Bidrectional #OneToMany relation with a composite key - jpa

Question

I have been trying to create a bidirectional #OneToMany relation with composite keys but some pieces are missing or wrong.
I have a draft entity which holds a list of sub draft entities.
Here is what I got:
#Entity
#Table(name = "draft")
#IdClass(Pk.class)
public class Draft {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
protected Long id;
#Id
protected Integer rev;
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "draft")
List<SubDraft> subDrafts = new ArrayList<SubDraft>();
// getters / setters omitted
}
#Entity
#Table(name = "sub_draft")
#IdClass(PK.class)
public class DraftToDoDAO {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
protected Long id;
#Id
protected Integer rev;
#ManyToOne(fetch = FetchType.LAZY)
#PrimaryKeyJoinColumns({
#PrimaryKeyJoinColumn(name = "draft_id", referencedColumnName = "id"),
#PrimaryKeyJoinColumn(name = "draft_rev", referencedColumnName = "rev")
})
protected DraftDAO draft;
// getters / setters omitted
}
public class PK implements Serializable {
protected Long id;
protected Integer rev;
public PK() {
}
public PK(Long id, Integer rev) {
this.id = id;
this.rev = rev;
}
public Long getId() {
return id;
}
public Integer getRev() {
return rev;
}
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((id == null) ? 0 : id.hashCode());
result = prime * result + ((rev == null) ? 0 : rev.hashCode());
return result;
}
#Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
MetaDataDAO other = (MetaDataDAO) obj;
if (id == null) {
if (other.id != null)
return false;
} else if (!id.equals(other.id))
return false;
if (rev == null) {
if (other.rev != null)
return false;
} else if (!rev.equals(other.rev))
return false;
return true;
}
}
I have no problems saving a draft with a list of sub drafts but the relation is not created both ways.
In the sub draft table the SchemaTool (DataNucleus) creates a column named draft_id but it is empty. And I wonder why it is not creating the columns I specified (draft_id, draft_rev) and settles the relation there.
I have search a lot for an answer but just can not get thing to work.
Your help is appreciated!
Thanks.
EDIT!
Here is the actual persistence code:
public Draft create(Draft draft, SubDraft subDraft) {
EntityManager em = PersistenceHelper.getEntityManager();
draft.setCreated(Calendar.getInstance());
// This should do it
draft.setSubDraft(subDraft);
subDraft.setDraft(draft);
em.persist(draft);
em.close();
return draft;
}

Answer 1

Some where along the line of code this subDraft attribute was nilled and therefore is did not work.