public static interface YY {
        Object id();
    }
    @Entity
    @Access(AccessType.FIELD)
    @Table(name = "X")
    public class X implements YY {
    
        @Id
        long id;
    
        protected X() {
            this.id = Test.orderId++;
        }
    
    
        @Override
        public Long id() {
            return id;
        }
        }
    
    public class YPK {
    
    
        private final Date date;
        private final Long x;
    
        public YPK(X x, Date date) {
            this.date = date;
            this.x = x.id();
        }
    
        @Override
        public boolean equals(Object arg0) {
            if (arg0 == this) {
                return true;
            } else if (arg0 instanceof YPK) {
                return date.equals(((YPK) arg0).date)
                    && x.equals(((YPK) arg0).x);
            }
            return false;
        }
    
        @Override
        public int hashCode() {
            return date.hashCode() ^ x.hashCode();
        }
    }
    
    @Entity
    @Access(AccessType.FIELD)
    @Table(name = "Y")
    @IdClass(YPK.class)
    public class Y implements YY {
    
        @Id
        @Temporal(TemporalType.TIMESTAMP)
        Date date;
    
    
        @Id
        @ManyToOne(cascade = CascadeType.ALL)
        private X x;
    
        public Y(X x) {
            this.x = x;
            date = new DateTime().toDate();
        }
    
        protected Y() {
        }
    
        @Override
        public YPK id() {
            return new YPK(x, date);
        }
    
    }
    
    public class Test {
    
    public static long orderId = 0;
    public static long customerId = 0;
    
    public static void main(String[] args) {
        Map<String, String> properties = new HashMap<String, String>(){
            {
            put("javax.persistence.jdbc.url", "jdbc:derby://localhost:1527/myDB;create=false;");
            put("javax.persistence.jdbc.driver", "org.apache.derby.jdbc.ClientDriver");
            put("javax.persistence.jdbc.user", "myDbUser");
            put("javax.persistence.jdbc.password", "passwd");
    //        put(""eclipselink.ddl-generation", "drop-and-create-tables");
            put(""eclipselink.ddl-generation", "none");
            }
        };
    
        EntityManagerFactory emf =
            Persistence.createEntityManagerFactory("myPersistenceUnit", properties);
        final EntityManager em = emf.createEntityManager();
    
        X x =  new X();;
        saveItem(em, X.class, x);
    
        Y y =  new Y(x);;
    
    
        Y y2 =  new Y(x);;
    
        saveItems(em, Y.class, Arrays.asList(y, y2));
        saveItems(em, Y.class, Arrays.asList(y, y2));
    
        Z z =  new Z(y2);;
        saveItems(em, Z.class, Arrays.asList(z));
    }
    
    private static <T extends YY> void saveItem(final EntityManager em,
            Class<T> clazz, T item) {
        synchronized(em) {
            EntityTransaction tx = em.getTransaction();
            saveItem(em, clazz, item, tx);
        }
    }
    
    private static <T extends YY> void saveItems(final EntityManager em,
            Class<T> clazz, Collection<T> items) {
        synchronized (em) {
            EntityTransaction tx = em.getTransaction();
            try {
                tx.begin();
                for (T item : items) {
                    saveItem(em, clazz, item, tx);
                }
                tx.commit();
            } finally {
                if (tx.isActive()) {
                    tx.rollback();
                }
            }
        }
    }
    
    private static <T extends YY> void saveItem(final EntityManager em,
                Class<T> clazz,T item, EntityTransaction tx) {
        Object id = item.id();
        T existing = em.find(clazz, id);
    
        if (existing != null) {
            em.merge(item);
        } else {
            em.persist(item);
        }
    }
    
}

    [EL Warning]: 2011-03-24 06:52:56.047--UnitOfWork(20391510)--Exception [EclipseLink-4002]
    (Eclipse Persistence Services -
        2.2.0.v20110202-r8913): org.eclipse.persistence.exceptions.DatabaseException
    Internal Exception: java.sql.SQLIntegrityConstraintViolationException:
    The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'SQL110324065226450' defined on 'X'.
     Error Code: -1 Call:
     INSERT IGNORE INTO X (ID) VALUES (?) 	bind => [1 parameter bound]
     Query: InsertObjectQuery(com.test.X@1b6101e)
     Exception in thread "main" javax.persistence.RollbackException: Exception 
    [EclipseLink-4002] (Eclipse Persistence Services -
        2.2.0.v20110202-r8913):
     org.eclipse.persistence.exceptions.DatabaseException
     Internal Exception: java.sql.SQLIntegrityConstraintViolationException:
     The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'SQL110324065226450' defined on 'X'.
     Error Code: -1 Call: INSERT IGNORE INTO X (ID) VALUES (?) 	bind => [1 parameter bound]
     Query: InsertObjectQuery(com.test.X@1b6101e) 	at
    org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commitInternal(EntityTransactionImpl.java:102)
    at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commit(EntityTransactionImpl.java:63)
    at com.test.Test.saveItems(Test.java:80)
    at com.test.Test.main(Test.java:56)