Question

I’m learning for the Magento Certification exam and I’m trying to determine under what circumstances are product prices read from the index tables in Magento.
I’m trying to follow Magento’s method’s flow however I’ve stuck after following a few rabbit trails.
Maybe anyone has found it at any point in past?

Answer 1

The product price is only read from the index tables when you are using product collections, i.e. when you are handling several products at a time.
When you get a single product, for example on the product view page, the price is generated on the fly.

And now the explanation with some code references:

When you consider the Mage_Catalog_Model_Product, you will see that the method getFinalPrice() calls $this->getPriceModel()->getFinalPrice($qty, $this);
In turn, the default price model (Mage_Catalog_Model_Product_Type_Price) calculates the price in the method getFinalPrice() and also fires the event catalog_product_get_final_price which is used by some module (I think it was the catalog or the cart price rules) to adjust the price. This method is a calculation “on-the-fly” so without indexes.

In the collection (Mage_Catalog_Model_Resource_Product_Collection) the price indexer is used to reduce the complicated procedure of calcaluting the price for each product.
It defines a map to assign the fields to the appropriate indexed fields:

protected $_map = array('fields' => array(
    'price'         => 'price_index.price',
    'final_price'   => 'price_index.final_price',
    'min_price'     => 'price_index.min_price',
    'max_price'     => 'price_index.max_price',
    'tier_price'    => 'price_index.tier_price',
    'special_price' => 'price_index.special_price',
));

The indexer which does the work is the class Mage_Catalog_Model_Product_Indexer_Price.