How to Resolve the 'Detached Entity Passed to Persist' Error in Play Framework?

What does the 'detached entity passed to persist' error mean in Play Framework and how can it be resolved?

@Transactional
public void saveEntity(MyEntity entity) {
    entityManager.persist(entity);
}

The 'detached entity passed to persist' error in Play Framework typically occurs when an application attempts to persist an entity that is outside of the current persistence context. This usually happens after the entity was previously loaded from the database and is no longer managed by the EntityManager.

@Transactional
public MyEntity saveEntity(MyEntity entity) {
    return entityManager.merge(entity);
}

Causes

• The entity was detached from the current Hibernate session.
• The operation attempted to persist an entity that is already present in the DB context under a different entity manager.
• A transaction boundary was crossed without merging the entity.

Solutions

• Use the `merge` method instead of `persist` to reattach the entity to the current session.
• Ensure that the entity is managed within a transaction context when persisting.
• Review your transaction demarcation strategy to maintain correct entity states.

Mistake: Using `persist` on an entity that was previously detached.

Solution: Switch to `merge`, which can handle detached entities.

Mistake: Not managing entity states during transaction boundaries.

Solution: Ensure entities are either merged or unassociated with a prior context.