java - 删除实体时违反约束

Question

我正在与 hibernate 作斗争。我正在尝试删除对象，但遇到 sql 异常。

首先是我的映射:

@Entity
public class Meetup {

    @Id
    @GeneratedValue
    @Column
    private long id;

    @Column(nullable = false)
    private ZonedDateTime dateAndTime;

    @ManyToOne(fetch = FetchType.EAGER,cascade=CascadeType.PERSIST)
    private Location location;

/////////////////////////

@Entity
public class Location {

    @Id
    @GeneratedValue
    @Column
    private long id;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false)
    private double longitude;

    @Column(nullable = false)
    private double latitude;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "location")
    private List<Meetup> meetups;

///////////////////////////////////////////////////////

@Entity
public class Match {
    @Id
    @GeneratedValue
    @Column
    private long id;

    @ManyToMany(fetch = FetchType.LAZY, cascade=CascadeType.ALL)
    private List<User> users = new ArrayList<>();

    @OneToOne(cascade=CascadeType.ALL)
    @JoinColumn(name = "meetup_id")
    private Meetup meetup;

所以我试图删除聚会实体，但这样做我不想删除相应的位置实体。现在，当我尝试删除 meetup 实体 (entityManager.remove) 时，我得到

 constraint ["FKJRLUYUGNHRKYWSVSRE8VE9I9D: PUBLIC.MATCH FOREIGN KEY(MEETUP_ID) REFERENCES PUBLIC.MEETUP(ID) (1)"; SQL statement: delete from meetup where id=? [23503-192]]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement

可以通过在 meetup 类中的映射上将 Cascade 类型更改为“ALL”来解决该问题，但显然我的 Location 实体也会被删除。这是我不希望发生的事情。那么如何才能实现删除聚会实体而不删除位置实体呢？

Answer 1

您只需确保在事务范围内按如下方式处理 MeetUp 的删除:

// Get your meetup by identifier
final Meetup meetup = entityManager.find( Meetup.class, meetupId );

// cleanup the match associations with meetup
entityManager.createQuery( "FROM Match WHERE meetup = :meetup")
      .setParameter( "meetup", meetup )
      .getResultList()
      .forEach( match -> { match.setMeetup( null ); } );

// remove meetup
entityManager.remove( meetup );

根据您的模型，无需针对此用例使用级联操作。