edit view without modifying file cakePHP

edit view without modifying file cakePHP

View(edit) is displaying all the fields correctly and updating modified
fields but it cant handle files. i.e., if new file is uploaded then it has
to be updated if not old file name has to be retained.
controller:
public function edit($id = null) {
if (!$id) {
throw new NotFoundException(__('Invalid post'));
}
$post = $this->Student->findById($id);
if (!$post) {
throw new NotFoundException(__('Invalid post'));
}
if ($this->request->is('post') || $this->request->is('put')) {
$this->Student->id = $id;
if ($this->Student->save($this->request->data)) {
$this->Session->setFlash(__('Your post has been updated.'));
return $this->redirect(array('action' => 'index'));
}
$this->Session->setFlash(__('Unable to update your post.'));
}
if (!$this->request->data) {
$this->request->data = $post;
}
}
View:
<h1>Edit student record</h1>
<?php
echo $this->Form->create('Student',array('type'=>'file'));
echo $this->Form->input('first_name');
echo $this->Form->input('current_address');
echo 'resume'.$this->Form->file('resume');
echo $this->Form->input ('comments');
echo 'photo'.$this->Form->file('photo');
echo $this->Form->input('id', array('type' => 'hidden'));
//echo $this->Form->input('resume', array('type' => 'hidden'));
//echo $this->Form->input('photo', array('type' => 'hidden'));
echo $this->Form->end('Save Post');
Can someone suggest me how to handle the upload thing