Passing field value to #autocomplete_route_name in custom form

Question

I am creating a custom form where I have 2 fields.

1. Taxonomy : select field having list of vocabularies.
2. Terms : Autocomplete field having terms list.

When I start typing in terms field, the value of the term field is passed to the routing function. However I also need the value of the taxonomy field in routing function so that I can restrict the terms list.

Is there anyway that I can get the other field values in the routing function?

Here is my buildform function :

public function buildForm(array $form, FormStateInterface $form_state) {
  $form['taxonomy'] = [
    '#type' => 'select',
    '#title' => $this->t('Select Taxonomy'),
    '#options' => $taxonomies,
  ];

  $form['taxonomy_terms'] = [
    '#type' => 'textfield',
    '#autocomplete_route_name' => 'unido_drupal_admin.get_taxonomies'
  ];

  return $form;
}

Here is my routing function :

public function get_taxonomies(Request $request) {
  // Here I need to get taxonomy field value to restrict the result.
  $params = $request->query->all();
  $result = \Drupal\taxonomy\Entity\Vocabulary::loadMultiple();
}

Thanks.

Answer 1

You need to define #autocomplete_route_parameters. I'm not sure if the form gets rebuilt during autocomplete queries (most likely not!) so you might need to define a #ajax on the vocabulary selector in order to rebuild the form and return the taxonomy_terms field with correct parameters set. This way you're defining a clear dependency, that field 2's available values depend on field 1's value. Below code is untested, but hopefully pushed you in the right direction:

public function buildForm(array $form, FormStateInterface $form_state) {
  $form['taxonomy'] = [
    '#type' => 'select',
    '#title' => $this->t('Select Taxonomy'),
    '#options' => $taxonomies,
    '#ajax' => [
      'callback' => 'Namespace\To\Your\Entity::vocabulary_callback',
      'event' => 'change',
      'wrapper' => 'term-wrapper'
    ],
  ];

  // Initially return a disabled field.
  $form['taxonomy_terms'] = [
    '#type' => 'textfield',
    '#disabled' => TRUE,
    '#prefix' => '<div id="term-wrapper">',
    '#suffix' => '</div>',
  ];

  // If someone's chosen a vocabulary, rewrite the field.
  if ($vid = $form_state->getValue('taxonomy', false)) {
    $form['taxonomy_terms'] = [
      '#type' => 'textfield',
      '#prefix' => '<div id="term-wrapper">',
      '#suffix' => '</div>',
      '#autocomplete_route_name' => 'unido_drupal_admin.get_taxonomies',
      '#autocomplete_route_parameters' => ['vid' => $vid],
    ];
  }

  return $form;
}

public function vocabulary_callback(array &$form, FormStateInterface $form_state) {
  return $form['taxonomy_terms'];
}

You also need to define this as a route parameter in your route's path element:

unido_drupal_admin.get_taxonomies:
  path: '/path/to/your/autocomplete/{vid}'

And also accept the parameter in your autocomplete function:

public function get_taxonomies(Request $request, $vid) {

There might be better ways to do this though, but with my limited D8 knowledge, this is how I'd approach it.