@Entity
public class Parent {
   private Long id = null;
   private int version = 0;
   private Child child;

   @Id @GeneratedValue
   public Long getId() {
      return id;
   }
   @SuppressWarnings("unused")  //used only by hibernate via reflection
   private void setId(Long id) {
      this.id = id;
   }

   @Version
   @SuppressWarnings("unused")  //used only by hibernate via reflection
   private int getVersion() {
      return version;
   }
   @SuppressWarnings("unused")  //used only by hibernate via reflection
   private void setVersion(int version) {
      this.version = version;
   }

   @ManyToOne(cascade = {CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH},
            fetch = FetchType.LAZY)
   @JoinColumn(nullable = false)
   @org.hibernate.annotations.ForeignKey(name = "fk_Parent_Child")
   public Child getChild() {
      return child;
   }
   public void setChild(Child child) {
      this.child = child;
   }
}

@Entity
@org.hibernate.annotations.Entity(dynamicInsert = true, dynamicUpdate = true) // faster updates and inserts
public class Child {
   private Long id = null;
   private int version = 0;

   @Id @GeneratedValue
   public Long getId() {
      return id;
   }
   @SuppressWarnings("unused")  //used only by hibernate via reflection
   private void setId(Long id) {
      this.id= id;
   }

   @Version
   @SuppressWarnings("unused")  //used only by hibernate via reflection
   private int getVersion() {
      return version;
   }
   @SuppressWarnings("unused")  //used only by hibernate via reflection
   private void setVersion(int version) {
      this.version = version;
   }
}

private void save()
   {
   if(!entityManager.contains(parent)
      {
      log.info("enter child.version={0}", child.getVersion());
      parent = entityManager.merge(parent);
      log.info("merge child.version={0}", child.getVersion());
      entityManager.persist(parent);
      log.info("persist child.version={0}", child.getVersion());
      // Add some objects to a container
      entityManager.flush();
      log.info("flush child.version={0}", child.getVersion());
      }
   }