Adding data to Magento grid collection destroys pager

in my开发者_JS百科 own Magento Extension I'm using a grid block, to display the collection of data in my db table. Everything works fine so far and the standard pagination from magento works, too.

I now want to add some random data, which isn't in the db table, to the collection to show it in my grid. If I try as follow the pagination stops working:

class My_own_Block_Admin_Main_Grid extends Mage_Adminhtml_Block_Widget_Grid
{
    protected function _prepareCollection {

         // Load the collection
         $collection = getResourceModel('sales/order_grid_collection');

         // Add custom data
         $collection->addToAll('example', 'This is a test');

         // Set the collection
         $this->setCollection($collection);
         return parent::_prepareCollection();   
    }
}

The pagination is effectless now. Page 1 is the same as 2 and shows all entries.

What's the right and working way to a data to the collection without breaking the pagination?

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The answer to that is prolem is the following thread

http://www.magentocommerce.com/boards/viewthread/192232/#t239222