cakePHP optional validation for file upload - validation

Question

How to make file uploading as optional with validation?
The code below validates even if i didn't selected any file.
I want to check the extension only if i selected the the file.
If i am not selecting any file it should not return any validation error.
class Catalog extends AppModel{
var $name = 'Catalog';
var $validate = array(
'name' => array(
'rule' => '/^[a-z0-9 ]{0,}$/i',
'allowEmpty' => false,
'message' => 'Invalid Catalog name'
),
'imageupload' => array(
'rule' => array('extension',array('jpeg','jpg','png','gif')),
'required' => false,
'allowEmpty' => true,
'message' => 'Invalid file'
),
);
}
thanks in advance

Answer 1

"I assign $this->data['Catalog']['image'] = $this->data['Catalog']['imageupload']['name'];"
So by the time you save your data array, it looks something like this I assume:
array(
'image' => 'foobar',
'imageupload' => array(
'name' => 'foobar',
'size' => 1234567,
'error' => 0,
...
)
)
Which means, the imageupload validation rule is trying to work on this data:
array(
'name' => 'foobar',
'size' => 1234567,
'error' => 0,
...
)
I.e. the value it's trying to validate is an array of stuff, not just a string. And that is unlikely to pass the specified validation rule. It's also probably never "empty".
Either you create a custom validation rule that can handle this array, or you need to do some more processing in the controller before you try to validate it.

Answer 2

Concept:
In Controller, before validating, or saving (which does validation automatically by default) check if any file is uploaded. If not uploaded, then unset validator for the file field.
Sample code:
Controller
// is any image uploaded?
$isNoFileUploaded = ($this->request->data['Model']['field_name']['error'] == UPLOAD_ERR_NO_FILE) ? true : false ;
if ($isNoFileUploaded) {
$this->Model->validator()->remove('field_name');
}
Notes:
This solution comes under preprocessing as one of the two alternative approaches (preprocessing in controller, custom validation in model) suggested by #deceze's answer