File uploads

Enable multipart encoding before binding, then render a file input. Here the controller supplies the $article being edited.

templates/Articles/edit.php

<?php
$form = $this->Form
    ->form($article)
    ->multipart()
    ->bind();
?>
<?= $form->open() ?>
<?= $form->control('attachment')
    ->type('file')
    ->label('PDF attachment')
    ->attributes(['accept' => 'application/pdf']) ?>
<?= $form->submit('Upload') ?>
<?= $form->close() ?>

multipart() sets the encoding needed to send files. It keeps the form's HTTP method, including the method override used when editing an existing entity. Rendering a file input without multipart encoding throws an exception.

The browser's accept attribute helps users choose a file; validate uploads in your application. Read the upload through CakePHP's $this->request->getUploadedFile('attachment'), then apply your existing storage and persistence workflow.

Accept several files

Replace the attachment control with:

echo $form->control('attachments')
    ->type('file')
    ->multiple()
    ->attributes(['accept' => 'application/pdf']);

This submits attachments[]. The uploaded files are available under $this->request->getUploadedFiles()['attachments'].

File inputs never pre-fill from existing values. Show an existing attachment's name or download link separately from the upload control.