Magento – Magento set Cookie

First, security:

This pattern is extremely dangerous:

$cookieVal = Mage::app()->getRequest()->getParam('source');
$theCookie = $model->set($cookieName, $cookieVal);

You should never accept user input and shove to a cookie - it gives a would-be attacker the instant ability to set any cookie they want from your domain.

Secondly, cookies:

[Insert "How do they work" meme here]

Cookies are sent back to a user session with the Response object. If you try to set a cookie after the header of the response you'll likely get this warning in the system.log or the general PHP log:

Cannot modify header information - headers already sent by //...

The only place you should be setting cookies is from within a controller action and before it loads the layout. If you're attempting to set cookies from anywhere else in the application you may have unexpected results.

Finally, your real issue:

Okay, so enough browbeating.

getParam is a method returned from Zend_Controller_Request_Http and does a series of tests:

public function getParam($key, $default = null)
{
    $keyName = (null !== ($alias = $this->getAlias($key))) ? $alias : $key;

    $paramSources = $this->getParamSources();
    if (isset($this->_params[$keyName])) {
        return $this->_params[$keyName];
    } elseif (in_array('_GET', $paramSources) && (isset($_GET[$keyName]))) {
        return $_GET[$keyName];
    } elseif (in_array('_POST', $paramSources) && (isset($_POST[$keyName]))) {
        return $_POST[$keyName];
    }

    return $default;
}

As you can see, the $default return value is null but you can change this with the second parameter. Try testing your return value. If it's null, pass a second parameter to getParam.

Alternatively, use of getParams (plural) will return all set parameters in the current request, regardless of the set method - e.g. GET or POST. Try doing a var_dump of getParams to test if your value is set.

I would also advise against using Mage::app()->getRequest() if you are within the scope of a controller action - instead use $this->getRequest().

Edit:

As @vinai pointed out in your other question, var_dump and echo push content to the browser and thus preclude your ability to set cookies.

To save prices per website/store and to avoid getting the 'url_key' error do the following:

foreach ($storeIds as $storeId) {
    //load the product with store id
    $product = Mage::getModel('catalog/product')
        ->setStoreId($storeId)
        ->load($productId);

    //Set the store price
    $product->setPrice($price);

    //To stop Magento regenerating url-key for store, set following,
    $product->setUrlKey(false);

    //Save the product
    $product->save();
}

This has been tested and it works.