code: protected function primaryKeyStringFromArray($dataMember, $opening, $sep = ', ')
      {
          if (empty($this->$dataMember)) {
              return 0;
          }
          $this->query .= $opening;
          $constraintName = 'pk';
          $query = ' PRIMARY KEY (';
          $count = count($this->$dataMember);
          for($i=0; $i<$count; $i++) {
              $item = $this->{$dataMember}[$i];
              $constraintName .= '_'.$item;
              $query .= $item;
              if ($count-1 != $i) {
                  $query .= $sep;
              }
          }
          $query .= ')';
          $this->query .= $constraintName.' '.$query;
      }
docs: For outputting a string of the following form from the 'primaryKeys' array in Database.
  CONSTRAINT pk_id_name PRIMARY KEY (id, name)