private function getGroupKeyForModel(Model $model)
    {
        $key = "";

        foreach ($this->groups as $group) {
            $key .= $model[$group] . "|";
        }

        return $key;
    }
private function getGroupKeyForModel(Model $model)
    {
        $key = "";

        foreach ($this->groups as $group) {
            $key .= $model[$group] . "|";
        }

        return $key;
    }
private function getGroupKeyForModel ( Model $ model ) { $ key = "" ; foreach ( $ this -> groups as $ group ) { $ key .= $ model [ $ group ] . "|" ; } return $ key ; }
Returns a string which uniquely represents the group the given model should be in for aggregation.
@param Model $model
@return string
Returns a string which uniquely represents the group the given model should be in for aggregation .