1. drupal
    1. 5

This is an example outlining how a module can be used to extend existing content types.

We will add the ability for each node to have a "rating," which will be a number from one to five.

Functions & methods

nodeapi_example_form_alterImplementation of hook_form_alter().
nodeapi_example_nodeapiImplementation of hook_nodeapi().
theme_nodeapi_example_ratingA custom theme function.
View source

 * @file
 * This is an example outlining how a module can be used to extend existing
 * content types.
 * We will add the ability for each node to have a "rating," which will be a
 * number from one to five.

 * Implementation of hook_form_alter().
 * By implementing this hook, we're able to modify any form. We'll only make
 * changes to two types: a node's content type configuration and edit forms.
function nodeapi_example_form_alter($form_id, &$form) {
  // We're only modifying node forms, if the type field isn't set we don't need
  // to bother; otherwise, store it for later retrieval.
  if (isset($form['type'])) {
    $type = $form['type']['#value'];
  elseif (isset($form['orig_type'])) {
    $type = $form['orig_type']['#value'];
  else {

  // The rating is enabled on a per node type basis. The variable used to store
  // this information is named named using both the name of this module, to
  // avoid namespace conflicts, and the node type, because we support multiple node
  // types.
  $enabled = variable_get('nodeapi_example_'. $type, 0);

  switch ($form_id) {
    // We need to have a way for administrators to indicate which content
    // types should have our rating field added. This is done by inserting a
    // checkbox in the node's content type configuration page. The variable will
    // be automatically saved by the settings form.
    case 'node_type_form':
      $form['workflow']['nodeapi_example_'. $type] = array(
        '#type' => 'radios',
        '#title' => t('NodeAPI Example Rating'),
        '#default_value' => $enabled,
        '#options' => array(0 => t('Disabled'), 1 => t('Enabled')),
        '#description' => t('Should this node have a rating attached to it?'),
    case $type .'_node_form':
      // If the rating is enabled for this node type, we insert our control
      // into the form.
      if ($enabled) {
        $options = array(0 => t('Unrated'), 1, 2, 3, 4, 5);
        $form['nodeapi_example_rating'] = array(
          '#type' => 'select',
          '#title' => t('Rating'),
          '#default_value' => $form['#node']->nodeapi_example_rating,
          '#options' => $options,
          '#required' => TRUE,
          '#weight' => 0,

 * Implementation of hook_nodeapi().
 * We will implement several node API operations here. This hook allows us to
 * act on all major node operations, so we can manage our additional data
 * appropriately.
function nodeapi_example_nodeapi(&$node, $op, $teaser, $page) {
  switch ($op) {
    // When the content editing form is submitted, we need to validate the input
    // to make sure the user made a selection, since we are requiring the rating
    // field. We have to check that the value has been set to avoid showing an
    // error message when a new blank form is presented. Calling form_set_error()
    // when the field is set but zero ensures not only that an error message is
    // presented, but also that the user must correct the error before being able
    // to submit the node.
    case 'validate':
      if (variable_get('nodeapi_example_'. $node->type, TRUE)) {
        if (isset($node->nodeapi_example_rating) && !$node->nodeapi_example_rating) {
          form_set_error('nodeapi_example_rating', t('You must rate this content.'));

    // Now we need to take care of loading one of the extended nodes from the
    // database. An array containing our extra field needs to be returned.
    case 'load':
      $object = db_fetch_object(db_query('SELECT rating FROM {nodeapi_example} WHERE nid = %d', $node->nid));
      return array('nodeapi_example_rating' => $object->rating);

    // Insert is called after the node has been validated and saved to the
    // database. It gives us a chance to create our own record in the database.
    case 'insert':
      db_query('INSERT INTO {nodeapi_example} (nid, rating) VALUES (%d, %d)', $node->nid, $node->nodeapi_example_rating);

    // Update is called when an existing node has been changed. Here, we use a
    // DELETE then an INSERT rather than an UPDATE. The reason is that a node
    // created before this module was installed won't already have a rating
    // saved so there would be nothing to update.
    case 'update':
      db_query('DELETE FROM {nodeapi_example} WHERE nid = %d', $node->nid);
      db_query('INSERT INTO {nodeapi_example} (nid, rating) VALUES (%d, %d)', $node->nid, $node->nodeapi_example_rating);

    // Delete is called whn the node is being deleted, it gives us a chance
    // to delete the rating too.
    case 'delete':
      db_query('DELETE FROM {nodeapi_example} WHERE nid = %d', $node->nid);

    // Finally, we need to take care of displaying our rating when the node is
    // viewed. This operation is called after the node has already been prepared
    // into HTML and filtered as necessary, so we know we are dealing with an
    // HTML teaser and body. We will inject our additional information at the front
    // of the node copy.
    // Using nodeapi('view') is more appropriate than using a filter here, because
    // filters transform user-supplied content, whereas we are extending it with
    // additional information.
    case 'view':
      $node->content['nodeapi_example'] = array(
        '#value' => theme('nodeapi_example_rating', $node->nodeapi_example_rating),
        '#weight' => -1,

 * A custom theme function.
 * By using this function to format our rating, themes can override this presentation
 * if they wish; for example, they could provide a star graphic for the rating. We
 * also wrap the default presentation in a CSS class that is prefixed by the module
 * name. This way, style sheets can modify the output without requiring theme code.
function theme_nodeapi_example_rating($rating) {
  $output = '<div class="nodeapi_example_rating">';
  $options = array(
    0 => t('Unrated'),
    1 => t('Poor'),
    2 => t('Needs improvement'),
    3 => t('Acceptable'),
    4 => t('Good'),
    5 => t('Excellent'));
  $output .= t('Rating: %rating', array('%rating' => $options[(int)$rating]));
  $output .= '</div>';
  return $output;