Magento coding tip: How to override core model class?

As a Magento developer you already know that you shouldn't mess around with core files.
So what is the best ways to edit a core model class? Override!

Let's say we would like to override core Mage_Sales_Model_Order class.
First thing you have to do is to add some lines to the config file of your module:
app/code/local/Kiwee/MyModule/etc/config.xml

And put your class name that will override core class:

<config>
    <global>
       <models>
          <sales>
              <rewrite>
                  <order>Kiwee_MyModule_Model_Order</order>
              </rewrite>
          </sales>
       </models>
    </global>
</config>

Create your class file:
app/code/local/Kiwee/MyModule/models/Order.php

And add class code to the file:

class Kiwee_MyModule_Model_Order extends Mage_Sales_Model_Order
{
	// your code here
}

Et voilà! Don't forget to clear the cache or even better disable it completely for the testing purpose.

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