Magento. Overwrite core files

Question

I try to overwrite Magento Block file /app/code/core/Mage/Checkout/Block/Onepage/Success.php but I cant find problem why it doesn`t work.

/app/code/local/Mandarin/AfterBuy/etc/config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <Mandarin_AfterBuy>
            <version>0.1.0</version>
        </Mandarin_AfterBuy>
    </modules>
    <global>
        <blocks>
            <checkout>
                <rewrite>
                    <onepage_success>Mandarin_AfterBuy_Block_Onepage_Success</onepage_success>
                </rewrite>
            </checkout>
        </blocks>
    </global> 
</config>

/app/code/local/Mandarin/AfterBuy/Block/Onepage/Success.php:

<?php
class Mandarin_AfterBuy_Block_Onepage_Success extends Mage_Checkout_Block_Onepage_Success
{
  /*...Some methods..*/
}

/app/etc/modules/Mandarin_AfterBuy.xml:

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

Help me please, where there is could be mistake? I use magento 1.7.

Thanks.

Answer 1

In your declaration file ./app/etc/modules/Mandarin_AfterBuy.xml:

Mandarin_AfteBuy -> Mandarin_AfterBuy
                                 ^

Answer 2

Do not owerride any core files in future ! ))