/**
  * Gets name column names of the table associated with the model.
  *
  * @return array   Array of column names
  */
 public function columns()
 {
     $cache =& $this->pixie->orm->column_cache;
     if (!isset($cache[$this->table])) {
         $cache[$this->table] = $this->conn->list_columns($this->table);
     }
     return $cache[$this->table];
 }