Helper to preload all simple products and configurable attributes for a product collection containing configurable products.

VinaiKopp_ProductList_Helper_Data.php

<?php

class VinaiKopp_ProductList_Helper_Data extends Mage_Core_Helper_Abstract
{
    /**
     * Base product collection to work on
     * 
     * @var Mage_Catalog_Model_Resource_Product_Collection
     */
    protected $_productCollection;

    /**
     * Array of the ids of configurable products from $_productCollection
     * 
     * @var array
     */
    protected $_configurableProductIds;

    /**
     * All associated simple products from configurables in $_configurableProductIds
     * 
     * @var Mage_Catalog_Model_Resource_Product_Type_Configurable_Product_Collection
     */
    protected $_simpleProducts;

    /**
     * Array of associated simple product ids.
     * The array index are configurable product ids, the array values are
     * arrays of the associated simple product ids.
     * 
     * @var array
     */
    protected $_associatedSimpleProducts;

    /**
     * Array keys are the configurable product ids,
     * the values are configurable attribute ids 
     * 
     * @var array
     */
    protected $_configurableProductAttributes;

    /**
     * Array of all configurable attribute codes used in the current collection.
     * No association of which product used which configurable attributes.
     * 
     * @var array
     */
    protected $_configurableAttributeCodes;

    /**
     * Set the product collection.
     * If not specified defaults to the product collection of the layer model.
     * 
     * @param Mage_Catalog_Model_Resource_Product_Collection $collection
     * @return $this
     */
    public function setProductCollection(Mage_Catalog_Model_Resource_Product_Collection $collection)
    {
        $this->_productCollection = $collection;
        return $this;
    }

    /**
     * Return the attribute values of the associated simple products
     * 
     * @param Mage_Catalog_Model_Product $product Configurable product
     * @param int|Mage_Core_Model_Store $store
     * @return array
     */
    public function getProductConfigurableAttributes(Mage_Catalog_Model_Product $product, $store = null)
    {
        if ($product->getTypeId() != Mage_Catalog_Model_Product_Type_Configurable::TYPE_CODE) {
            return array();
        }

        $storeId = Mage::app()->getStore($store)->getId();

        $usedProducts = $this->_getAssociatedSimpleProducts($product);
        if (! $usedProducts) {
            // This will happen if two configurable products share the same simple product
            // The second configurable product will be skipped
            return array();
        }
        $attributeIds = $this->_getProductConfigurableAttributeIds($product);
        $allAttributeCodes = $this->_getConfigurableAttributeCodes();
        
        $data = array();
        foreach ($attributeIds as $attributeId) {
            $code = $allAttributeCodes[$attributeId];
            $sourceModel = Mage::getSingleton('eav/config')
                ->getAttribute('catalog_product', $code)
                ->setStoreId($storeId)
                ->getSource();
            foreach ($usedProducts as $simpleProduct) {
                // check if the attribute is set in case it isn't set to be used in product listing
                if (isset($simpleProduct[$code])) {
                    $value = $simpleProduct[$code];
                    $data[$code][$value] = $sourceModel->getOptionText($value);
                }
            }
        }
        return $data;
    }

    /**
     * Return array of configurable attribute ids of the given configurable product
     * 
     * @param Mage_Catalog_Model_Product $product
     * @return array
     */
    protected function _getProductConfigurableAttributeIds(Mage_Catalog_Model_Product $product)
    {
        $attributes = $this->_getConfigurableProductAttributes();
        $productId = $product->getId();
        if (! isset($attributes[$productId])) {
            Mage::throwException(
                $this->__('Product %d is not part of the current product collection', $product->getId())
            );
        }
        return explode(',', $attributes[$productId]);
    }

    /**
     * Load all configurable attributes used in the current product collection
     *
     * @return array
     */
    protected function _getConfigurableProductAttributes()
    {
        if (! $this->_configurableProductAttributes) {
            $productIds = $this->_getConfigurableProductIds();
            $attributes = $this->_getConfigurableAttributesForProductsFromResource($productIds);

            $this->_configurableProductAttributes = $attributes;
        }
        return $this->_configurableProductAttributes;
    }

    /**
     * This method actually would belong into a resource model, but for easier
     * reference I dropped it into the helper here.
     * 
     * @param array $productIds
     * @return array
     */
    protected function _getConfigurableAttributesForProductsFromResource(array $productIds)
    {
        /** @var Mage_Core_Model_Resource_Helper_Mysql4 $resourceHelper */
        $resourceHelper = Mage::getResourceHelper('core');
        $resource = Mage::getSingleton('core/resource');
        $adapter = $resource->getConnection('catalog_read');
        $select = $adapter->select()
            ->from($resource->getTableName('catalog/product_super_attribute'), array('product_id'))
            ->group('product_id')
            ->where('product_id IN(?)', $productIds);
        $resourceHelper->addGroupConcatColumn($select, 'attribute_ids', 'attribute_id');

