Drupal 7 AJAX Forms

Using AJAX to update a Drupal 7 form could be easier. The documentation on this feature is extremely verbose, and I had a difficult time piecing together a working example. So, here’s the code to modify the values of a second field when the value of the first is selected. The code below will use the taxonomy_voc drop down to control the product model drop down values. This code does not work with field widgets that define their own AJAX.

Wrap the field that’s being controlled and add the callback and wrapper to the controller field.

Thanks to Anne Sturdivant for her assistance in writing this code.

 *  Implements of hook_form_alter() to update a field via AJAX.

function hitachi_module_form_alter(&$form, &$form_state, $form_id) {
  switch ($form_id) {
    case 'contact_us_entityform_edit_form':

    // Wrap the field that being controlled
    // Add the callback and wrapper to the controller field

    // Create a wrapper for the AJAX callback to populate the model
    $form['field_product_model']['#prefix'] = '<div id="hitachi_wrapper_type">';
    $form['field_product_model']['#suffix'] = '</div>';

    // If we are editing an existing form, we already have the values
    if (!empty($form['taxonomy_voc'][LANGUAGE_NONE]['#default_value']) 
        || isset($form_state['values']['taxonomy_voc'][LANGUAGE_NONE][0])) {
      $form['field_product_model'] = _hitachi_set_model($form, $form_state);

    // Create an AJAX callback. This is the magic bit that does all the AJAX.
    $form['taxonomy_voc'][LANGUAGE_NONE]['#ajax'] = array(
      'callback' => '_hitachi_set_model', //Must match the function name below
      'wrapper' => 'hitachi_wrapper_type',

 * AJAX callback to grab all the nodes with a given term.
function _hitachi_set_model($form, $form_state) {
  if (!isset($form['#after_build_done']) && isset($form_state['triggering_element'])) {
    $product_types = array_keys($form_state['triggering_element']['#value']);

    // Populate all the product models with all the product titles from that division.
    foreach($product_types as $product_type) {
      $entities = _hitachi_module_get_nodes_from_tid($product_type);
      $nodes = node_load_multiple(array_keys($entities['node']));
      foreach($nodes as $node) {
        $title = entity_metadata_wrapper('node', $node)->title->value();
        $key = preg_replace('/[^a-z]/i','', strtolower($title));
        $form['field_product_model'][LANGUAGE_NONE]['#options'][$key] = $title;

  return $form['field_product_model'];