Invalidate block cache after attribute was edited

Question

How to invalidate block cache after product attribute was edited. E.g. there is a multiselect attribte and if I edit its values in Magento admin I need the cache of the block to be deleted and refreshed.

There are many examples of how to do this when specific product was edited, e.g. on Magento forum: http://www.magentocommerce.com/wiki/5_-_modules_and_development/block_cache_and_html_ouput

protected function _construct()
{
    $this->addData(array(
        'cache_lifetime'    => 120,
        'cache_tags'        => array(Mage_Catalog_Model_Product::CACHE_TAG . "_" . $this->getProduct()->getId()),
        'cache_key'         => $this->getProduct()->getId(),
    ));
}

but how to do this for attributes?

I've found the Mage_Eav_Model_Entity_Attribute::CACHE_TAG constant for attributes but I'm not sure how to use it to delete the cache only when specific attribute was edited:

protected function _construct()
{
    $this->addData(array(
        'cache_lifetime'    => 120,
        'cache_tags'        => array(Mage_Eav_Model_Entity_Attribute::CACHE_TAG),
        'cache_key'         => $product->getResource()->getAttribute('color')->getFrontend()->getValue($product),
    ));
}

Answer 1

If you use 'cache_key' => $product->getResource()->getAttribute('color')->getFrontend()->getValue($product) you don't have to invalidate the cache, it will have different cache key when you edit the product. It would be better to use a key like this one 'cache_key' => 'MY_BLOCK_PRODUCT_' . $product->getId() . '_COLOR_' $product->getColor().