DownloadsController.php

<?php

namespace app\controllers;
use app\models\Downloads;

class DownloadsController extends \lithium\action\Controller {

    public function index() {

        $this->request->privateKeys = array('id', 'user_id');

        // Dynamic conditions
        $conditions = array(...);

        $downloads = Downloads::find('all', array(
            'fields' => array('user_id', 'Surveys.name'),
            'conditions' => $conditions,
            'with' => 'Surveys',
            'order' => array('created' => 'desc')
        ));

        return compact('downloads');
    }

}
?>

media.php

<?php
// config/bootstrap/media.php

use lithium\util\Set;
use lithium\net\http\Media;

// Note: I did not need the "privateKeys" functionality so it has been removed.

Media::type('csv', 'application/csv', array(
    'encode' => function($data, $handler, $response) {
        // Assume first key is the one we are dumping
        $data = reset($data);

        // Write
        ob_start();

        $out = fopen('php://output', 'w');
        foreach ($data as $record) {
            $record = Set::flatten($record);
            if (!isset($headers)) {
                $headers = array_keys($record);
                fputcsv($out, $headers);
            }
            fputcsv($out, $record);
        }
        fclose($out);
        return ob_get_clean();
    }
));