine itself, I believe chances for this are rather low.

--Gunnar

emmanuel · **Posted:** Fri Mar 20, 2015 4:06 am

Yes I guess it's because the relational model would be really strange and involve a lot of duplications. Plus I think we could never support the bags of bags semantic as we could not differentiate duplication from one level to duplication from the other level.

If we limit our mapping to Sets, Maps or indexed Lists (@OrderColumn), then I believe it is theoretically possible. In which case, as you say Gunnar, we could make it work for document stores. We would need to improve ORM itself to detect this and offer a pluggable strategy (fail or continue). And then use a continue approach to implement it in OGM.

I think it is more practical to instead pursue the following:

1. map Edition as a plain entity and use @OnetoMany(cascade=CascadeType.ALL, orphanRemoval=true): this simulates @ElementCollection semantic
2. offer on OGM the ability to embed a (collection of) associated entity within another int he targeted structure to do one lookup for the whole structure.

Step 1. should satisfy you already for the time being.

uebi_belli · **Joined:** Mon Jul 20, 2009 3:48 pm **Posts:** 3

Would be very good if JPA had a way to say: "Hey, it's a nosql database and the game rules will be different" =)

Emmanuel:
To map Edition as a @Entity I need to create it physically in the database, right?

To solve this problem I had to create another Collection in my database to store my sublists and we know that it makes the database lose some performance with joins and make my work a bit harder =)

emmanuel · **Posted:** Mon Mar 23, 2015 8:57 am

Not really harder on your side as OGM does the work for you but yes it would add a second collection.