Duplicate a collection of entities and persist in Hibernate/JPA
- by Michael Bavin
Hi,
I want to duplicate a collection of entities in my database.
I retreive the collection with:
CategoryHistory chNew = new CategoryHistory();
CategoryHistory chLast = (CategoryHistory)em.createQuery("SELECT ch from CategoryHistory ch WHERE ch.date = MAX(date)").getSingleResult;
List<Category> categories = chLast.getCategories();
chNew.addCategories(categories)// Should be a copy of the categories: OneToMany
Now i want to duplicate a list of 'categories' and persist it with EntityManager.
I'm using JPA/Hibernate.
UPDATE
After knowing how to detach my entities, i need to know what to detach:
current code:
CategoryHistory chLast = (CategoryHistory)em.createQuery("SELECT ch from CategoryHistory ch WHERE ch.date=(SELECT MAX(date) from CategoryHistory)").getSingleResult();
Set<Category> categories =chLast.getCategories();
//detach
org.hibernate.Session session = ((org.hibernate.ejb.EntityManagerImpl) em.getDelegate()).getSession();
session.evict(chLast);//detaches also its child-entities?
//set the realations
chNew.setCategories(categories);
for (Category category : categories) {
category.setCategoryHistory(chNew);
}
//set now create date
chNew.setDate(Calendar.getInstance().getTime());
//persist
em.persist(chNew);
This throws a failed to lazily initialize a collection of role: entities.CategoryHistory.categories, no session or session was closed exception.
I think he wants to lazy load the categories again, as i have them detached. What should i do now?
