Drupal 9 - Working with Taxonomy Entities

load_select_options.php

<?php

// Util functions to load a select lists options from a taxonomy or a node field with a text list.

function build_form() {
  $form = [];
  
  // Load a two level deep select tree from a taxonomy
  $options = load_taxonomy_as_select_options('example_taxonomy');
  $form['select_tree'] = [
    '#type' => 'select',
    '#title' => $this->t('Taxonomy Tree Select'),
    '#options' => $options,
    '#size' => 1,
  ];  

  // Load a thes select options from a node text list field.
  $options = load_node_field_options_as_select_options('news_artical', 'artical_type_field');
  $form['select_field'] = [
    '#type' => 'select',
    '#title' => $this->t('Field Select Options'),
    '#options' => $options,
    '#size' => 1,
  ];  

}

function load_taxonomy_as_select_options($vid, $required = FALSE) {
  // We only support two levels
  $taxonomy_tree = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadTree($vid, 0, 2);
  $options = [];
  $current_element = &$options;
  if (!$required) {
    $options['All'] = t('- Any -');
  }
  foreach ($taxonomy_tree as $key => $term) {
    if ($term->depth == 0) {
      $options[$term->name] = [];
      $current_element = &$options[$term->name];
    }
    else {
      $current_element[$term->tid] = $term->name;
    }
  }
  return $options;
}

function load_node_field_options_as_select_options($node_name, $field_name, $required = FALSE) {
  $options = [];
  if (!$required) {
    $options['All'] = t('- Any -');
  }

  $field_definitions = \Drupal::service('entity_field.manager')->getFieldDefinitions('node', $node_name);
  if (isset($field_definitions[$field_name])) {
    $options += options_allowed_values($field_definitions[$field_name]->getFieldStorageDefinition());
  }
  return $options;
}

taxonomyFunctions.php

<?php

// Commonly used functions and code snippets.

// Get the vocabulary ID.
    $vocabularies = taxonomy_vocabulary_get_names(); // Deprecated
    $vocabularies = \Drupal::entityQuery('taxonomy_vocabulary')->execute(); // use this
    $vid = array_search($taxonomy_name, 'tags');
    echo $vid   // output: tags

// Set a single value taxonomy reference field.
      $entity->set('field_taxonomy_term_ref', 3);
      
// Set multiple values taxonomy reference field.
      $entity->set('field_taxonomy_term_ref', [3,4,7]);
      
// Clear a  taxonomy reference field.  
      $entity->set('field_taxonomy_term_ref', NULL);

// Load a term using its ID.
/** @var \Drupal\taxonomy\Entity\Term $term */
$term = \Drupal\taxonomy\Entity\Term::load($term_id)

// Load a term using its name.
$terms = \Drupal::entityTypeManager()->getStorage('taxonomy_term')
  ->loadByProperties(['name' => $term_name, 'vid' => 'tags']);

// Using Entity query.
    $query = \Drupal::entityQuery('taxonomy_term');
    $query->condition('vid', "tags");
    $query->condition('name', $term_name);
    $tids = $query->execute();
  

// Load a term using a custom field.
$terms = \Drupal::entityTypeManager()->getStorage('taxonomy_term')
  ->loadByProperties(['field_custom_name' => 'internal-id-12345', 'vid' => 'my_special_terms']);

// Make sure only one
    if (count($terms) == 1) {
      /** @var  \Drupal\taxonomy\Entity\Term $term */
      $term = array_pop($terms);
    }    

// Cycle
      foreach ($terms as $term) {
        $term_id = $term->id();
        $term_name = $term->getName();
      }


// Nested refrences

  // Does the node have a taxonomy term reference
  if ($node->hasField('field_my_taxonomy_ref') && (!$node->get("field_my_taxonomy_ref")->isEmpty())) {
      $term_id = $node->field_my_taxonomy_ref->target_id;      
      // This check should not be needed as we already checked it is not empty.
      if (isset($term_id)) {
          
          // Load the term and get details
          $term = \Drupal\taxonomy\Entity\Term::load($term_id);
          $term_name = $term->name->value;
          
          // If the term has a taxonomy term reference itself.
          $another_term_tid = $term->field_another_taxonomy_ref->target_id;
          $another_term = \Drupal\taxonomy\Entity\Term::load($another_term_tid);
          $another_term_name = $another_term->name->value;
      }
  }
          
      
  }



//********** Get Term data. ***********//

  /** @var \Drupal\taxonomy\Entity\Term $term */
  $term = \Drupal\taxonomy\Entity\Term::load($tid);

  // Get the name & description
  $term_name = $term->getName();
  $term_description = $term->getDescription())

  // get the bundle name / VID
  $bundle_name = $term->bundle();
  
  // Get a field value (array)
  $my_field = $term->field_my_field->getValue();
  // Get as a single value.
  $my_field = $term->field_my_field->value;


//********** Create ***********//
  $term_data = [
    'vid' => 'vocabulary',
    'name' => 'tag name',
  ];
  $term = \Drupal\taxonomy\Entity\Term::create($term_data);
  $term->save();

// more options from https://www.drupal8.ovh/en/tutoriels/55/create-taxonomy-term-programmatically-on-drupal-8
  $term_data = [
          'vid' => 'test_vocabulary',
          'langcode' => 'en',
          'name' => 'My tag',
          'description' => [
            'value' => '<p>My description.</p>',
            'format' => 'full_html',
          ],
          'weight' => -1,
          'parent' => array(0),
    ]);



    // Create the taxonomy.
    $attribute_machine_name = "new_vocabulary";
    $vocabularies = \Drupal\taxonomy\Entity\Vocabulary::loadMultiple();
    if (!isset($vocabularies[$attribute_machine_name])) {
      $vocabulary = \Drupal\taxonomy\Entity\Vocabulary::create(array(
        'vid' => $attribute_machine_name,
        'description' => "a test Vocabulary",
        'name' => "New Vocabulary",
      ));
      $vocabulary->save();
    }


//********** Translations. ***********//

   // Load a term in multiple languages.
      $en_term = \Drupal::service('entity.repository')->getTranslationFromContext($term, 'en');
      $fr_term = \Drupal::service('entity.repository')->getTranslationFromContext($term, 'fr');
      $de_term = \Drupal::service('entity.repository')->getTranslationFromContext($term, 'de');

    // Load a term for the current language.
      $language =  \Drupal::languageManager()->getCurrentLanguage()->getId();
      $term = \Drupal::service('entity.repository')->getTranslationFromContext($term, $language);

    // Load for the current language 
    $terms = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadByProperties(['vid' => $taxonomy_name]);
    $language = \Drupal::languageManager()->getCurrentLanguage()->getId();
    foreach ($terms as $key => $term) {
      $terms[$key] = \Drupal::service('entity.repository')->getTranslationFromContext($term, $language);
    }