Exception on cascade of remove in a unidirectional @OneToMany

[Jonny Andersson]

I have defined a (MS SQL Server 2008) database for a phone book as following:

CREATE TABLE phonebook.Subscriber
( id SMALLINT PRIMARY KEY NOT NULL,
  name VARCHAR(32) NOT NULL )

CREATE TABLE phonebook.PhoneNumber
( id SMALLINT PRIMARY KEY NOT NULL,
  number VARCHAR(16) UNIQUE NOT NULL,
  subscriber SMALLINT NOT NULL
  CONSTRAINT fk_PhoneNumber_Subscriber_id FOREIGN KEY (subscriber) REFERENCES phonebook.Subscriber (id) )

Note that the DBA (which is me ) have decided that a subscriber that not have any phone numbers may exist but a phone number must always have a subscriber, that is, the foreign key in PhoneNumber for a subscriber must not be null!

The code in an application that executes this phonebook have this method for remove of a subscriber:

    public void removeSubscriber(final Subscriber subscriber)
    {
        em.getTransaction().begin();
        em.remove(subscriber);
        em.getTransaction().commit();
    }

The relation between a subscriber and a phone number is defined as a unidirectional one-to-many relation in subscriber like this

    /** The list of phone numbers for this {@code Subscriber}. */
    @OneToMany(cascade = { CascadeType.PERSIST, CascadeType.REMOVE })
    @JoinColumn(name = "subscriber")
    private List<PhoneNumber> phoneNumberList;

Note that remove of a subscriber should cascade to its phone numbers. When a subscriber is removed should all the phone numbers also be removed.

When the remove is committed in the removeSubscriber method is an exception thrown:

<openjpa-2.1.0-SNAPSHOT-r422266:1030235 fatal store error> org.apache.openjpa.persistence.EntityExistsException:
Cannot insert the value NULL into column 'subscriber', table 'dev.phonebook.PhoneNumber'; column does not allow nulls.
UPDATE fails. {prepstmnt 877999189 UPDATE PhoneNumber SET subscriber = ? WHERE subscriber = ? [params=?, ?]}
[code=515, state=23000]

I am currently reading the good book Pro JPA 2: Mastering the Java Persistence API but I have not yet read anything about what the rule is for a situation like that above. To get the application work do I have to make the foreign key subscriber in the PhoneNumber table nullable but I don't know if it is because of a bug in the OpenJPA 2.1 implementation I use or if it is specified to work this way in the JPA 2 specification.

Does anyone know which of those alternatives is true?

In my opinion should I not have to customize the design of the database lika that. Instead should the entity manager in this case with a cascading remove first just remove the phone number and then without any problem remove the subscriber.