store values inside Magento attributes - php

Question

I am setting up a magento feed and I stuck since I need the system to auto calculate the values for the last few attributes.
how can I have magento create an attribute with the MAX sale price, and MAX list price, and Rating, also I need 2 more attribites 1 for discount amount and the last for discount percentage.
any help is appreciated.

Answer 1

If I understand your problem correctly, you could probabaly use the afterLoad event of some Magento objects. This would work for most models within Magento.
Preface
In general, most of the Model used in Magento (that is, e.g. products, orders, etc. in the core libraries and every model you would define in a custom module with db access) extend the class Mage_Core_Model_Abstract, which provides certain "event"-based methods.
These methods are _afterDelete, _afterDeleteCommit, _afterLoad, _afterSave, _afterSavecommit, _beforeLoad, _beforeSave and _beforeDelete (in Magento >1.4.2.0).
Overriding a model
I assume, you would like to have automatic caluclated attributes on a product. The first step here would be to create a new custom module which overrides the core model for Magento products. In a newly created model, you can use the following entry in ./app/code/local/YourNamespace/YourModule/etc/config.xml:
[...]
<global>
[...]
<models>
<catalog>
<rewrite>
<product>YourNamespace_YourModule_Model_Product</product>
</rewrite>
</catalog>
</models>
[...]
<global>
[...]
You can then overwrite the Product Model as shown in a file called ./app/code/local/YourNamespace/YourModule/Model/Product.php:
<?php
class YourNamespace_YourModule_Model_Product extends Mage_Catalog_Model_Product
{
protected function _afterLoad()
{
parent::_afterLoad();
//your voodoo goes here.
$my_awesome_calculated_value = $this->getData('my_awesome_float_attribute') / 2;
$this->setData('my_awesome_calculated_value', $my_awesome_calculated_value);
}
}
With this, as long as you have a model loaded, you have the opportunity to use that calculated value in whatever way you could conceive. Keep in mind, that this code is executed every time a product is loaded, which can be quite often (if it's a product, that is), so don't get too temerarious with this.
Also keep in mind, that this value is lost, after your code execution is finished, as the value exists only as long as the model "lives". If you want to store it, you could also override _beforeSave or create placeholder attributes, which are filled each time a model is loaded and then saved afterwards.
For the attributes for discount_amountand discount_percentage i would use the same strategy:
load the model
calculate the dicount_amount and discount_percentage in _afterLoad and store it on the model
work with the model.
Addendum
If you're new to Magento and don't know explicitly how to create new modules, you can start with http://www.magentocommerce.com/wiki/5_-_modules_and_development/0_-_module_development_in_magento/custom_module_with_custom_database_table (although it's a bit outdated) or look around stackoverflow.
lg,
and good luck,
flo