How to override a Magento controller

Say I want to override Magento Catalog Product controller, say my namespace is Magex and my module name is Powercat.

Firstly, add the following to Powercat/etc/config.xml. What it does is adding another route “prowercat” in addition to “catalog” to frontend. When http://mydomain/catalog/somecontroller/someaction/ is routered, powercat/somecontroller/someaction will be loaded before (see the attribute “before”?) catalog/somecontroller/someaction. If powercat/somecontroller/someaction is available, people get some page when visiting http://mydomain/catalog/somecontroller/someaction/ or http://mydomain/powercat/somecontroller/someaction/. I will not publish the latter url because the whole point of overriding a controller is reusing the Magento original url.

<?xml version="1.0"?>
<config>
<frontend>
<routers>
<catalog>
<args>
<modules>
<anyname before="Mage_Catalog">Magex_Powercat</anyname><!-- the tag name can be any name -->
</modules>
</args>
</catalog>
</frontend>
</config>

Secondly, create a subclass in the following format. “require_once” is essential because controllers are not auto-loaded.

<?php
require_once 'Mage/Catalog/controllers/SomeController.php';
class Magex_Powercat_SomeController extends Mage_Catalog_SomeController
{
//function someAction here
}
?>

Last but not the least, put the overriding controllers into a dedicated module. Otherwise it is very easy to break Magento fallback mechanism. For example, suppose Magex_Powercat has two controllers.

1. Magex_Powercat_IndexController does its own logic (not extending Mage_Catalog_IndexController, and
2. Magex_Powercat_ProductController extends Mage_Catalog_ProductController

The scenarios are:

• When people visit http://mydomain/catalog/product/someaction/, powercat/somecontroller/someaction will be loaded – OK.
• When people visit http://mydomain/catalog/category/someaction/, catalog/category/someaction will be loaded (because Powercat does not have CategoryController, Magento will fallback to Mage’s CategoryController) – OK.
• When people visit http://mydomain/catalog/index/someaction/, if Powercat’s IndexController does not have someAction (only Mage’s IndexController has) – Error happens!
• When people visit http://mydomain/catalog/index/someaction/, if Powercat’s IndexController does have someAction, page will load without error. However, remember Magex_Powercat_IndexController does its own logic? No router to the original logic!