【问题标题】：One to one relationship hibernate results in many queries一对一关系休眠导致许多查询
【发布时间】：2023-03-17 18:22:02
【问题描述】：

我在一对一的关系中有以下课程

@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;
}

目前每张表有3行

但是当我对person 进行如下查询时

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

在获取结果列表后，会导致以下查询过多；

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=?

显然是为了获取 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吗？

更新

现在，如果我拿驾照来拿，比如

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

更糟糕的是，触发了 7 个查询。

【问题讨论】：

您不仅应该显示实体之间的关系，还应该显示整个实体类。因为ID 列对于答案并非不重要。
@SubOptimal 添加了 id 列

标签： java oracle hibernate

【解决方案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。

使用DrivingLicense 获取所有Person

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

如果他们有DrivingLicense，则获取所有Person独立

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();

分别

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();

【讨论】：

【解决方案2】：

这似乎是由于您的查询，即

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

改为使用：

session.createCriteria();

这只会触发 1 个查询来获取 Person：

Hibernate：选择 this_.id 作为 id1_1_1_，this_.name 作为 name2_1_1_， drivinglic2_.id 作为 id1_0_0_，drivinglic2_.DL_no 作为 DL_no2_0_0_， drivinglic2_.PERSON_ID 作为 PERSON_I3_0_0_ 来自 PERSON this_ 左外在 this_.id=drivinglic2_.PERSON_ID 上加入 DRIVING_LICENSEdrivinglic2_ 按 this_.id asc 排序

【讨论】：