Is there a confirmed way to add a product to the cart using URL in magento 1.8?

Question

There are loads of articles and posts about doing this in previous versions using several different URL strings, all of which none work in Magento 1.8

Has anyone actually figured out a way to do it yet?

For example, this is listed on the Magento Wiki and was added in 2010: http://www.magentocommerce.com/wiki/4_-_themes_and_template_customization/catalog/adding_a_product_to_the_cart_via_querystring

/path/to/app/checkout/cart/add?product=[id]&qty=[qty]

However when clicked, this link just refreshes the cart.

Just incase anyone wants to see how I'm trying to code it:

<button type="button" title="Add Loan Phone" class="button" onclick="setLocation('URL HERE')"><span class="green">Add a Loan Phone (+£10)</span></button>

Answer 1

You can use the checkout's cart helper for that

echo (string)Mage::helper('checkout/cart')->getAddUrl($_product);

Make sure $_product is an instance of the class Mage_Catalog_Model_Product

So putting it all together as requested

<?php $_product = Mage::getModel('catalog/product')->load([product id]);?>

<button type="button" title="Add Loan Phone" class="button" onclick="setLocation('<?php echo (string)Mage::helper('checkout/cart')->getAddUrl($_product);?>')"><span class="green">Add a Loan Phone (+£10)</span></button>