java - Have JPA/Hibernate to replicate the "ON DELETE SET NULL" functionality

Question

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.

question from:https://stackoverflow.com/questions/9944137/have-jpa-hibernate-to-replicate-the-on-delete-set-null-functionality

Answer 1

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);
    }
}