What options are available to add a calculated attribute to Mage_Core_Model_Product?

Question

We've got a number of attributes which are generated by basic Excel formulas and then bulk-loaded into the catalog via imports. The process results in "extra" attributes which are read-only and shouldn't be altered by individuals.

Ideally these values wouldn't be stored in EAV attributes, but would instead be calculated on-the-fly as needed. I've considered (and not ruled out) extending the catalog/product model to have additional methods for this data, such as:

class My_Extension_Model_Catalog_Product extends Mage_Core_Catalog_Product {

  public function getSomeValue() {

    if (!$x = $this->getX() || !$y = $this->getY()) {
      return null;
    }

    return ($x * $y);
  }
}

The attribute needs to be available to consumers who expect it to behave like any other attribute--they should be able to call Mage::getModel('catalog/product')->load(123)->getSomeValue(); without any extra boilerplate or bootstrapping.

What other options would I have? Would there be events that would let me calculate and set the value when the product is being loaded? Or better could I assign the function when the product is loaded?

Answer 1

If you have a fixed amount of attributes I would suggest to implement a custom extension that creates them using the install script. The calculation can be done by rewriting the Mage_Core_Catalog_Product like you've written above.

As for as events goes you have 2 events for loading products:

1. catalog_product_load_before
2. catalog_product_load_after.

For loading product collections you have

1. catalog_product_collection_load_before
2. catalog_product_collection_load_after.