CakePHP validation on => 'create', on => 'update'

Question

I'm hoping you cakephp experts can answer this re Cake 2.1 and data validation in the model.

Cake gives you an "on" key for use in the validate array. I understand what the docs say about this but my question is, what's the point of these two items.

Let's say I have a validation rule for when a record is created. The validation passes and the record is created.

Then the user goes and edits that record and changes it to something that no longer passes that particular validation. But since I've got my validation set to run on create only, the validation passes and the record is updated with invalid data. It seems to me like this would apply to any on create / on update rules. If a user wanted to bypass validation, just create a valid record, then go and edit it so it's now invalid.

Can someone perhaps help me understand when it might make sense to use on update and on create?

Answer 1

This is most useful in conduction with the required rule. You should set certain fields that are minimally required to be required 'on' => 'create'. This makes the rule fail if those fields don't exist in the data set and the record cannot be created, but allows you to update existing records without having to pass that field each and every time.

For example:

'email' => array(
    'required' => array(
        'on'         => 'create',
        'rule'       => 'notEmpty',
        'message'    => 'Enter your email address',
        'required'   => true,
        'last'       => true
    ),
    'notempty' => array(
        'rule'       => 'notEmpty',
        'message'    => 'Enter your email address',
        'allowEmpty' => false,
        'last'       => true
    ),
    'email' => array(
        'rule'       => 'email',
        'message'    => 'Not a valid email address',
        'last'       => true
    )
)

Answer 2

I found it really useful in cooperation with profile pictures. You need one to be uploaded on create (if it is needed), but on update i can remain empty => no update to picture will be done.