Extending sales order Grid breaking Pagination - magento

Question

I am trying to extend the sales-> order Grid by Sku and product name.
I managed to get the sku and name in the Grid with all the data.
Now the problem is it's breaking the pagination.
Can anyone please help me with that.
Code:
class Mage_Adminhtml_Block_Sales_Order_Grid extends Mage_Adminhtml_Block_Widget_Grid
{
public function __construct()
{
parent::__construct();
$this->setId('sales_order_grid');
$this->setUseAjax(true);
$this->setDefaultSort('created_at');
$this->setDefaultDir('DESC');
$this->setSaveParametersInSession(true);
}
/**
* Retrieve collection class
*
* #return string
*/
protected function _getCollectionClass()
{
return 'sales/order_grid_collection';
}
protected function _prepareCollection()
{
// Custom code
$collection = Mage::getResourceModel($this->_getCollectionClass())
->join(
'sales/order_item',
'`sales/order_item`.order_id=`main_table`.entity_id',
array(
'sku' => new Zend_Db_Expr('group_concat(`sales/order_item`.sku SEPARATOR ",")'),
'name' => new Zend_Db_Expr('group_concat(`sales/order_item`.name SEPARATOR ",")'),
)
);
$collection->getSelect()->group('entity_id');
$this->setCollection($collection);
return parent::_prepareCollection();
}
protected function _prepareColumns()
{
// Custom code
$this->addColumn('name', array(
'header' => Mage::helper('Sales')->__('Name'),
'width' => '100px',
'index' => 'name',
'type' => 'text',
));
$this->addColumn('sku', array(
'header' => Mage::helper('Sales')->__('Sku'),
'width' => '100px',
'index' => 'sku',
'type' => 'text',
));
$this->addColumn('real_order_id', array(
'header'=> Mage::helper('sales')->__('Order #'),
'width' => '80px',
'type' => 'text',
'index' => 'increment_id',
));
if (!Mage::app()->isSingleStoreMode()) {
$this->addColumn('store_id', array(
'header' => Mage::helper('sales')->__('Purchased From (Store)'),
'index' => 'store_id',
'type' => 'store',
'store_view'=> true,
'display_deleted' => true,
));
}
$this->addColumn('created_at', array(
'header' => Mage::helper('sales')->__('Purchased On'),
'index' => 'created_at',
'type' => 'datetime',
'width' => '100px',
));
$this->addColumn('billing_name', array(
'header' => Mage::helper('sales')->__('Bill to Name'),
'index' => 'billing_name',
));
$this->addColumn('shipping_name', array(
'header' => Mage::helper('sales')->__('Ship to Name'),
'index' => 'shipping_name',
));
$this->addColumn('base_grand_total', array(
'header' => Mage::helper('sales')->__('G.T. (Base)'),
'index' => 'base_grand_total',
'type' => 'currency',
'currency' => 'base_currency_code',
));
$this->addColumn('grand_total', array(
'header' => Mage::helper('sales')->__('G.T. (Purchased)'),
'index' => 'grand_total',
'type' => 'currency',
'currency' => 'order_currency_code',
));
$this->addColumn('status', array(
'header' => Mage::helper('sales')->__('Status'),
'index' => 'status',
'type' => 'options',
'width' => '70px',
'options' => Mage::getSingleton('sales/order_config')->getStatuses(),
));
if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/view')) {
$this->addColumn('action',
array(
'header' => Mage::helper('sales')->__('Action'),
'width' => '50px',
'type' => 'action',
'getter' => 'getId',
'actions' => array(
array(
'caption' => Mage::helper('sales')->__('View'),
'url' => array('base'=>'*/sales_order/view'),
'field' => 'order_id'
)
),
'filter' => false,
'sortable' => false,
'index' => 'stores',
'is_system' => true,
));
}
$this->addRssList('rss/order/new', Mage::helper('sales')->__('New Order RSS'));
$this->addExportType('*/*/exportCsv', Mage::helper('sales')->__('CSV'));
$this->addExportType('*/*/exportExcel', Mage::helper('sales')->__('Excel XML'));
return parent::_prepareColumns();
}
Problem is with my Collection. I am working here with core class but I will override it once I get my result.

Answer 1

You have a GROUP BY clause in your collection, and the grid pager uses $collection->getSize() to determine the number of pages. The problem is that getSize() applies a SELECT COUNT(*) to the collection, and fetches the first column of the first row to get the number of results. With the GROUP BY still applied, the pager then considers that there is only one result.
To prevent this problem, you should either use your own orders collection with a relevant getSize(), or use sub-queries to retrieve SKUs and names.