Php – Magento – Custom attribute in customer address, not copied to sales_flat_order_address and sales_flat_quote_address on checkout

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

Order entities are awkwardly not like normal entities, they use a flat table instead of EAV, which means that it's not enough to just assign an attribute. You must alter the flat table (which I tried here) or create additional tables then join them to the flat table. With hindsight I see I should have taken the second option, it's safer.

I've been looking a bit closer at the order template and there might a hackish sort of workaround via a lesser used block. To start with let's make changes in a layout/local.xml file so it's safe from overwriting by upgrades;

<layout>
    <adminhtml_sales_order_create_index>
        <reference name="gift_options">
            <block type="adminhtml/template" template="YOUR/TEMPLATE.phtml" />
        </reference>
    </adminhtml_sales_order_create_index>
</layout>

The gift options block is constructed in an open-ended way so adding to it is relatively easy. Obviously replace YOUR/TEMPLATE.phtml with the path of a file you will create. The template being inserted needs to have input fields with names like order[testattr] and those should be copied directly to the database table (according to Mage_Adminhtml_Model_Sales_Order_Create, if I am reading the source code right). The gift options block already creates a <fieldset> inside the order's <form> so only the input fields are needed.