在删除时使用外键设置为空

Question

在这种情况下，answer_id是评级表中的外键，而answer_id是答案表中的主键。我需要删除答案，但“无法删除或更新父行：外键约束失败。发生错误。如何为此外键设置 ON DELETE SET NULL 选项。

@Entity
@Table(name = "ratings")
public class Ratings {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long rating_id;

    @Column(nullable = false, unique = false, length = 45)
    private Short ratingValue;

    @ManyToOne(cascade = fetch = FetchType.LAZY)
    @JoinColumn(name = "userId")
    private User user;

    @ManyToOne(cascade = fetch = FetchType.LAZY)
    @JoinColumn(name = "answer_id")
    private Answer answer;

    @ManyToOne(cascade = fetch = FetchType.LAZY)
    @JoinColumn(name = "question_id")
    private Question question;
//getters and setters

@Entity
@Table(name = "answers")
public class Answer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long answer_id;

    @Column(nullable = false, unique = false, length = 100)
    private String fullAnswer;

    /*Many to one mapping question*/
    @ManyToOne(cascade = FetchType.LAZY)
    @JoinColumn(name = "question_id")
    private Question question;

    /* Many to One mapping with users*/
    @ManyToOne(cascade = FetchType.LAZY)
    @JoinColumn(name = "userId")
    private User user;
//getters and setters

Answer 1

Hibernate 不支持 SET NULL 操作。

该功能请求于 2006 年创建，目前仍处于“开放”状态。

• @OnDelete -> action = OnDeleteAction.SET_NULL（就像在 MySql 5 中一样）

解决方法是在父实体上创建一个

@PreRemove

方法，将子实体中的外键设置为 NULL。我想如果您添加其他子实体，您必须修改您的

@PreRemove

方法。请参阅此答案中的示例：

• 让 JPA/Hibernate 复制“ON DELETE SET NULL”功能

Answer 2

他们添加了这个。只要这样做：

@OnDelete(action = OnDeleteAction.SET_NULL)

休眠 jira HHH-15770