如何在多对多关系上使用休眠和 JPA 删除孤立实体？

摘自《Pro JPA 2》一书：

只有源端具有单基数的关系才能启用孤立项删除，这就是为什么在@OneToOne和@OneToMany关系批注上定义 orphanRemoval 选项，但在@ManyToOne或@ManyToMany批注上定义的原因。

这很糟糕，但是 ManyToMany 没有 JPA 自动删除孤立项。

实际上，我对以下实体进行了测试：

@Entity
public class Person {
    @Id
    @GeneratedValue
    private Long id;
    private String firstName;
    private String lastName;

    @ManyToMany
    @Cascade(value = org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
    private Set<Role> roles = new HashSet<Role>();

    //...
}

@Entity
public class Role {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @ManyToMany(mappedBy = "roles")
    private Set<Person> persons = new HashSet<Person>();

    //...
}

并使用以下数据集：

<dataset>
    <PERSON id="1" firstname="john" lastname="doe"/>
    <PERSON id="2" firstname="clark" lastname="kent"/>
    <PERSON id="3" firstname="james" lastname="bond"/>
    <ROLE id="1" name="foo"/>
    <ROLE id="2" name="bar"/>
    <ROLE id="3" name="boo"/>
    <ROLE id="4" name="baz"/>
    <PERSON_ROLE persons_id="1" roles_id="1"/>
    <PERSON_ROLE persons_id="1" roles_id="2"/>
    <PERSON_ROLE persons_id="2" roles_id="2"/>
    <PERSON_ROLE persons_id="2" roles_id="3"/>
    <PERSON_ROLE persons_id="3" roles_id="1"/>
    <PERSON_ROLE persons_id="3" roles_id="4"/>
</dataset>

以下测试方法：

@Test
public void testCascadeDeleteOrphanOnDelete() {
    Person person = entityManager.find(Person.class, 1L);
    entityManager.remove(person);
    ReflectionAssert.assertPropertyLenientEquals("id", Arrays.asList(2, 3), findAllPersons());
    ReflectionAssert.assertPropertyLenientEquals("id", Arrays.asList(3, 4), findAllRoles());

}

private List<Person> findAllPersons() {
    return entityManager.createQuery("from Person").getResultList();
}

private List<Role> findAllRoles() {
    return entityManager.createQuery("from Role").getResultList();
}

只是通过。在生产的输出下方：

Hibernate: select personx0_.id as id17_0_, personx0_.firstName as firstName17_0_, personx0_.lastName as lastName17_0_ from Person personx0_ where personx0_.id=?
Hibernate: select roles0_.persons_id as persons1_1_, roles0_.roles_id as roles2_1_, rolex1_.id as id18_0_, rolex1_.name as name18_0_ from Person_Role roles0_ left outer join Role rolex1_ on roles0_.roles_id=rolex1_.id where roles0_.persons_id=?
Hibernate: delete from Person_Role where persons_id=?
Hibernate: delete from Role where id=?
Hibernate: delete from Role where id=?
Hibernate: delete from Person where id=?
Hibernate: select personx0_.id as id17_, personx0_.firstName as firstName17_, personx0_.lastName as lastName17_ from Person personx0_
Hibernate: select rolex0_.id as id18_, rolex0_.name as name18_ from Role rolex0_