public static function deleteWinners($campaignId, $isAll = TRUE) {
    $connection = \Drupal::service('database');
    /** @var \Drupal\Core\Database\Query\Select $query */
    $query = $connection->select('openy_campaign_winner', 'w');
    $query->fields('w', ['id']);
    $query->join('openy_campaign_member_campaign', 'mc', 'w.member_campaign = mc.id');

    // Delete only winners with defined activity.
    if (!$isAll) {
      $query->condition('w.activity', 0, '!=');
    }
    $query->condition('mc.campaign', $campaignId);

    $winnerIDs = $query->execute()->fetchCol();

    /** @var \Drupal\Core\Entity\EntityStorageInterface $storage */
    $storage = \Drupal::service('entity_type.manager')->getStorage('openy_campaign_winner');
    $winners = $storage->loadMultiple($winnerIDs);
    $storage->delete($winners);
  }