Get configurable option and value if parent and child known

Question

If I have a configurable product id and an associated child product id, how can i determine the specific attribute id and options used for that combination?

Answer 1

Let's assume that the configurable product id is $mainProductId and the child product id is $childId.
You can get the configurable attributes like this:

$product = Mage::getModel('catalog/product')->setStoreId(Mage::app()->getStore()->getId())->load($mainProductId);
$attributes = $product->getTypeInstance(true)->getConfigurableAttributesAsArray($product); 

Now you can get the child product values like this:

$child = Mage::getModel('catalog/product')->setStoreId(Mage::app()->getStore()->getId())->load($childId);
foreach ($attributes as $attribute){
    //this will get you the id of the option
    echo $attribute['store_label'].':'.$child->getData($attribute['attribute_code'])."<br />"; 
    //if you want the label of the option use the foreach below.
    foreach ($attribute['values'] as $value){
        $childValue = $child->getData($attribute['attribute_code']);
        if ($value['value_index'] == $childValue){
            echo $attribute['store_label'].':'.$value['store_label']."<br />";
        }
    }
}