Extend Mage_Sales_Helper_Data doesn't work

Question

I would like to add a function in Mage_Sales_Helper_Data without editing or copy of the original file. So I try to extend it, but this code doesn't work

I have created a config.xml in this folder app\code\local\ML\etc

<?xml version="1.0"?>

<config>
    <modules>
       <ML_Sales>
            <version>0.0.1</version>
       </ML_Sales>
   </modules>
   <global>
      <helpers>
       <sales>
         <rewrite>
           <data>ML_Sales_Helper_Data</data>
         </rewrite>
        </sales>
      </helpers>
   </global>
</config>

And then in app\code\local\ML\Sales\Helper I have created Data.php

<?php 
require_once('Mage/Sales/Helper/Data.php'); 
class ML_Sales_Helper_Data extends Mage_Core_Helper_Data {
    public function getOrderHistoryUrl()
    {
        return $this-> _getUrl('sales/order/history');

    }  

}
?>

Finally into my app\design\frontend\my_package\default\layout\local.xml I wrote this code for get the link of "My Order" on my account navigation

 <reference name="top.links">
            <action method="addLink" translate="label" module="sales">
                <label>Orders</label>
                <url helper="sales/getOrderHistoryUrl"/>
                <title>My Orders</title><prepare/>
                <urlParams/>
                <position>50</position>
            </action>        
</reference>

and also in app\etc\modules

 <ML_Sales>
        <active>true</active>
        <codePool>local</codePool>
     </ML_Sales>        

What is wrong? Can someone please help me?

Answer 1

first of all declare the helper for your module in config.xml as below

<global>
    <helpers>
        <ml_sales>
            <class>ML_Sales_Helper</class>
        </ml_sales>
        <sales>
            <rewrite>
                <data>ML_Sales_Helper_Data</data>
            </rewrite>
        </sales>
    </helpers>
</global>

Now in your app\code\local\ML\Sales\Helper\Data.php the content goes like this

<?php 
class ML_Sales_Helper_Data extends Mage_Sales_Helper_Data {
    public function getOrderHistoryUrl()
    {
        echo 'hello'; exit;
        return $this-> _getUrl('sales/order/history');

    }  

}
?>

in your app\design\frontend\my_package\default\layout\local.xml

<reference name="top.links">
    <action method="addLink" translate="label" module="ml_sales">
        <label>Orders</label>
        <url helper="ml_sales/getOrderHistoryUrl"/>
        <title>My Orders</title>
        <prepare/>
        <urlParams/>
        <position>50</position>
    </action>        
</reference>

after doing this clear the cache and check

Note:- Please check in the xml file there should not be any spaces in the xml file.otherwise this will give error.

Answer 2

You don't need this line in your helper require_once('Mage/Sales/Helper/Data.php');. The class will be autoloaded.

Also, your new class should extend the original helper

 class ML_Sales_Helper_Data extends Mage_Sales_Helper_Data

And remember to add the app/etc/modules/ML_Sales.xml file that tells magento to pick up your module

Answer 3

Follow this steps and it should work

1. app/code/local/ML/Sales/etc/config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <ML_Sales>
            <version>0.1.0</version>
        </ML_Sales>
    </modules>
    <global>
        <helpers>
            <sales>
                <class>ML_Sales_Helper</class>
            </sales>
            <sales>
                <rewrite>
                    <data>ML_Sales_Helper_Sales_Data</data>
                </rewrite>
            </sales>
        </helpers>
    </global>
</config> 

2. app/code/local/ML/Sales/Helper/Data.php

<?php
class ML_Sales_Helper_Data extends Mage_Core_Helper_Abstract
{
}

3. app/code/local/ML/Sales/Helper/Sales/Data.php

<?php
class ML_Sales_Helper_Sales_Data extends Mage_Sales_Helper_Data
{
    protected function getOrderHistoryUrl()
    {
        return $this-> _getUrl('sales/order/history');
    }  
}

4. app/etc/modules/ML_Sales.xml

<?xml version="1.0"?>
<config>
  <modules>
    <ML_Sales>
      <active>true</active>
      <codePool>local</codePool>
      <version>0.1.0</version>
    </ML_Sales>
  </modules>
</config>