java - 一对一关系 hibernate 导致许多查询

Question

我有一对一关系的下课

@Entity
@Table(name = "PERSON")
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "PERSON_ID")
    private int personId;
    @Column(name = "PERSON_NAME", nullable = false, length = 30)
    private String personName;
    @OneToOne(mappedBy = "person", cascade = CascadeType.ALL)
    private DrivingLicense drivingLicense;
}

@Entity
@Table(name = "DRIVING_LICENSE")
public class DrivingLicense {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "LICENSE_NUMBER")
    private int licenseNumber;
    @Column(name = "DATE_OF_ISSUE")
    private Date dateOfIssue;
    @OneToOne
    @JoinColumn(name = "PERSON_ID", unique = true)
    private Person person;
}

目前每个表有3行

但是当我像下面这样对 person 进行查询时

Query query = entityManager.createQuery("from Person p");

在获得结果列表后，它导致了太多的查询，如下所示；

Hibernate: select person0_.PERSON_ID as PERSON_ID1_1_, person0_.PERSON_NAME as PERSON_NAME2_1_ from PERSON person0_
Hibernate: select drivinglic0_.LICENSE_NUMBER as LICENSE_NUMBER1_0_1_, drivinglic0_.DATE_OF_ISSUE as DATE_OF_ISSUE2_0_1_, drivinglic0_.PERSON_ID as PERSON_ID3_0_1_, person1_.PERSON_ID as PERSON_ID1_1_0_, person1_.PERSON_NAME as PERSON_NAME2_1_0_ from DRIVING_LICENSE drivinglic0_ left outer join PERSON person1_ on drivinglic0_.PERSON_ID=person1_.PERSON_ID where drivinglic0_.PERSON_ID=?
Hibernate: select drivinglic0_.LICENSE_NUMBER as LICENSE_NUMBER1_0_1_, drivinglic0_.DATE_OF_ISSUE as DATE_OF_ISSUE2_0_1_, drivinglic0_.PERSON_ID as PERSON_ID3_0_1_, person1_.PERSON_ID as PERSON_ID1_1_0_, person1_.PERSON_NAME as PERSON_NAME2_1_0_ from DRIVING_LICENSE drivinglic0_ left outer join PERSON person1_ on drivinglic0_.PERSON_ID=person1_.PERSON_ID where drivinglic0_.PERSON_ID=?
Hibernate: select drivinglic0_.LICENSE_NUMBER as LICENSE_NUMBER1_0_1_, drivinglic0_.DATE_OF_ISSUE as DATE_OF_ISSUE2_0_1_, drivinglic0_.PERSON_ID as PERSON_ID3_0_1_, person1_.PERSON_ID as PERSON_ID1_1_0_, person1_.PERSON_NAME as PERSON_NAME2_1_0_ from DRIVING_LICENSE drivinglic0_ left outer join PERSON person1_ on drivinglic0_.PERSON_ID=person1_.PERSON_ID where drivinglic0_.PERSON_ID=?

很明显，为了获取 3 行，hibernate 触发了 4 个查询，如何解决这个问题？我在人际关系方面做错了什么吗？

更新

现在如果我像这样获取驾驶执照

Query query = entityManager.createQuery("from DrivingLicense dl");

更糟糕的是，触发了 7 个查询。

Answer 1

要拥有独立于 JPA 供应商的解决方案，您可以使用以下 JPQL 查询。

获取所有拥有DrivingLicense的Person

Query query = entityManager.createQuery("from Person p join fetch p.drivingLicense");

让所有 Person 独立，无论他们是否有 DrivingLicense

Query query = entityManager.createQuery("from Person p left join fetch p.drivingLicense");

或使用Criteria API

CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
CriteriaQuery<Person> criteriaQuery = criteriaBuilder.createQuery(Person.class);
Root<Person> root = criteriaQuery.from(Person.class);
root.fetch("drivingLicense", JoinType.INNER);
criteriaQuery.select(root);
List<Person> resultList = em.createQuery(criteriaQuery).getResultList();

回复

CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
CriteriaQuery<Person> criteriaQuery = criteriaBuilder.createQuery(Person.class);
Root<Person> root = criteriaQuery.from(Person.class);
root.fetch("drivingLicense", JoinType.LEFT);
criteriaQuery.select(root);
List<Person> resultList = em.createQuery(criteriaQuery).getResultList();