Magento: save custom address attribute in checkout

Question

This is what i did in my website: Admin->Customers->Attributes->Manage Customer Address Attributes and add a new attribute , the user can see it in his/her profile,

Answer 1

After looking in the Magento's code and reading the wiki, I was able to complete it, my new attribute was saved in the address edit form in the profile, but was not saved when I enter it in the checkout form, that was because I need to override some Magento core files, the first step was adding the new attribute to app\code\core\Mage\Customer\etc\config.xml, I copied to app\code\core\Mycompany\Customer\etc\config.xml, as my new attribute code is rfc, I located the <fieldsets> entry and

<customer_dataflow>
    ....
    <rfc><billing>1</billing><shipping>1</shipping></rfc>
</customer_dataflow>

now I need to add the new attribute to the app\code\core\Mage\Customer\Model\Entity\Setup.php i did the same to override, copied to my local namespace, and in the function getDefaultEntities() i locate the

'customer_address'=>array(
    ....
            'rfc' => array(
            'label'         => 'RFC',
            'required'      => false,
            'sort_order'    => 135,
    ),
)  

now, I need to do also the same in app\code\core\Mage\Sales\etc\config.xml, but now should look like this

<sales_copy_order_billing_address>
    .....
    <rfc><to_order>*</to_order></rfc>
</sales_copy_order_billing_address>

<sales_copy_order_shipping_address>
    ......
    <rfc><to_order>*</to_order></rfc>
</sales_copy_order_shipping_address>

<sales_convert_quote_address>
    ........
    <rfc><to_order_address>*</to_order_address><to_customer_address>*</to_customer_address></rfc>
</sales_convert_quote_address>

<sales_convert_order_address>
    .........
    <rfc><to_quote_address>*</to_quote_address></rfc>
</sales_convert_order_address>

<customer_address>
    .......
    <rfc><to_quote_address>*</to_quote_address></rfc>
</customer_address>

Hope it can help someone else