Sync'ing java and db entity state on reverse relation ?

From:
Aeris <aeris@example.org>
Newsgroups:
comp.lang.java.databases
Date:
Mon, 21 Jul 2014 23:56:28 +0200
Message-ID:
<53cd8c8c$0$2939$426a34cc@news.free.fr>
Hello guys,

I have some trouble with Hibernate (v3.6.10).

I use the following mapping :
    @Entity
    public class Candidacy {
        @ManyToOne(optional = false)
        @ForeignKey(name = "fk_candidacy_team")
        private Team team;
    }

    @Entity
    public class Team {
        @OneToMany(mappedBy = "team")
        @OnDelete(action = OnDeleteAction.CASCADE)
        private final Collection<Candidacy> candidacies;
    }

When I want to create a new candidacy, I use the current code :
    public class CandidacyDao {
        public Candidacy apply(Team team) {
            Candidacy candidacy = new Candidacy();
            candidacy.setTeam(team);
            team.getCandidacies().add(candidacy);
            getCurrentSession().save(candidacy);
            return candidacy;
        }
    }

But this code doesn't work in all case.
This test case don't works :
    @Test
    public void testFail() {
        final Team team = this.teamDao.get(1); // team created from dbunit
        final Candidacy candidacy = this.apply(team);
        assertThat(team.getCandidacies()).hasSize(1).contains(candidacy);
        // java.lang.AssertionError: expected size:<1> but was:<2>
        // for <[Candidacy@70dc0648, Candidacy@70dc0648]>
    }
Note the duplicated candidacy on the list at the end.

After a (lot of) debug, I understand why :
    public class org.hibernate.collection.PersistentBag {
        public boolean add(Object object) {
            if ( !isOperationQueueEnabled() ) {
                write();
                return bag.add(object);
            } else {
                queueOperation( new SimpleAdd(object) );
                return true;
            }
        }

        protected boolean isOperationQueueEnabled() {
            return !initialized && isConnectedToSession() &&
                isInverseCollection();
        }
    }

So, ?? team.getCandidacies() ?? is not previously resolved (lazy-loaded)
before the ?? .add(candidacy) ??, and even this ?? .add ?? doesn't trigger the
resolution (write access) and postpone it when the ?? .getCandidacies() ??
will be really read (on ?? assert ??).
At ?? assert ?? time, the children are really resolved, so a SELECT is done in
database, fetch all the candidacies including the newly created, and realize
the real addition, leading to a duplicated one.

If I force the ?? .getCandidacies() ?? or create directly the team from the
test, all is good :
    @Test
    public void testSuccess1() {
        final Team team = this.teamDao.get(1);
        this.logger.debug("{}", team.getCandidacies()); // force the read
        final Candidacy candidacy = this.apply(team);
        assertThat(team.getCandidacies()).hasSize(1).contains(candidacy);
    }

    @Test
    public void testSuccess2() {
        final Team team = new Team();
        getCurrentSession().save(team); // native initialization
        final Candidacy candidacy = this.apply(team);
        assertThat(team.getCandidacies()).hasSize(1).contains(candidacy);
    }

If I remove the ?? .add ?? on the DAO, the behaviour is the opposite :
    ??? If lazy-loaded before the ?? .apply ??, failure at the end because the
candidacy is not in the list of the team.
    ??? If not, test success because the ?? assert ?? will trigger the
resolution, but with no ?? .add ?? this time so no duplicate and correct list
(fetch from db).

So, my question is : how I can keep in sync the database and the java entity
state in case of children and reverse relation, in any case (previously
lazy-loaded or not) ? :'(

Thanks in advance.
--
Aeris

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