protected function subProcess(JoinCapableQuery $query, DBField $field)
 {
     $query->groupBy($field);
 }
 /**
  * @return JoinCapableQuery
  **/
 public function process(Criteria $criteria, JoinCapableQuery $query)
 {
     Assert::isNotNull($this->property);
     return $query->groupBy($criteria->getDao()->guessAtom($this->property, $query));
 }