CODEWITHSUNDEEP
jpacachingentity
simonalexander2005
simonalexander2005

Reputation: 4577

Can you just clear specific entity types from JPA Entity Manager cache

In the raw JPA specification (so not a specific implementation like Hibernate or EclipseLink), is there an option to call em.clear() for a specific type of entity but not for others?

The reason I'm asking is, I have a process which creates and stores tens of thousands of entities; but each is not needed again by the entity manager after it's been persisted. However, each entity has a child entity which is one of about 30 records in the database. So I want to be able to call something like em.clear(MainEntity.class), meaning I don't clear the cache of the child entity which is reused, but also don't build up a history of tens of thousands of unneeded records.

Here's a simplified example of what I am currently doing:

List<Child> children = (List<Child>)em.createQuery("Select c from " + Child.entityName + " c").getResultList();

for (int i=0;i<700000;i++)
{
    Parent p = createParent(i, getRandomChild(children));
    em.persist(p);
    
    if (i%1000 == 0)
    {
         em.flush(); // push to db
         em.clear(); // remove old items from cache - but unfortunately removes children too
        // as I've cleared the cache, I need to repopulate this to reattach the children again
        children = (List<Child>)em.createQuery("Select c from " + Child.entityName + " c").getResultList();
    }
}

Upvotes: 0

Views: 634

Answers (1)

Lazaros Chatzimichalakis
Lazaros Chatzimichalakis

Reputation: 111

You can use

void detach(java.lang.Object entity)

like this

em.detach(p);

to remove only parent from the persistence context.

Upvotes: 1

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