使用JPA/Hibernate来复制"ON DELETE SET NULL"功能

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使用JPA/Hibernate来复制"ON DELETE SET NULL"功能

我已经成功地使用JPA/Hibernate实现了ON DELETE CASCADE的功能（似乎是默认行为），但是我现在尝试复制ON DELETE SET NULL的功能，并且遇到了问题。

以下是我的两个类：

@Entity
@Table(name = "teacher")
public class Teacher {
    @Id
    @GeneratedValue
    @Column(name = "id", nullable = false, length = 4)
    private int id;
    @OneToMany(mappedBy = "teacher")
    private List studentList;
    // ...
}


@Entity
@Table(name = "student")
public class Student {
    @Id
    @GeneratedValue
    @Column(name = "id", nullable = false, length = 4)
    private int id;
    @ManyToOne(optional = true)
    @JoinColumn(name = "teacher_id", nullable = true)
    private Teacher teacher;
    // ...
}

当我尝试删除一个教师时，出现以下错误：

org.springframework.dao.DataIntegrityViolationException: Could not execute JDBC batch update; SQL [delete from teacher where teacher_id=?]; constraint [null]

...

Caused by: org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update

...

Caused by: java.sql.BatchUpdateException: Batch entry 0 delete from teacher where teacher_id='1' was aborted. Call getNextException to see the cause.

我做错了什么吗？是否有办法实现这个功能？

谢谢。

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