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.

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);
    }
}

Answer 2

What about defining

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

?

Answer 3

I think that the best solution is a user SQL statement for setting on delete action as follow:

CREATE TABLE table_name
(
  column1 datatype null/not null,
  column2 datatype null/not null,
  ...

  CONSTRAINT fk_column
     FOREIGN KEY (column1, column2, ... column_n)
     REFERENCES parent_table (column1, column2, ... column_n)
     ON DELETE SET NULL
);

when user deletes a row by other cascading delete where you use a table reference to this deleted row, you could not use hibernate solution and return SQL exception.