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I wrote module with hook_form_alter to modify node_forum_form, i.e., node/add/forum form. One forum field is a taxonomy entity reference, field_topic. I want to set the field_topic selection based on the value from a specific node (NID=77) of type current_topic, which also has field_topic as an entity ref.

field_topic is ref to Topic taxonomy.

After loading node 77, I got the TID of the current_topic field_topic, loaded the term, and then got the term name. Name is displayed on the form above the title using $form['title']['#markup'].

Problem: Before returning the form, how can I set the form default selection to be that same field_topic value?

use Drupal\taxonomy\Entity\Term;
use Drupal\Core\Form\FormStateInterface;

function MYMODULE_form_alter(&$form, FormStateInterface $form_state, $form_id) {

  if ($form_id != 'node_forum_form') {
    return FALSE;
  }
  else {
    $nid = 77;
    $node = \Drupal::entityTypeManager()->getStorage('node')->load($nid);

    $current_topic_id = $node->get('field_topic')->getString(); //get the TID
    $term = Term::load($current_topic_id);
    $the_topic = $term->getName();

    $form['title']['#markup'] = t('<h3>The Current Topic is:  <i>' . $the_topic . '</i></h3>');

    // REPLACE THE NEXT LINE WITH CODE TO SET THE CURRENT TOPIC
    $form['field_topic']['widget']['#options']['_none'] = 'Click & Select the Current Topic';

    return $form;
  }
}
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I suppose with

set the form selection

you mean the default value of the taxonomy term reference field?

If yes, in the code above try this:

$form['field_topic']['widget']['#default_value'] = $term->tid();

Btw. you also want to change your implementation from MYMODULE_form_alter to MYMODULE_form_node_forum_form_alter, because the former hook will be called for all forms, whereas the latter is just called when the forum node form renders.

  • Thanks for your suggestion. With a small change it worked perfectly! $form['field_topic']['widget']['#default_value'] = $current_topic_id; – dkrockville Oct 8 '18 at 18:22
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The $term->tid() was calculated earlier in the code. That was the solution.

  • While this all works perfectly for admin users, authenticated users see only '- Select a value -' as the default value. I verified with set_message that the code knows the correct default value of the taxonomy term. What could be causing this? – dkrockville Nov 8 '18 at 1:36
  • Note in case of authenticated user, <option value="_none"> is the only item in the select list. For admin user, the select list contains all of the taxonomy items with the correct option value set to selected="selected". – dkrockville Nov 8 '18 at 1:54

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