drupal_add_library('system', 'ui.sortable');

$( ".survey-questions, .available-questions" ).sortable({
  // We only want to allow dragging with a handle so we specify its class.
  handle : '.li-drag',
  // Specify which items should be draggable.
  // We want all list items except the empty placeholder.
  items: "li:not(.empty)",
  // This little line is what allows us to drag items from one list to another,
  // that's why this class must be set in both views. Without it we would have
  // two useless self reorderable lists. 
  connectWith: ".connect-sortable"

$( ".survey-questions, .available-questions" ).sortable({
  // Show the save button when either one of the lists receive a list item.
  receive : function(event, ui ){
    if ($( "input[name=Save]" ).is(":hidden")) {
      $( "input[name=Save]" ).show();
      $(".message-changes").removeClass('hidden');
    }
  }

$( ".survey-questions" ).sortable({
  // Show the save button when the survey-questions list is reordered.
  update : function(event, ui ){
    if ($( "input[name=Save]" ).is(":hidden")) {
      $( "input[name=Save]" ).show();
      $(".message-changes").removeClass('hidden');
    }
  }
});

<?php
// Stores the relations to be created, updated and deleted.
$relations["insert"] = array();
$relations["update"] = array();
$relations["delete"] = array();

// Parses the form serialization saving it in $temp.
parse_str($questionsSerialized, $temp);
// Stores the questions Ids in an Array
$questionsId = $temp["question"];

// If $questionsId is empty, that means that all the questions where removed.
// Remove all the relations related to the survey
if (empty($questionsId)) {
  // Get the ids of the survey_question relations for the given survey.
  $relations["delete"] = _aw_utils_question_sortable_get_relation_id($relationType, $node->nid);

  if (!empty($relations["delete"])) {
    relation_delete_multiple($relations["delete"]);
  }
}
else {
  // Loop through all the questions checking which ones are to be deleted and to
  // be inserted.
  foreach ($questionsId as $order => $id) {

    // The $id comes in the format questionId-relationId
    // if the question is new the relation won't exist and the $id will only
    // contain the questionId.
    // 
    // Split the id and count the values
    // if 1 - the question is new therefore to be inserted
    // if 2 - the relation already exists so update
    // else throw error
    $splitted = explode("-", $id);
    $splittedLength = count($splitted);

    if ($splittedLength == 1) {
      // Question to insert (relation to create)
      // When we are inserting the array key is the order
      // and the value is the questionId.
      $relations["insert"][$order] = $splitted[0];

    }
    elseif ($splittedLength == 2) {
      // Question to update (relation to update)
      // When we are updating the array key is the new order
      // and the value is the relation id.
      $relations["update"][$order] = $splitted[1];

    }
    else {
      // Malformed id.
      // Throw error.
    }
  }

  // We already have the relations to update and insert
  // now get the existing relations to know which ones to delete
  $existingRelations = _aw_utils_question_sortable_get_relation_id($relationType, $node->nid);

  // We can use the $relations["update"] to check the differences between
  // the submitted and existing relations.
  // Since all the existing relations are always updated, the ones not present
  // in the $relations["update"] are to be deleted.
  $relations["delete"] = array_diff($existingRelations, $relations["update"]);
?>

<? php
// OPERATIONS - insert, update, delete
// Delete
if (!empty($relations["delete"])) {
  relation_delete_multiple($relations["delete"]);
}

// Insert.
foreach ($relations["insert"] as $order => $id) {
  // Specify endpoints.
  $endpoints = array(
    array(
      'entity_type' => $entityType,
      'entity_id' => $nid
    ),
    array(
      'entity_type' => $entityType,
      'entity_id' => $id
    )
  );

  // Creating the relation.
  $relation = relation_create($relationType, $endpoints);
  $relation->field_relation_order[LANGUAGE_NONE][0]['value'] = $order;
  relation_save($relation));

}// End foreach insert.

// Update
foreach ($relations["update"] as $order => $rid) {
  // Load the relation.
  $relation = relation_load($rid);
  $relation->field_relation_order[LANGUAGE_NONE][0]['value'] = $order;
  relation_save($relation));

}// End foreach update.
?>