Magento – Extending Core Classess for Models, Blocks & Helpers – cheatsheet
General Rules for rewriting Classes in Magento 1.7 (1.8):
<config>
<global>
<!-- models / helpers / resources / etc... -->
<models>
<!-- Module name -->
<module>
<rewrite>
<!-- the tag name is the Model / Block/ Helper to be rewritten -->
<model>
Namespace_Module_Model_Sales_Order_Item
</model>
</rewrite>
</module>
</models>
</global>
</config>1. Example – Rewriting Model Class for the class Mage_Core_Model_Session:
The path to the model : /app/code/core/Mage/Core/Models/Session.php
<config>
<global>
<models> <!-- We are rewriting a Model Class -->
<core> <!-- "core" - because the session Model is in the Core module -->
<rewrite>
<session> <!-- "session" - because its the Model name -->
<!-- The name of the class,
that would rewrite the "Mage_Core_Model_Session" -->
Namespace_Module_Model_Session
</session>
</rewrite>
</core>
</models>
</global>
</config>2. Example – Rewriting the class Mage_Sales_Block_Order_Totals
The path to the block class : /app/code/core/Mage/Sales/Block/Totals.php
<config>
<global>
<blocks>
<!-- We are rewriting a Block Class -->
<!-- "sales" - because this Block is in that module -->
<sales><rewrite>
<!-- "order_totals" - because its the Block name -->
<order_totals>
<!-- The name of the class, that would rewrite the
"Mage_Sales_Block_Order_Totals" -->
Namespace_Module
</order_totals>
</rewrite></sales>
</blocks>
</global>
</config>