让JPA/Hibernate复制"ON DELETE SET NULL"功能

Question

我已经能够让JPA/Hibernate ON DELETE CASCADE成功复制功能(看起来像默认行为),但我现在正在尝试复制ON DELETE SET NULL功能,我遇到了问题.

这是我的两个班级:

@Entity
@Table(name = "teacher")
public class Teacher
{
    @Id
    @GeneratedValue
    @Column(name = "id", nullable = false, length = 4)
    private int id;

    @OneToMany(mappedBy = "teacher")
    private List<Student> 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;

    // ...
}

当我尝试删除教师时,会出现以下错误:

org.springframework.dao.DataIntegrityViolationException:无法执行JDBC批量更新; SQL [从老师那里删除teacher_id =？]; constraint [null]
...
引起:org.hibernate.exception.ConstraintViolationException:无法执行JDBC批量更新
...
由以下引起:java.sql.BatchUpdateException:批量输入0从教师中删除,其中teacher_id ='1'已中止.调用getNextException以查看原因.

难道我做错了什么？这是可以实现的吗？

谢谢.

Answer 1

目前用jpa/hibernate似乎不可能.

在@OneToMany中,在hibernate中删除set null

JBs解决方案似乎很干净:

for (Department child : parent.getChildren()) {
    child.setParentDepartment(null);
}
session.delete(parent);

你也应该能够把它放在PreRemove中:

@PreRemove
private void preRemove() {
    for (Student s : studentList) {
        s.setTeacher(null);
    }
}

Answer 2

怎么定义

@ForeignKey(name = "fk_student_teacher",
            foreignKeyDefinition = " /*FOREIGN KEY in sql that sets ON DELETE SET NULL*/")

?