export.php

<?php

        $data = $this->Table->find()->all();
        $file = new \SplFileObject(TMP . "my_export.csv", 'w');
        $title = function ($row) use ($file) {
            static $done = false;
            if (!$done) {
                $file->fputcsv(array_keys($row));
                $done = true;
            }
            return $row;
        };

        $data
            ->map($title)
            ->each(function ($row) use ($file) {
                 $file->fputcsv($row);
            });