@Cascade
The @Cascade annotation is used to apply the Hibernate specific CascadeType strategies (e.g. CascadeType.LOCK, CascadeType.SAVE_UPDATE, CascadeType.REPLICATE) on a given association.For JPA cascading, prefer using the javax.persistence.CascadeType instead.
When combining both JPA and Hibernate CascadeType strategies, Hibernate will merge both sets of cascades.
Cascade Apply a cascade strategy on an association. Used to apply Hibernate specific cascades. For JPA cascading, prefer using CascadeType on OneToOne, OneToMany, etc. Hibernate will merge together both sets of cascades.
Cascading entity state transitions
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.
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
}
CascadeType.PERSIST
The CascadeType.PERSIST allows us to persist a child entity along with the parent one.Example 360. CascadeType.PERSIST example
Person person = new Person();
person.setId( 1L );
person.setName( "John Doe" );
Phone phone = new Phone();
phone.setId( 1L );
phone.setNumber( "123-456-7890" );
person.addPhone( phone );
entityManager.persist( person );
INSERT INTO Person ( name, id )
VALUES ( 'John Doe', 1 )
INSERT INTO Phone ( `number`, person_id, id )
VALUE ( '123-456-7890', 1, 1 )
Even if just the Person parent entity was persisted, Hibernate has managed to cascade the persist operation to the associated Phone child entity as well.
CascadeType.MERGE
The CascadeType.MERGE allows us to merge a child entity along with the parent one.Example 361. CascadeType.MERGE example
Phone phone = entityManager.find( Phone.class, 1L );
Person person = phone.getOwner();
person.setName( "John Doe Jr." );
phone.setNumber( "987-654-3210" );
entityManager.clear();
entityManager.merge( person );
SELECT
p.id as id1_0_1_,
p.name as name2_0_1_,
ph.owner_id as owner_id3_1_3_,
ph.id as id1_1_3_,
ph.id as id1_1_0_,
ph."number" as number2_1_0_,
ph.owner_id as owner_id3_1_0_
FROM
Person p
LEFT OUTER JOIN
Phone ph
on p.id=ph.owner_id
WHERE
p.id = 1
During merge, the current state of the entity is copied onto the entity version that was just fetched from the database. That’s the reason why Hibernate executed the SELECT statement which fetched both the Person entity along with its children.
CascadeType.REMOVE
The CascadeType.REMOVE allows us to remove a child entity along with the parent one. Traditionally, Hibernate called this operation delete, that’s why the org.hibernate.annotations.CascadeType provides a DELETE cascade option. However, CascadeType.REMOVE and org.hibernate.annotations.CascadeType.DELETE are identical.Example 362. CascadeType.REMOVE example
Person person = entityManager.find( Person.class, 1L );
entityManager.remove( person );
DELETE FROM Phone WHERE id = 1
DELETE FROM Person WHERE id = 1
CascadeType.DETACH
CascadeType.DETACH is used to propagate the detach operation from a parent entity to a child.CascadeType.DETACH example
Person person = entityManager.find( Person.class, 1L );assertEquals( 1, person.getPhones().size() );
Phone phone = person.getPhones().get( 0 );
assertTrue( entityManager.contains( person ));
assertTrue( entityManager.contains( phone ));
entityManager.detach( person );
assertFalse( entityManager.contains( person ));
assertFalse( entityManager.contains( phone ));
CascadeType.LOCK
Although unintuitively, CascadeType.LOCK does not propagate a lock request from a parent entity to its children. Such a use case requires the use of the PessimisticLockScope.EXTENDED value of the javax.persistence.lock.scope property.However, CascadeType.LOCK allows us to reattach a parent entity along with its children to the currently running Persistence Context.
