Custom module with custom product list

Question

I'm trying to create a new page that lists a custom selection of products (basically a list of SKUs returned from an external service) that uses the default magento layered navigation.

I've been using this as a guideline: http://www.techytalk.info/adding-layered-navigation-custom-controller-action-magento/

But I've hitten a little snag when I'm trying to filter the products, in my:

app/code/local/xyzname/abcname/Model/Catalog/Layer.php

public function prepareProductCollection($collection) {
    parent::prepareProductCollection($collection);

    $collection
        ->addAttributeToFilter( 'sku', array( 'in' => $this->skus ) );


    //echo $collection->getSelectSql(true);die;

    return $this;
}

I'm getting this error:

... Column not found: 1054 Unknown column 'e.sku' in 'where clause', query was: ...

I've read that I could use ->getSelect()->join... to compensate for that missing sku, but databases/sql is something I'm very, very noob about.

Right now the $skus is just an static array.

Answer 1

The following code should work better (in some cases e denotes catalog_product_index_price table which doesn't have sku column):

    $condition = count($this->skus) 
        ? "sku_filter.sku IN ('" . implode("', '", $this->skus) . "')"
        : "sku_filter.entity_id IS NULL";

    $collection->getSelect()
        ->join(
            array('sku_filter' => Mage::getSingleton('core/resource')->getTableName('catalog/product')),
            "sku_filter.entity_id = e.entity_id AND $condition",
            null
        );