public function fields($tableAlias = null, $prefixed = false)
{
$columns = '';
/* @var $field Field */
foreach ($this->getIterator()->fields() as $field) {
$columns .= $field->getColumnName($tableAlias, $tableAlias && $prefixed ? $tableAlias . '__' . $field->column->name : null) . ', ';
}
return $columns !== '' ? substr($columns, 0, -2) : '';
}