Many to Many relationship shown in the grid

In Controller
protected function gridCategoryDescription($data,$row)
    {
       return $this->_lastProductId != $data->id ? $data->discription : '';          
    }

protected function gridCategoryPrice($data,$row)
    {
        if($this->_lastProductId != $data->id)
        {
            $this->_lastProductId = $data->id;
            return $data->code;
        }
        else
             return '';
    }

In view

array(            

'name'=>'discription',

'value'=>array($this,'gridCategoryDescription')

),

array(            

'name'=>'code',

'value'=>array($this,'gridCategoryPrice')

),