CakePHP: pass product_id value to checkout add page - cakephp

Question

I'm pretty new to cakePHP and I've been stuck on this problem for a few days now. My Products index view displays a list of products we have in inventory and includes a "Checkout" action with every product that points to the Checkout/add view. The problem is the product_id from the product that needs to be checked out does not get passed to the add checkout page and I can't figure out how to make this happen. If anyone has any suggestions I could really use some help.
Here is my CheckoutController add action:
public function add() {
if ($this->request->is('post')) {
$this->Checkout->create();
if ($this->Checkout->save($this->request->data)) {
$this->Session->setFlash(__('The checkout has been saved'));
$this->redirect(array('action' => 'index'));
} else {
$this->Session->setFlash(__('The checkout could not be saved. Please, try again.'));
}
}
$products = $this->Checkout->Product->find('list');
$users = $this->Checkout->User->find('list');
$this->set(compact('products', 'users'));
}
Checkout Add View
<?php echo $this->Form->create('Checkout');?>
<fieldset>
<legend><?php echo __('Add Checkout'); ?></legend>
<?php
echo $this->Form->input('product_id');
echo $this->Form->input('start_time');
echo $this->Form->input('end_time');
echo $this->Form->input('user_id');
echo $this->Form->input('description');
?>
</fieldset>
Link from the Products index page
<?php echo $this->Html->link(__('Checkout'), array('controller' => 'Checkouts','action' => 'add', $product['Product']['id'])); ?>

Answer 1

Cake will pass the product_id as the first argument of your action; Default Cake 'Routes' will match this url;
/mycontroller/myaction/param1/param2/param3
To this action:
MycontrollerController::myaction(param1, param2, param3)
You can pass this value to the form by adding an argument to the add() action and adding it to the 'request' if the form is not posted. Like this;
public function add($productId = null) {
if ($this->request->is('post')) {
$this->Checkout->create();
if ($this->Checkout->save($this->request->data)) {
$this->Session->setFlash(__('The checkout has been saved'));
$this->redirect(array('action' => 'index'));
} else {
$this->Session->setFlash(__('The checkout could not be saved. Please, try again.'));
}
} else {
$this->request->data['Checkout']['product_id'] = $productId;
}
$products = $this->Checkout->Product->find('list');
$users = $this->Checkout->User->find('list');
$this->set(compact('products', 'users'));
}
This will automatically propagate the 'value' of the product_id drop down

Answer 2

from your links on the products index page it seems that
public function add()
should read
public function add($product_id)
furthermore you should set the $product_id into the view, and also
fill it into the inputbox echo $this->Form->input('product_id', array('value'=>$product_id));