FOS\UserBundle\Model\GroupInterface::getId PHP Method

    function getId();

 /**
  * @param string string         $username
  * @param string GroupInterface $group
  *
  * @return array
  */
 public function findByIncludedUsernameWithoutGroup($username, GroupInterface $group)
 {
     $qb = $this->createQueryBuilder();
     $qb->field('groups.$id')->notEqual(new \MongoId($group->getId()));
     $qb->field('username')->equals(new \MongoRegex('/.*' . $username . '.*/i'));
     return $qb->getQuery()->execute();
 }