Programmatically modify related products in magento - magento

Question

I'm trying to programmatically manipulate the product relations in a Magento store.
From what I've read, setRelatedLinkData should be the way to go.
As I simple test, I'm just trying to replace a products related products with nothing (i.e. an empty array), however it's not working - the product in question is still showing the related product in the backend.
The test code I'm working with is:
$product = Mage::getModel('catalog/product')->load($product->getId());
$linkData = array();
print_r($linkData);
$product->setRelatedLinkData($linkData);
echo "Save\n";
$r = $product->save();
As mentioned above however the product still has a related product when I reload it in the backend.
NOTE: I don't only want to remove related products, eventually I want to be able to add new ones as well, so a DELTE FROM... SQL query isn't what I am looking for. However if I can't get it to work to remove products, then it's certainly not going to work to add them, so one step at a time :-)

Answer 1

The quickest way I can think of is to use the Link Resource:
app/code/core/Mage/Catalog/Model/Resource/Product/Link.php saveProductLinks
// sample code
$product = Mage::getModel('catalog/product')->load(147);
$linkData = array();
Mage::getResourceModel('catalog/product_link')->saveProductLinks(
$product, $linkData, Mage_Catalog_Model_Product_Link::LINK_TYPE_RELATED
);
and if you want to assign products use the same code but provide this as $linkData:
$linkData = array(
'145' => array('position' => 1),
'146' => array('position' => 2)
);