/**
  * Sort by lookup table
  *
  * @param QueryBuilder $QB
  * @param string $tablealias
  * @param string $colname
  * @param string $order
  */
 public function sort(QueryBuilder $QB, $tablealias, $colname, $order)
 {
     if (!$this->usesLookup()) {
         parent::sort($QB, $tablealias, $colname, $order);
         return;
     }
     $schema = 'data_' . $this->schema->getTable();
     $field = $this->column->getColName();
     $rightalias = $QB->generateTableAlias();
     $QB->addLeftJoin($tablealias, $schema, $rightalias, "{$tablealias}.{$colname} = {$rightalias}.pid");
     $this->column->getType()->sort($QB, $rightalias, $field, $order);
 }