Magento - get filterable attributes by category

Question

I have created a custom navigation module specifically for a website, but I really want to be able to list filterable attributes by a specific category. So for instance my main navigation is:

• Category 1
• Category 2
• Category 3 etc.

I then that when a user mouses over a category, they are then presented with an expanded menu with a few filterable options e.g.:

---

Category 1

View by manufacturer:

• Manufacturer 1
• Manufacturer 2
• Manufacturer 3 etc.

---

I am able to get all filterable attributes for the store, but I want this list to pull in only the filterable attributes per category, as for instance Category 1 may have different manufacturers to Category 2. I then need to cache these results as this will not change often.

Answer 1

Magento uses the model Catalog_Model_Layer to accomplish this, so I'm guessing this may be your best bet. Caveat emptor, I have not tested this code yet:

$layer = Mage::getModel("catalog/layer");
foreach($categories as $categoryid) {
    $category = Mage::getModel("catalog/category")->load($categoryid);
    $layer->setCurrentCategory($category);
    $attributes = $layer->getFilterableAttributes();
    // do something with your attributes
}

Each iteration here will give you an object of the class Mage_Catalog_Model_Resource_Eav_Mysql4_Attribute_Collection, which you should be able to iterate over in a foreach loop to get your desired output.

For caching, try enabling block caching on your site and give the block a cache tag like the following. Magento will cache the HTML output and all will be right with the world:

protected function _construct() {
    $this->addData(array(
        'cache_lifetime' => 3600,
        'cache_tags'     => array(Mage_Catalog_Model_Product::CACHE_TAG),
        'cache_key'      => $someUniqueIdentifierYouCreate,
    ));
}

The cache will only be valid for the key you pass, so make sure that, if the menu is to change (w/o flushing the cache, for instance), that the cache key is different.

Hope that helps!

Thanks, Joe