abstract class TaxonomyFormatterBase

LinkFormatter.php in drupal/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/LinkFormatter.php

Contains \Drupal\taxonomy\Plugin\field\formatter\LinkFormatter.

PlainFormatter.php in drupal/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/PlainFormatter.php

Contains \Drupal\taxonomy\Plugin\field\formatter\PlainFormatter.

RSSCategoryFormatter.php in drupal/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/RSSCategoryFormatter.php

Contains \Drupal\taxonomy\Plugin\field\formatter\RSSCategoryFormatter.

abstract class TaxonomyFormatterBase extends FormatterBase {

  /**
   * Implements \Drupal\field\Plugin\Type\Formatter\FormatterInterface::prepareView().
   *
   * This preloads all taxonomy terms for multiple loaded objects at once and
   * unsets values for invalid terms that do not exist.
   */
  public function prepareView(array $entities, $langcode, array &$items) {
    $tids = array();

    // Collect every possible term attached to any of the fieldable entities.
    foreach ($entities as $id => $entity) {
      foreach ($items[$id] as $delta => $item) {

        // Force the array key to prevent duplicates.
        if ($item['tid'] !== 0) {
          $tids[$item['tid']] = $item['tid'];
        }
      }
    }
    if ($tids) {
      $terms = taxonomy_term_load_multiple($tids);

      // Iterate through the fieldable entities again to attach the loaded term
      // data.
      foreach ($entities as $id => $entity) {
        $rekey = FALSE;
        foreach ($items[$id] as $delta => $item) {

          // Check whether the taxonomy term field instance value could be
          // loaded.
          if (isset($terms[$item['tid']])) {

            // Replace the instance value with the term data.
            $items[$id][$delta]['entity'] = $terms[$item['tid']];
          }
          elseif ($item['tid'] === 0 && isset($item['entity'])) {

            // Leave the item in place.
          }
          else {
            unset($items[$id][$delta]);
            $rekey = TRUE;
          }
        }
        if ($rekey) {

          // Rekey the items array.
          $items[$id] = array_values($items[$id]);
        }
      }
    }
  }

}