private function getAclCollection()
{
if ($this->aclCollection === null) {
try {
$this->aclCollection = $this->getMongoClient()->selectCollection($this->params['databaseName'], 'accesscontrol');
} catch (MongoException $e) {
throw new DatabaseException('Could not select collection', 500, $e);
}
}
return $this->aclCollection;
}