Manager/GenericDocumentManager.php
public function findOneBy($filters = [], $sort = null)
    {
        return $this->dm->getRepository($this->document)->findOneBy($filters, $sort);
    }
public function findOneBy($filters = [], $sort = null)
    {
        return $this->dm->getRepository($this->document)->findOneBy($filters, $sort);
    }
FindOnBy

@param array $filters List or conditional selectors http://bit.ly/1efirww

@return MongoCursor