public static function getExistingActivities($memberCampaignId, $date, $activityIds = []) {
    $query = \Drupal::entityQuery('openy_campaign_memb_camp_actv')
      ->condition('member_campaign', $memberCampaignId)
      ->condition('date', $date->format('U'));
    if (!empty($activityIds)) {
      $query->condition('activity', $activityIds, 'IN');
    }
    return $query->execute();
  }