How To Batch Deletes In MySQL Via orphanRemoval=true
Description: Batch deletes in MySQL via orphanRemoval=true.
Note: Spring deleteAllInBatch() and deleteInBatch() don't use batching and don't take advantage of orphanRemoval=true. They trigger bulk operations and the persistent context is not synchronized accordingly. The first one simply triggers a delete from entity_name statement, while the second one triggers a delete from entity_name where id=? or id=? or id=? ... statement. Using these methods for deleting parent-entities and the associated entites (child-entities) requires explicit calls for both sides. For batching rely on deleteAll(), deleteAll(Iterable<? extends T> entities) or even better, on delete() method. Behind the scene, deleteAll() methods uses delete(). The delete() and deleteAll() methods rely on EntityManager.remove(), therefore, the persistent context is synchronized.
Key points for using deleteAll()/delete():
- in this example, we have a Author entity and each author can have several Book (one-to-many)
- first, we use orphanRemoval=true and CascadeType.ALL
- second, we dissociate all Book from the corresponding Author
- third, we explicitly (manually) flush the persistent context; is time for orphanRemoval=true to enter into the scene; thanks to this setting, all disassociated books will be deleted; the generated DELETE statements are batched (if orphanRemoval is set to false, a bunch of updates will be executed instead of deletes
- forth, we delete all Author via the deleteAll() or delete() method (since we have dissaciated all Book, the Author deletion will take advantage of batching as well)
