public function getComputedColumns()
    {
        //make sure we only run this once and then return the cached version
        if (empty($this->computedColumns)) {
            foreach ($this->getColumns() as $column) {
                if (!$column->getOption('is_related') && $column->getOption('is_computed')) {
                    $this->computedColumns[$column->getOption('column_name')] = $column->getOption('column_name');
                }
            }
        }

        return $this->computedColumns;
    }