CascadeType.LOCK example
Person person = entityManager.find( Person.class, 1L );assertEquals( 1, person.getPhones().size() );
Phone phone = person.getPhones().get( 0 );
assertTrue( entityManager.contains( person ) );
assertTrue( entityManager.contains( phone ) );
entityManager.detach( person );
assertFalse( entityManager.contains( person ) );
assertFalse( entityManager.contains( phone ) );
entityManager.unwrap( Session.class )
.buildLockRequest( new LockOptions( LockMode.NONE ) )
.lock( person );
assertTrue( entityManager.contains( person ) );
assertTrue( entityManager.contains( phone ) );
CascadeType.REFRESH
The CascadeType.REFRESH is used to propagate the refresh operation from a parent entity to a child. The refresh operation will discard the current entity state, and it will override it using the one loaded from the database.CascadeType.REFRESH example
Person person = entityManager.find( Person.class, 1L );Phone phone = person.getPhones().get( 0 );
person.setName( "John Doe Jr." );
phone.setNumber( "987-654-3210" );
entityManager.refresh( person );
assertEquals( "John Doe", person.getName() );
assertEquals( "123-456-7890", phone.getNumber() );
SELECT
p.id as id1_0_1_,
p.name as name2_0_1_,
ph.owner_id as owner_id3_1_3_,
ph.id as id1_1_3_,
ph.id as id1_1_0_,
ph."number" as number2_1_0_,
ph.owner_id as owner_id3_1_0_
FROM
Person p
LEFT OUTER JOIN
Phone ph
ON p.id=ph.owner_id
WHERE
p.id = 1
In the aforementioned example, you can see that both the Person and Phone entities are refreshed even if we only called this operation on the parent entity only.
CascadeType.REPLICATE
The CascadeType.REPLICATE is to replicate both the parent and the child entities. The replicate operation allows you to synchronize entities coming from different sources of data.CascadeType.REPLICATE example
Person person = new Person();person.setId( 1L );
person.setName( "John Doe Sr." );
Phone phone = new Phone();
phone.setId( 1L );
phone.setNumber( "(01) 123-456-7890" );
person.addPhone( phone );
entityManager.unwrap( Session.class ).replicate( person, ReplicationMode.OVERWRITE );
SELECT
id
FROM
Person
WHERE
id = 1
SELECT
id
FROM
Phone
WHERE
id = 1
UPDATE
Person
SET
name = 'John Doe Sr.'
WHERE
id = 1
UPDATE
Phone
SET
"number" = '(01) 123-456-7890',
owner_id = 1
WHERE
id = 1
As illustrated by the SQL statements being generated, both the Person and Phone entities are replicated to the underlying database rows.
@OnDelete cascade
While the previous cascade types propagate entity state transitions, the @OnDelete cascade is a DDL-level FK feature which allows you to remove a child record whenever the parent row is deleted.So, when annotating the @ManyToOne association with @OnDelete( action = OnDeleteAction.CASCADE ), the automatic schema generator will apply the ON DELETE CASCADE SQL directive to the Foreign Key declaration, as illustrated by the following example.
@OnDelete @ManyToOne mapping
@Entity(name = "Person")public static class Person {
@Id
private Long id;
private String name;
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
@Column(name = "`number`")
private String number;
@ManyToOne(fetch = FetchType.LAZY)
@OnDelete( action = OnDeleteAction.CASCADE )
private Person owner;
//Getters and setters are omitted for brevity
}
create table Person (
id bigint not null,
name varchar(255),
primary key (id)
)
create table Phone (
id bigint not null,
"number" varchar(255),
owner_id bigint,
primary key (id)
)
alter table Phone
add constraint FK82m836qc1ss2niru7eogfndhl
foreign key (owner_id)
references Person
on delete cascade
Now, you can just remove the Person entity, and the associated Phone entities are going to be deleted automatically via the Foreign Key cascade.
@OnDelete @ManyToOne delete example
Person person = entityManager.find( Person.class, 1L );entityManager.remove( person );
delete from Person where id = ?
-- binding parameter [1] as [BIGINT] - [1]
The @OnDelete annotation can also be placed on a collection, as illustrated in the following example.
@OnDelete @OneToMany mapping
@Entity(name = "Person")public static class Person {
@Id
private Long id;
private String name;
@OneToMany(mappedBy = "owner", cascade = CascadeType.ALL)
@OnDelete(action = OnDeleteAction.CASCADE)
private List<Phone> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static 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
}
Now, when removing the Person entity, all the associated Phone child entities are deleted via the Foreign Key cascade even if the @OneToMany collection was using the CascadeType.ALL attribute.
@OnDelete @ManyToOne delete example
Person person = entityManager.find( Person.class, 1L );entityManager.remove( person );
delete from Person where id = ?
-- binding parameter [1] as [BIGINT] - [1]
Without the @OnDelete annotation, the @OneToMany association relies on the cascade attribute to propagate the remove entity state transition from the parent entity to its children. However, when the @OnDelete annotation is in place, Hibernate prevents the child entity DELETE statement from being executed while flushing the Persistence Context.
This way, only the parent entity gets deleted, and all the associated child records are removed by the database engine, instead of being deleted explicitly via DELETE statements.
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