让JPA / Hibernate复制“ON DELETE SET NULL”功能 [英] Have JPA/Hibernate to replicate the "ON DELETE SET NULL" functionality

问题描述

我已经能够让JPA / Hibernate成功复制 ON DELETE CASCADE 功能（看起来像默认行为），但我现在试图复制 ON DELETE SET NULL 功能和我遇到问题。

这些是我的两个类：

  @Entity 
 @Table（name =teacher）
 public class Teacher 
 {
 @Id 
 @GeneratedValue 
 @Column（name =id，nullable = false，length = 4）
 private int id; 
 
 @OneToMany（mappedBy =teacher）
私人列表< Student> studentList; 
 
 // ... 
} 
  

---

  @Entity 
 @Table（name =student）
 public class Student 
 {
 @Id 
 @GeneratedValue 
 @Column（name =id，nullable = false，length = 4）
 private int id; 
 
 @ManyToOne（可选= true）
 @JoinColumn（name =teacher_id，nullable = true）
私人教师老师; 
 
 // ... 
} 
  

当我尝试要删除教师，会出现以下错误：

org.springframework.dao.DataIntegrityViolationException：无法执行JDBC批更新; SQL [从老师的teacher_id =？删除];约束[null]

...

引起：org.hibernate.exception.ConstraintViolationException：无法执行JDBC批量更新

.. 。
导致：java.sql.BatchUpdateException：批项0从teacher_id ='1'被中止的位置删除。调用getNextException来查看原因。

我做错了什么？它是可以实现的吗？

谢谢。

解决方案

目前用jpa / hibernate似乎不可能。

关于@OneToMany中的hibernate中的delete set null

JBs解决方案看起来很干净：

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

您应该也可以将它放入PreRemove中：

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

I've been able to have JPA/Hibernate to replicate the ON DELETE CASCADE functionality successfully (seems like the default behaviour) but I'm now trying to replicate the ON DELETE SET NULL functionality and I'm facing problems.

These are my two classes:

@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;

    // ...
}

When I try to delete a teacher, the following error appears:

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.

Am I doing something wrong? Is it something achievable?

Thank you.

解决方案

It doesn't appear to be possible at the moment with jpa/hibernate.

On delete set null in hibernate in @OneToMany

JBs solution seems clean though:

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

You should also be able to put it in a PreRemove:

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

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