public function single($id): array {
            $return_value = array();
            $temp = array();
            if(is_null($id)) {
                $return_value = [   'success' => 'false',
                                    'message' => 'id field required in GradeRepository::single'];
            }  else {
                $temp = $this->repository->single($id);
                if(is_null($temp['grade'])) {
                    $return_value = [   'success' => 'false',
                                        'message' => 'GradeSingle::single did not return a valid responce'];
                } else {
                    $return_value = [   'success' => 'true',
                                        'message' => 'Grade successfully retreived from database',
                                        'data' => $temp['grade']];
                }
            }
            return $return_value;
        }