Layered navigation filters for grouped products only

Question

Well, I'm having a category filled only with grouped products and I want these ones to be filtered by their associated ( and simple ) products's attributes.

Until now I've used a dirty workaround : I've left only one simple product to be visible to catalog but hidden by html & css.
That way the attributes were appearing and I could use them for the grouped products also, but I've noticed that layered navigation dissapears if that hidden simple product is not appearing when I filter by price.

Any ideas or workarounds?

Thanks.

Answer 1

You need to rewrite how Mage_Catalog_Model_Layer builds the attribute collection using the current product collection's attribute sets:

protected function _getSetIds()
{
    $key = $this->getStateKey().'_SET_IDS';
    $setIds = $this->getAggregator()->getCacheData($key);

    if ($setIds === null) {
        $setIds = $this->getProductCollection()->getSetIds();
        $this->getAggregator()->saveCacheData($setIds, $key, $this->getStateTags());
    }

    return $setIds;
}

For this context, you'll want to check the product collection for grouped products and return the attribute set IDs of grouped children. These are then evaluated in getFilterableAttributes():

public function getFilterableAttributes()
{
    $setIds = $this->_getSetIds();
    if (!$setIds) {
        return array();
    }
    /** @var $collection Mage_Catalog_Model_Resource_Product_Attribute_Collection */
    $collection = Mage::getResourceModel('catalog/product_attribute_collection');
    $collection
        ->setItemObjectClass('catalog/resource_eav_attribute')
        ->setAttributeSetFilter($setIds)
        ->addStoreLabel(Mage::app()->getStore()->getId())
        ->setOrder('position', 'ASC');
    $collection = $this->_prepareAttributeCollection($collection);
    $collection->load();

    return $collection;
}

You will likely need to deal with the cache key. I would develop with block caching off and then test extensively with it on.