trait SearchApiHandlerTrait in Search API 8

trait SearchApiHandlerTrait {

  /**
   * Overrides the Views handlers' ensureMyTable() method.
   *
   * This is done since adding a table to a Search API query is neither
   * necessary nor possible, but we still want to stay as compatible as possible
   * to the default SQL query plugin.
   */
  public function ensureMyTable() {
  }

  /**
   * Determines the entity type used by this handler.
   *
   * If this handler uses a relationship, the base class of the relationship is
   * taken into account.
   *
   * @return string
   *   The machine name of the entity type.
   *
   * @see \Drupal\views\Plugin\views\HandlerBase::getEntityType()
   */
  public function getEntityType() {
    return $this->definition['entity_type'] ?? parent::getEntityType();
  }

  /**
   * Returns the active search index.
   *
   * @return \Drupal\search_api\IndexInterface|null
   *   The search index to use with this filter, or NULL if none could be
   *   loaded.
   */
  protected function getIndex() {
    if ($this
      ->getQuery()) {
      return $this
        ->getQuery()
        ->getIndex();
    }
    $base_table = $this->view->storage
      ->get('base_table');
    return SearchApiQuery::getIndexFromTable($base_table);
  }

  /**
   * Retrieves the query plugin.
   *
   * @return \Drupal\search_api\Plugin\views\query\SearchApiQuery|null
   *   The query plugin, or NULL if there is no query or it is no Search API
   *   query.
   */
  public function getQuery() {
    $query = $this->query ?? $this->view->query ?? NULL;
    return $query instanceof SearchApiQuery ? $query : NULL;
  }

}