Hibernate EntityManager doesn't throw EntityExistsException on persist

Question

I have a problem with Hibernate EntityManager.

Here is my DAO function:

public Boolean create(T element)
{
    System.out.println("To persist: "+element);
    System.out.println("PersistanceHolder: "+holder);
    System.out.println("EntityManager: "+entityManager);
    System.out.println("CRUDDao: "+this);
    System.out.println("Thread: "+Thread.currentThread());

    entityManager.getTransaction().begin();

    try
    {
        entityManager.persist(element);
    }
    catch(EntityExistsException e)
    {
        entityManager.getTransaction().rollback();
        return Boolean.FALSE;
    }

    entityManager.getTransaction().commit();

    return Boolean.TRUE;
}

My Element is this:

@Entity
public class Event {

    @Id
    String name;

    Maturity maturity;

    Integer delay;

    public Event() {
    }

    public Event(String name, Maturity maturity, Integer delay) {
        super();
        this.name = name;
        this.maturity = maturity;
        this.delay = delay;
    }

    public String getName() {
        return name;
    }
    public Maturity getMaturity() {
        return maturity;
    }
    public Integer getDelay() {
        return delay;
    }

    @Override
    public String toString() {
        return "Event [name=" + name + ", maturity=" + maturity + ", delay="
                + delay + ", toString()=" + super.toString() + "]";
    }
}

Element in the DB looks like:

Added: Event [name=Mercury, maturity=monthEnd, delay=0, toString()=bc.bacon.egg.data.local.pojos.events.Event@3b43dc25]

If I now insert a Element with a Index (Name) that already exists I get this Messages back:

To persist: Event [name=Mercury, maturity=monthEnd, delay=0, toString()=bc.bacon.egg.data.local.pojos.events.Event@7025bd08]
PersistanceHolder: bc.bacon.egg.data.local.PersistanceHolder@3d9d91bd
EntityManager: org.hibernate.jpa.internal.EntityManagerImpl@33cb2ee5
CRUDDao: bc.bacon.egg.data.local.dao.events.EventsDao@6073d6f3
Thread: Thread[qtp1055127737-17,5,main]

So a EntityExistsException is thrown and everything is fine.
But on the second run I get this:

To persist: Event [name=Mercury, maturity=monthEnd, delay=0, toString()=bc.bacon.egg.data.local.pojos.events.Event@700576a4]
PersistanceHolder: bc.bacon.egg.data.local.PersistanceHolder@3d9d91bd
EntityManager: org.hibernate.jpa.internal.EntityManagerImpl@33cb2ee5
CRUDDao: bc.bacon.egg.data.local.dao.events.EventsDao@6073d6f3
Thread: Thread[qtp1055127737-16,5,main]
Hibernate: insert into Event (delay, maturity, name) values (?, ?, ?)
Jun 18, 2015 3:10:34 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
WARN: SQL Error: 23505, SQLState: 23505
Jun 18, 2015 3:10:34 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: Eindeutiger Index oder Primärschlüssel verletzt: "PRIMARY_KEY_3 ON PUBLIC.EVENT(NAME) VALUES ('Mercury', 1)"
Unique index or primary key violation: "PRIMARY_KEY_3 ON PUBLIC.EVENT(NAME) VALUES ('Mercury', 1)"; SQL statement:
insert into Event (delay, maturity, name) values (?, ?, ?) [23505-187]
Jun 18, 2015 3:10:34 PM org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl release
INFO: HHH000010: On release of batch it still contained JDBC statements
Jun 18, 2015 3:10:34 PM com.vaadin.server.DefaultErrorHandler doDefault

Now my question, why is the first call okay and the duplication is found, but on the second run not? Okay I can catch the Exception which is thrown at the commit() function, but then, how could I remove the JDBC statements that remains?

Thanks, Josh

Answer 1

I got the answer. Here for everyone who gets the same Error:

Just add a merge operation before the persist operation.

PS: I don't know why this question got down votes, because its a legitimate question. The Javadoc of persist says:

Make an instance managed and persistent.

It doesn't make it managed! It's trying to create it in the Database. So its first trying to persist it, then manage it. The Javadoc of merge says:

Merge the state of the given entity into the current persistence context.

It sounds like overwriting, so I thought you can't use it here.

Answer 2

You should call persist only for entities in a NEW/TRANSIENT state. Because you are suing assigned identifiers, you are better of using merge instead (because Hibernate cannot figure out if the supplied entity is NEW or DETACHED).

So instead of:

entityManager.persist(element);

use this:

entityManager.merge(element);