function saveOrderById(order){
    // get the order's items with pending changes
    var itemsWithChanges = order.orderItems().filter(
        function(item) { return item.entityAspect.isAddedModifiedOrDeleted()});
    // concatenate with the order itself (you may have a concurrency property to set, btw)
    var savables = itemsWithChanges.concat(order)
    return order.entityAspect.entityManager.saveChanges(savables); // returns the promise
}