How to add a column for example customer group id in Magento's Admin Order Grid

Question

I want an additional column in the Order(s) Grid for Admin. Assuming its Customer Group Id.

My app/etc/modules/MyProject_Adminhtml looks like:

<?xml version="1.0"?>

<config>
    <modules>
        <MyProject_Adminhtml>
            <active>true</active>
            <codePool>local</codePool>
            <depends>
                <Mage_Sales />
            </depends>
        </MyProject_Adminhtml>
    </modules>
</config>

My app/code/local/MyProject/Adminhtml/etc/config.xml looks like:

<?xml version="1.0"?>
<config>
    <modules>
        <MyProject_Adminhtml>
            <version>1.0.0</version>
        </MyProject_Adminhtml>    
    </modules>

    <global>
          <blocks>
            <adminhtml>
                <rewrite>
                    <sales_order_grid>MyProject_Adminhtml_Block_Sales_Order_Grid</sales_order_grid>
                </rewrite>
            </adminhtml>
        </blocks>

      </global>

  </config>

And in app/code/local/MyProject/Adminhtml/Block/Sales/Order/Grid.php I have overridden Mage_Adminhtml_Block_Sales_Order_Grid

class MyProject_Adminhtml_Block_Sales_Order_Grid extends Mage_Adminhtml_Block_Sales_Order_Grid
{

    protected function _prepareColumns()
    {
        .... unchanged code from Mage_Adminhtml_Block_Sales_Order_Grid::_prepareColumns ...

        $this->addColumn('customer_group_id', array(
            'header' => Mage::helper('sales')->__('Customer Group Id'),
            'index' => 'customer_group_id',
            'type'  => 'text',
        ));

         .... unchanged code from Mage_Adminhtml_Block_Sales_Order_Grid::_prepareColumns ...
    }
}

Is there something I am missing because I don't see anything in Order Grid. I am using Magento 1.4.1.1

On Anda B's comment I wrote the following line:

var_dump($this->getLayout()->createBlock('MyProject_Adminhtml_Block_Sales_Order_Grid'));

in app/code/core/Mage/Adminhtml/controllers/Sales/Order/CreateController.php

Then, I selected 'Create New Order' and Cancel the order to see the result of execution of var_dump, and I see the following:

/var/www/magento/var/report/72990635: line 10: syntax error near unexpected token `}' /var/www/magento/var/report/72990635: line 10: `#9 {main}";s:3:"url";s:80:"/index.php/admin/sales_order_create/cancel/key/0624033594dd63d9e145fc538f4c6bbb/";s:11:"script_name";s:10:"/index.php";s:4:"skin";s:5:"admin";}'

Answer 1

In modules/etc you have Atzen_Adminhtml but your project is MyProject_Adminhtml. Except this problem the code should work: even if you don't have the customer_group_id in sales table, the new column should appear in the grid.