Magento store/save data in custom columns

Question

I added two text columns to sales_flat_quote_item in order to store data and for other reasons When i add product to cart. my problem is that i cant save the data. i tried a lot of examples but without any success. Config.xml file :

 <events>
        <catalog_product_load_after>
            <observers>
                <iwp_package>
                    <type>model</type>
                    <class>iwp_package/observer</class>
                    <method>catalogProductLoadAfter</method>
                </iwp_package>
            </observers>
        </catalog_product_load_after>
    </events>

here i add the coulmns :

$installer = $this;
$connection = $installer->getConnection();
$installer->startSetup();
$installer->getConnection()
    ->addColumn($installer->getTable('sales/quote_item'),
    'pack_name',
    array(
        'type' => Varien_Db_Ddl_Table::TYPE_TEXT,
        'nullable' => true,
        'default' => null,
        'comment' => 'pack_name'
    )
);
$installer->endSetup();

This is the code in my observer where i try to save the data :

$quote_item  = Mage::getModel('sales/quote_item')->load($quote->Id);
$quote_item->setPackName($string);
$quote_item->save();

any help?

Answer 1

try this event it gets triggered only when items gets added to cart

 <events>
        <checkout_cart_add_product_complete>
            <observers>
                <iwp_package>
                    <type>model</type>
                    <class>iwp_package/observer</class>
                    <method>catalogProductLoadAfter</method>
                </iwp_package>
            </observers>
        </checkout_cart_add_product_complete>
    </events>

EDIT

Am Assuming that $quote has quote object, so further you have to loop through all the items in cart.

For that you can try below code snippet

foreach ($quote->getAllItems() as $item) {
    $item->setPackName($string);
    $item->save();
}

OR

foreach ($quote->getAllItems() as $item) {
    $quote_item  = Mage::getModel('sales/quote_item')->load($item->getItemId());
    $quote_item->setPackName($string);
    $quote_item->save();
}