        $attributes = $adapter->fetchPairs($select);
        return $attributes;
    }

    /**
     * Return array of all configurable attributes in the current collection.
     * Array indexes are the attribute ids, array values the attribute code
     * 
     * @return array
     */
    protected function _getConfigurableAttributeCodes()
    {
        if (is_null($this->_configurableAttributeCodes)) {
            // build list of all configurable attribute codes for the current collection
            $this->_configurableAttributeCodes = array();
            foreach ($this->_getConfigurableProductAttributes() as $attributes) {
                $attributes = explode(',', $attributes);
                foreach ($attributes as $attributeId) {
                    if ($attributeId && ! isset($this->_configurableAttributeCodes[$attributeId])) {
                        $attributeModel = Mage::getSingleton('eav/config')
                            ->getAttribute('catalog_product', $attributeId);
                        $this->_configurableAttributeCodes[$attributeId] = $attributeModel->getAttributeCode();
                    }
                }
            }
        }
        return $this->_configurableAttributeCodes;
    }

    /**
     * Return the current product collection
     * 
     * @return Mage_Catalog_Model_Resource_Product_Collection
     */
    protected function _getProductCollection()
    {
        if (! $this->_productCollection) {
            $this->_productCollection = Mage::getSingleton('catalog/layer')->getProductCollection();
        };
        return $this->_productCollection;
    }

    /**
     * Return array of ids of configurable products in the current product collection
     * 
     * @return array
     */
    protected function _getConfigurableProductIds()
    {
        if (is_null($this->_configurableProductIds)) {
            $this->_configurableProductIds = array();
            $products = $this->_getProductCollection();
            foreach ($products as $product) {
                if ($product->getTypeId() == Mage_Catalog_Model_Product_Type_Configurable::TYPE_CODE) {
                    $this->_configurableProductIds[] = $product->getId();
                }
            } 
        }
        return $this->_configurableProductIds;
    }

    /**
     * Return all associated simple products for the configurable products in
     * the current product collection.
     * Array key is the configurable product
     * 
     * @return array
     */
    protected function _getSimpleProducts()
    {
        if (is_null($this->_simpleProducts)) {
            $parentIds = $this->_getConfigurableProductIds();
            $collection = Mage::getResourceModel('catalog/product_type_configurable_product_collection')
                ->addAttributeToFilter('is_saleable', 1)
                ->addAttributeToSelect('parent_id');
            $collection->getSelect()->where('link_table.parent_id IN(?)', $parentIds);
            $collection->groupByAttribute('entity_id');
            
            $attributeCodes = $this->_getConfigurableAttributeCodes();
            $collection->addAttributeToSelect($attributeCodes);
            
            foreach ($collection->getItems() as $row) {
                $row = $row->getData();
                $simpleId = $row['entity_id'];
                $parentId = $row['parent_id'];
                $this->_simpleProducts[$simpleId] = $row;
                $this->_associatedSimpleProducts[$parentId][] = $simpleId;
            }
        }
        return $this->_simpleProducts;
    }

    /**
     * Return array of associated simple product data
     * 
     * @param Mage_Catalog_Model_Product $product The configurable product
     * @return array Data for each associated simple product as array
     */
    protected function _getAssociatedSimpleProducts(Mage_Catalog_Model_Product $product) {
        $simpleProducts = array();
        $parentId = $product->getId();
        $allSimpleProducts = $this->_getSimpleProducts();
        // If two configurable products share the same simple product the
        // second one will not have a matching record in $this->_associatedSimpleProducts 
        if (isset($this->_associatedSimpleProducts[$parentId])) {
            foreach ($this->_associatedSimpleProducts[$parentId] as $simpleProduct) {
                $simpleProducts[] = $allSimpleProducts[$simpleProduct];
            }
        }
        return $simpleProducts;
    }

    /**
     * The methods listed below belong into the resource model layer. For easier
     * reference as an educational example I've listed them in this helper though.
     *
     * @see self::_getConfigurableAttributesForProductsFromResource()
     * @see self::_getSimpleProducts()
     * @return VinaiKopp_ProductList_Model_Resource_Configurable_Attributes
     */
    protected function _getResourceModel()
    {
        return Mage::getResourceSingleton('vinaikopp_productlist/configurable_attributes');
    }
}