DataMapper ORM v1.8.0

[eluser]ricardocasares[/eluser]
Hi guys, I'm struggling to set up the validation rules to validate the related items on a specific object, ie: A user can have no more than 3 products related to it.

I believe DataMapper can check for this validation using _related_max_size rule in Related validation, but I can't figure out how to use it on the $validation array in the model.

So far I've tried this in both my user and product models:

Code:

var $validation = array(
    'product' => array(
         'rules' => array('max_size' => 3)
    )
);

Can somebody show me an example on how to set up this at the model, controller and finally the view (specificly how to show the errors for this)?

Edit: What I mean is, a user has many products, and can create a certain amount of them, let's say 3 products, when that amount is reached, the user can no longer create products, and this validation rule should not permit the user to create more products.

This would be the DB Schema:

Code:

Users table
------------------
id   |  username  |
------------------

Code:

Products table
------------------------
id  | user_id |  name   |
------------------------

Thanks!