rewrite block sales order grid [duplicate]

Question

My website uses version 1.7 and in fact I would like to add a column in the view of commandes.my config file:

<?xml version="1.0"?>
  <config>
   <modules>
      <Digitgold_AddColumnInfoPaiement>
         <version>1.0.0</version>
      </Digitgold_AddColumnInfoPaiement>
  </modules>
  <global>
    <blocks>
        <adminhtml>
            <rewrite>
                <sales_order_grid>Digitgold_AddColumnInfoPaiement_Block_Adminhtml_Sales_Order_Grid</sales_order_grid>
            </rewrite>
        </adminhtml>
    </blocks>
  </global>
</config>

and this is my class :

class Digitgold_AddColumnInfoPaiement_Adminhtml_Block_Sales_Order_Grid extends  Mage_Adminhtml_Block_Sales_Order_Grid
{

 public function __construct()
 {
    parent::__construct();
    $this->setId('sales_order_grid');
    $this->setUseAjax(true);
    $this->setDefaultSort('created_at');
    $this->setDefaultDir('DESC');
    $this->setSaveParametersInSession(true);
  }

protected function _prepareColumns()
 {
    $this->addColumn('payement', array(
        'header'=> Mage::helper('sales')->__('Mode de Paiement'),
        'width' => '120px',
        'index' => 'payement',
         ));
}
}

the problem is header appears only of the admin and below is all white.

Answer 1

Change <sales_order> to <sales_order_grid>

See How to extend Magento Order Grid?

E.g

<blocks>
   <adminhtml>
     <rewrite>
      <sales_order_grid>Inchoo_Test_Block_Adminhtml_Order_Grid</sales_order_grid>
     </rewrite>
   </adminhtml>
</blocks>

Please note: The above method is NOT the best option to accomplish this.

Method #2

Assuming that the field is added to sales_flat_order and sales_flat_order_grid db

In layout.xml (admin)

<?xml version="1.0"?>
<layout>
    <add_order_grid_column_handle>
        <reference name="sales_order.grid">
            <action method="addColumnAfter">
                <columnId>payement</columnId>
                <arguments module="sales" translate="header">
                    <header>Mode de Paiement</header>
                    <index>payement</index>
                    <type>text</type>
                    <width>110px</width>
                </arguments>
                <after>shipping_name</after>
            </action>
        </reference>
    </add_order_grid_column_handle>
    <adminhtml_sales_order_grid>
        <update handle="add_order_grid_column_handle" />
    </adminhtml_sales_order_grid>
    <adminhtml_sales_order_index>
        <update handle="add_order_grid_column_handle" />
    </adminhtml_sales_order_index>
<layout>

Answer 2

Rewriting the Sales Order Grid is not the best solution as this is not needed because there is a Magento build-in solution that allows you to add extra columns. I made a complete example extension for this in add column to sales/orders grid

This extension adds a column to the sales_flat_order_grid table, populates the field for the current orders and an observer that will insert the data in the before save event every time an order is saved.