/**
* Prepares an ordering expression
*
* @param DataSetRequestInterface $request
* @param ColumnCollection $columns
*
* @return Expr\OrderBy
*/
protected function getOrderByExpression(DataSetRequestInterface $request, ColumnCollection $columns)
{
$column = $columns->get($request->getOrderBy());
$orderBy = $column->isAggregated() ? $column->getAlias() : $column->getSource();
$orderDir = $request->getOrderDir();
return new Expr\OrderBy($orderBy, $orderDir);
}
