Cascading is about persistence actions involving one object propagating to other objects via an association. Cascading can apply to a variety of Hibernate actions, and it is typically transitive.
The "cascade=..." attribute of the annotation that defines the association says what actions should cascade for that association.
JPA allows you to propagate the state transition from a parent entity to a child. For this purpose, the JPA javax.persistence.CascadeType defines various cascade types:
ALL - cascades all entity state transitions
PERSIST - cascades the entity persist operation.
MERGE - cascades the entity merge operation.
REMOVE - cascades the entity remove operation.
REFRESH - cascades the entity refresh operation.
DETACH - cascades the entity detach operation.
Additionally, the CascadeType.ALL will propagate any Hibernate-specific operation, which is defined by the org.hibernate.annotations.CascadeType enum:
SAVE_UPDATE - cascades the entity saveOrUpdate operation.
REPLICATE - cascades the entity replicate operation.
LOCK - cascades the entity lock operation.
Cascading only makes sense only for Parent-Child associations (the Parent entity state transition being cascaded to its Child entities). Cascading from Child to Parent is not very useful and usually, it’s a mapping code smell.
The following examples will explain some of the aforementioned cascade operations using the following entities:
@Entity
public class Person {
@Id
private Long id;
private String name;
@OneToMany(mappedBy = "owner", cascade = CascadeType.ALL)
private List < Phone > phones = new ArrayList < > ();
//Getters and setters are omitted for brevity
public void addPhone(Phone phone) {
this.phones.add(phone);
phone.setOwner(this);
}
}
@Entity
public class Phone {
@Id
private Long id;
@Column(name = "`number`")
private String number;
@ManyToOne(fetch = FetchType.LAZY)
private Person owner;
//Getters and setters are omitted for brevity
}
