code: public function load(array $identifier, $rawData, $shardingKey)
      {
          $mappedIdentifier = $this->mapIdentifier($identifier);
          $datas = $this->schemaManager->fetchIds($this->tableName, $mappedIdentifier, array($this->nameField, $this->valueField), $shardingKey);
          $toReturn = array();
          foreach ($datas as $row) {
              $toReturn[$row[$this->nameField]] = $row[$this->valueField];
          }
  
          return $toReturn;
      }
docs: @param array $identifier
  @param bool  $rawData
  @param mixed $shardingKey
  
  @return array