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

Question

我已经能够让 JPA/Hibernate 成功复制 ON DELETE CASCADE 功能(似乎是默认行为)，但我现在正在尝试复制 ON DELETE SET NULL 功能，我遇到了问题。

这是我的两个类(class):

@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，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.

我做错了吗？是不是可以实现？

谢谢。

Answer 1

目前使用 jpa/hibernate 似乎不可能。

On delete set null in hibernate in @OneToMany

JBs 的解决方案看起来很干净:

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

您还应该能够将其放入 PreRemove:

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