更新

Question

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;
}

目前每个表中有3行

但当我对person进行查询时如下

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

获取结果列表后会产生如下所示的太多查询;

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=?

显然对于获取3行hibernate解雇了4个查询，如何解决这个问题？我在关系方面做错了吗？

更新

现在，如果我使用驾驶执照，如

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

更糟糕的是，7个查询被解雇。

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。

使用Person

获取所有DrivingLicense

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

如果他们有Person或不是

，则

让所有DrivingLicense符号相同

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();

RESP。

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();

Answer 2

这似乎是由于您的疑问，即

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

改为使用：

session.createCriteria();

这将只触发1个查询来获取Person：

休眠：选择this_.id为id1_1_1_，this_.name为name2_1_1_， drivinglic2_.id为id1_0_0_，drivinglic2_.DL_no为DL_no2_0_0_， drivinglic2_.PERSON_ID为PERSON_I3_0_0_来自PERSON this_ left outer 在this_.id = drivinglic2_.PERSON_ID上加入DRIVING_LICENSE drivinglic2_ 由this_.id asc
命令

一对一的关系hibernate导致许多查询

更新

2 个答案: