JPA cascade

We can use this 영속성 전이 transitive persistence functionality when we make a specific entity as managed state by EM and want the related entities to be managed as well. For example, when we save parent entity, we want to save child entity at the same time for convenience.

BTW, remember that for JPA to save entities, ALL related entities have to be in managed state

Without cascade, we need to do for example in bidirectional:

em.persist(parent)

child1.setParent(parent) //child -> parent 연관관계 설정
parent.getChildren().add(child1) //parent -> child 연관관계 설정
em.persist(child)

But with cascade like

@OneToMany(mappedBy=”parent”, cascade = PERSIST)
Private List<Child> children = new ArrayList<>();

child1.setParent(parent) //child -> parent 연관관계 설정
parent.getChildren().add(child1) //parent -> child 연관관계 설정
em.persist(parent)

//no em.persist(child)

remember that for JPA to save entities, ALL related entities have to be in managed state. Without cascade, we have to manually separately make parent and child entities as managed by persisting them. But using CascadeType.PERSIST, when parent entity is in managed state by persisting, all the related entities (child entities in this case) are all converted to managed state (persisted) in 1 go. Cascade provides the convenience that when an entity is persisted, other related entities are persisted also.

Same logic for REMOVE

We can put parameter ALL that has all properties of cascade

CascadeType.ALL

  • cascade = CascadeType.ALL declared for orderItems and delivery, which means when order is persisted, its collection which includes orderItems and delivery entity are also persisted into database. So there is no need to create those 2 repositories.

  • cascade = CascadeType.ALL should be used when entity is called only by one final entity like order. If it is called by more than 1 entity, then should not be used.

orderRepository.save(order)
// no need to save other entities that are linked with order like
//memberRepository.save(member);
//itemRepository.save(item);

difference between cascade.remove and orphanRemoval = true

They both manage persistence of related entities when a parent entity is removed. However there is a difference

Cascade.remove propagates (전이) removal operation from parent to connected child entities. Useful to ensure all related entities are deleted when a parent entity is deleted

Orphan removal removes child entity when they are no longer associated with a parent entity. It means when I remove a child entity from a parent’s collection, that child entity will be deleted from DB. Useful to ensure child entities sare persisted only if they are associated with a parent entity

all + orphanRemoval = true

Through parent entity, we can control 생명주기 lifecycle of child entity. For example if we want to remove child, we can remove via parent

Parent parent = em.find(Parent.class, parentId) parent.getChildren().remove(removeObject)