====== How to overload a controller ======

In this example we're overloading Mage_Checkout_CartController::indexAction().

====1. Create your module folders and files====
  - Magento/app/code/local/MyNameSpace/MyModule/etc/config.xml
  - Magento/app/code/local/MyNameSpace/MyModule/controllers/Checkout/CartController.php
  - Magento/app/etc/modules/MyNameSpace_All.xml

====2. Edit /etc/config.xml====
Go to Magento/app/code/local/MyNameSpace/MyModule/etc/config.xml and paste the following xml into it (comments I’m not a 100% sure about are ending with “(?)"):
<code xml>
<?xml version="1.0"?>
<config>
    <modules>
        <MyNameSpace_MyModule>
            <version>0.1.0</version>
        </MyNameSpace_MyModule>
    </modules>
    <global>
        <!-- This rewrite rule could be added to the database instead -->
        <rewrite>
            <!-- This is an identifier for your rewrite that should be unique -->
            <mynamespace_mymodule_checkout_cart>
                <from><![CDATA[#^/checkout/cart/#]]></from>
                <!-- 
                    - mymodule matches the router frontname below 
                    - checkout_cart matches the path to your controller
                    
                    Considering the router below, "/mymodule/checkout_cart/" will be 
                    "translated" to "/MyNameSpace/MyModule/controllers/Checkout/CartController.php" (?)
                -->
                <to>/mymodule/checkout_cart/</to>
            </mynamespace_mymodule_checkout_cart>
        </rewrite>
    </global>
    <!-- 
    If you want to overload an admin-controller this tag should be <admin> instead,
    or <adminhtml> if youre overloading such stuff (?)
    -->
    <frontend>
        <routers>
            <mynamespace_mymodule>
                <!-- should be set to "admin" when overloading admin stuff (?) -->
                <use>standard</use>
                <args>
                    <module>MyNameSpace_MyModule</module>
                    <!-- This is used when "catching" the rewrite above -->
                    <frontName>mymodule</frontName>
                </args>
            </mynamespace_mymodule>
        </routers>
    </frontend>
</config>
</code>

====3. Edit /controllers/Checkout/CartController.php ====
Paste the following php code into Magento/app/code/local/MyNameSpace/MyModule/controllers/Checkout/CartController.php
(the only change we're doing to the indexAction() is adding an error_log() message):
<code php>
<?php
# Controllers are not autoloaded so we will have to do it manually: 
require_once 'Mage/Checkout/controllers/CartController.php';
class MyNameSpace_MyModule_Checkout_CartController extends Mage_Checkout_CartController
{
    # Overloaded indexAction
    public function indexAction()
    {
        # Just to make sure
        error_log('Yes, I did it!');
        parent::indexAction();
    }
}
</code>

====3. Edit Magento/app/etc/modules/MyNameSpace_All.xml====
(This is to activate your module)

<code xml>
<?xml version="1.0"?>
<config>
    <modules>
        <MyNameSpace_MyModule>
            <active>true</active>
            <codePool>local</codePool>
        </MyNameSpace_MyModule>
    </modules>
</config>
</code>

====4. Edit Magento/app/design/frontend/[myinterface]/[mytheme]/layout/checkout.xml====
Add the following to use the same update handle as before:
<code xml>
<mynamespace_mymodule_checkout_cart_index>
    <update handle="checkout_cart_index"/>
</mynamespace_mymodule_checkout_cart_index>
</code>

====5. Point your browser to /checkout/cart/====
Take a look in your php error log and you should find ‘Yes, I did it!’.