JPA: unidirectional many-to-one and cascading delete

Question

Say I have a unidirectional @ManyToOne relationship like the following:

@Entity
public class Parent implements Serializable {

    @Id
    @GeneratedValue
    private long id;
}

@Entity
public class Child implements Serializable {

    @Id
    @GeneratedValue
    private long id;

    @ManyToOne
    @JoinColumn
    private Parent parent;  
}

If I have a parent P and children C₁...C_n referencing back to P, is there a clean and pretty way in JPA to automatically remove the children C₁...C_n when P is removed (i.e. entityManager.remove(P))?

What I'm looking for is a functionality similar to ON DELETE CASCADE in SQL.

Answer 1

If you are using hibernate as your JPA provider you can use the annotation @OnDelete. This annotation will add to the relation the trigger ON DELETE CASCADE, which delegates the deletion of the children to the database.

Example:

public class Parent {

        @Id
        private long id;

}


public class Child {

        @Id
        private long id;

        @ManyToOne
        @OnDelete(action = OnDeleteAction.CASCADE)
        private Parent parent;
}

With this solution a unidirectional relationship from the child to the parent is enough to automatically remove all children. This solution does not need any listeners etc. Also a query like DELETE FROM Parent WHERE id = 1 will remove the children.