AutoUpselling Based on Orders

config.xml

<?xml version="1.0"?>
<config>
    <global>
        <events>
            <sales_order_place_after>
                <observers>
                    <custom>
                        <type>singleton</type>
                        <class>custom/autoupsell_observer</class>
                        <method>autoUpsell</method>
                    </custom>
                </observers>
            </sales_order_place_after>
        </events>
    </global>
</config>

Observer.php

<?php

class Custom_Modul_Model_Autoupsell_Observer
{
    /**
     * @mageEvent sales_order_place_after
     */
    public function autoUpsell($event)
    {
        $upsell = Mage_Catalog_Model_Product_Link::LINK_TYPE_UPSELL;
        $order = $event->getOrder();
        $ids = array();
        /* @var $order Mage_Sales_Model_Order */
        foreach($order->getAllItems() as $_product)
        {
            /* @var $_product Mage_Sales_Model_Order_Item */
            $_id = $_product->getProductId();
            $ids[] = $_id;
        }
        if(count($ids) <= 1)
        {
            return $this;
        }
        // 
        foreach($ids as $_id)
        {
           foreach($ids as $_linked_id)
           {
               if($_id != $_linked_id)
               {
                   $this->_connection()->insertOnDuplicate($this->getTableName('catalog/product_link'), array(
                       'product_id' => $_id,
                       'linked_product_id' => $_linked_id,
                       'link_type_id' => $upsell,
                   ));
               }
           }
        }
        return $this;
    }

    /**
     * 
     * @return Mage_Core_Model_Resource
     */
    protected function _resoruce()
    {
        return Mage::getSingleton('core/resource');
    }

    /**
     * 
     * @return Varien_Db_Adapter_Interface
     */
    protected function _connection($type = 'core_write')
    {
        return $this->_resoruce()
                ->getConnection($type);
    }

    /**
     * 
     * @param string $modelEntity
     * @return string
     */
    protected function getTableName($modelEntity)
    {
        return $this->_resoruce()->getTableName($modelEntity);
    }
}