Transactional method not write updates on database - mysql

Question

I'm working on a Spring application that uses Hibernate 4.3 to manage data stored in a MySql database.
I want to simply update the value of this object:
#Table(name = "CONTENT")
public class KcContent {
#Id
#GeneratedValue
#Column(name = "ID")
#DocumentId
private Long id;
#Column(name="PRIORITY")
private Long priority;
// getter and setter
}
This is the point where I update the object:
private EntityManager entityManager;
#Transactional
public String checkAndManageActionsNewsletter(NewsletterActionRequestBean requestBean) {
List<String> newsIds = requestBean.getNewsIds();
// update priority based on position in list
for(long priority = 0; priority < newsIds.size(); priority++) {
String newsId = newsIds.get((int) priority);
long contentId = Long.parseLong(newsId);
KcContent news = getServiceCatalog().getContentService().find(contentId);
news.setPriority(priority);
}
}
Where #Transactional is imported from org.springframework.transaction.annotation.Transactional.
This code results in no update on database. I also tried to add after setPriority():
this.entityManager.merge(news)
this.entityManager.persist(news)
but it doesn't work.
I checked the reference to the object in the entityManager after the setPriority() method, and the value it's updated.
In the database instead the value is still the old value (0):
In the end, I tried to change values on database for the priority, and the application read them correctly, so the problem seems to be only on update.
There is some mistakes in the configuration?
Note: unfortunately I can't use JpaRepository.
Update:
This is the implementation of the find() method in the ContentService class:
public EntityManager getEntityManager() {
return entityManager;
}
#PersistenceContext
public void setEntityManager(EntityManager entityManager) {
this.entityManager = entityManager;
}
#Override
#Transactional(readOnly=true)
public KcContent find(Long id) {
if (id == null){
return null;
}
return getEntityManager().find(KcContent.class, id);
}