Update values of multiple value field programmatically? (Rules action)

Question

I'm trying to create a rule to populate a multiple value order reference field in Drupal Commerce, on checkout complete.

I haven't been able to achieve this through Rules UI, so instead I'm trying to programmatically create the action but can't figure out how to set the actual value.

I simply want to add a reference of the newly created order to the purchased product, while keeping the references already set (in this particular case an order will never contain more than one product).

I have added an order_reference_field (Commerce Order Reference module) to my product, showing checkboxes with multiple values allowed.

Below my code:

function example_rules_action_info() {
  $actions = array();

  $actions['commerce_set_product_order_ref'] = array(
    'label' => t('Link an order to the purchased product'),
    'group' => t('Custom action'),
    'parameter' => array(
      'commerce_line_item' => array(
        'type' => 'commerce_line_item',
        'label' => t('Line item'),
      ),
    ),
  );

  return $actions;
}


function commerce_set_product_order_ref($line_item, $order) {
  if (in_array($line_item->type, commerce_product_line_item_types())) {

    $sku = $line_item->line_item_label;
    $product = commerce_product_load_by_sku($sku);
    $orderID = $line_item->order_id;

    $wrapper = entity_metadata_wrapper('commerce_product', $product);

    $wrapper->field_order_reference /***** What to do here? *******/

    $result = $wrapper->save();


  }
}

EDIT:

I have gotten a little further with the code below.. It works the first time an order reference is set, but the second time i get the following error "The website encountered an unexpected error. Please try again later."

Found the example a bit down this page: https://drupal.org/node/1021556

function example_rules_action_info() {
  $actions = array();

  $actions['commerce_set_product_order_ref'] = array(
    'label' => t('Link an order to the purchased Product'),
    'group' => t('Custom action'),
    'parameter' => array(
      'commerce_line_item' => array(
        'type' => 'commerce_line_item',
        'label' => t('Line item'),
      ),
    ),
  );

  return $actions;
}


function commerce_set_product_order_ref($line_item, $order) {
  if (in_array($line_item->type, commerce_product_line_item_types())) {

    $sku = $line_item->line_item_label;
    $product = commerce_product_load_by_sku($sku);
    $orderID = $line_item->order_id;
    $wrapper = entity_metadata_wrapper('commerce_product', $product);
    $curr_list = $wrapper->field_order_reference->value();

    if (!$curr_list){
        $curr_list = array();
    }

    $curr_list[] = $orderID;
    $wrapper->field_order_reference->set($curr_list);

    $result = $wrapper->save();

  }
}

Answer 1

DOH! - Seconds after adding my previous edit i realised what was wrong. Below the final code :)

function example_rules_action_info() {
  $actions = array();

  $actions['commerce_set_product_order_ref'] = array(
    'label' => t('Link an order to the purchased product'),
    'group' => t('Custom group'),
    'parameter' => array(
      'commerce_line_item' => array(
        'type' => 'commerce_line_item',
        'label' => t('Line item'),
      ),
    ),
  );

  return $actions;
}


function commerce_set_product_order_ref($line_item, $order) {
  if (in_array($line_item->type, commerce_product_line_item_types())) {

    $sku = $line_item->line_item_label;
    $product = commerce_product_load_by_sku($sku);
    $orderID = $line_item->order_id;
    $wrapper = entity_metadata_wrapper('commerce_product', $product);
    $curr_list = $wrapper->field_order_reference->value();
    $new_ref = commerce_order_load($orderID);

    if (!$curr_list){
        $curr_list = array();
    }

    $curr_list[] = $new_ref;
    $wrapper->field_order_reference->set($curr_list);

    $result = $wrapper->save();

  }
}