JPA persistence doing an insert instead of update on entitymanager.merge()

[transmeta01]

I have DAO methods annotated with @Transactional as such:

public abstract class GenericDAO<T> implements DAO<T> {

private Class<T> persistentClass;

@PersistenceContext

EntityManager em;

public GenericDAO(EntityManager em, Class<T> persistentClass) {

this.persistentClass = persistentClass;

this.em = em;

}

public GenericDAO(Class<T> persistentClass) {

this.persistentClass = persistentClass;

}

@Transactional

@Override

public T persist(T t) {

em.persist(t);

return t;

}

@Transactional

@Override

public void delete(T t) {

em.remove(t);

em.flush();

}

@Transactional

@Override

public T update(T t) {

em.merge(t);

return t;

}

@Transactional()

@Override

public T merge(T t) {

em.merge(t);

return t;

}

@Override

public T findById(Long id) {

return em.find(persistentClass, id);

}

}

When I call merge, the DAO does an insert (new row), instead of doing an update. What is there a specific scope the persistence context must be in order to the update to be done? BTW, I have tried with adding em.flush() after the call to em.merge(), but did not solve the problem.

Thank

[Wujek Srujek]

This is too little code to really say, the DAO itself is not enough, people normally needs some more context, but I suspect that the fact that you are ignoring the return value of merge might be causing your problems. The following scenario:

DomainObject do = new DomainObject(); // new state

dao.save(do); // here, the thing gets merged, which means a new instance is created and put in the persistence context and returned, and you ignore the returned result; unfortunately, do remains in new state, and it's the returned (and ignored) value that ist detached

do.setFoo(17);

dao.update(do); // here, you are not dealing with a detached instance, but again, a new one

Try to change the code so that the return value of merge does get used. Again, this is just a suspicion.

wujek

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[Richard Mutezintare]

good point about not returning the actual entity from merge method. I changed the method to return the result from merge(), however this did not solve the problem...

On Wed, Nov 21, 2012 at 4:13 PM, Wujek Srujek <wujek....@gmail.com> wrote:

here, the thing gets merged, which means a new instance is created an

I thought the entityManager would look at the id and if there is one, it would fetch the corresponding entity and then do the merging, if there is no id, then it is a persit() call? My problem may be because i essentially have no session, in the hibernate since, I suspect that a new persistence context is created by guice-persist every time, since my dao is not bound to a @Singleton scope...do this make since? In any case, I am investigating in that direction. Any alternate suggestions?

Thanks

[Richard Mutezintare]

after debugging turns out the persistence context sticks, in the code snippet below: 

@Transactional

@Override

public T merge(T t) {

boolean isManager = em.contains(t);

System.out.print(isManager);

t = em.merge(t);

return t;

}

isManaged = true, and yet, an insert is still performed instead of an update...Then tried adding em.flush(), still to no avail. 

below is my persistence.xml file: (it's pretty vanilla)

<persistence-unit name="logbook-persistence" transaction-type="RESOURCE_LOCAL">

<provider>org.hibernate.ejb.HibernatePersistence</provider>

<!-- transaction will be application managed in dev/test mode -->

<!-- <jta-data-source>java:/DefaultDS</jta-data-source> -->

<properties>

<property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" />

<property name="hibernate.hbm2ddl.auto" value="update" />

<!-- <property name="javax.persistence.validation.mode" value="NONE" /> -->

<property name="hibernate.show_sql" value="true" />

<property name="hibernate.format_sql" value="true" />

<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver" />

<property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/logbook" />

<property name="hibernate.connection.username" value="root" />

<property name="hibernate.connection.password" value="root" />

<property name="hibernate.connection.autocommit" value="true" />

<!-- <property name="hibernate.cache.use_query_cache" value="true"/> 

<property  name="hibernate.cache.use_second_level_cache" value="true"/> 

<property name="hibernate.cache.region.factory_class" 

value="org.hibernate.cache.infinispan.InfinispanRegionFactory"/> -->

<property name="hibernate.connection.provider_class" value="org.hibernate.connection.DriverManagerConnectionProvider" />

</properties>

</persistence-unit>