/** {@inheritdoc} */
 public function export(array $data, $sheet)
 {
     $cache = array();
     foreach ($data as $slot => $sheets) {
         foreach ($sheets as $index => $sheetid) {
             $cache[$slot][$index] = $this->sheetIds->getSheetIdName($sheetid);
         }
     }
     $this->_serializeInto($cache, 'visual_slot');
 }
 function findById($id)
 {
     // get sheet name where $id belongs to
     $key = $this->sheetId->getSheetIdName($id);
     // load PackedSheet file
     $ps = $this->load($key);
     if (!empty($ps)) {
         // return sheet record
         return $ps->get($id);
     }
 }