Add new customer attribute onepage Magento checkout

In this example I’m going to explain how to add a new customer attribute and collect the data from the checkout attribute or register form.
Remember to activate the Vat/Tax attribute for the checkout, check right image
The new attribute will be a TaxVat Document Type Info, so using the TaxVat attribute of Magento you could collect the kind of document: Passport, NIT, NIF, Cedula, DNI…

1. Add the new customer attribute to the database. Also create a new column to save the attribute when in the quote. (This allows you to keep the value through the onepage checkout page steps).
Execute this code in any .phtml file or any file that you could run under Magento classes.

//Attribute to add
$newAttributeName = "taxvattype"; //modify this with the name of your attribute

//a) Add EAV Attributes (modify as you needed)
$attribute  = array(
	'type'			=> 'varchar',
	'label'			=> 'Tax/VAT Type',
	'visible'		=> true,
	'required'		=> false,
	'user_defined'	=> false,
	'searchable'	=> false,
	'filterable'	=> false,
	'comparable'	=> false,
);

$setup = new Mage_Eav_Model_Entity_Setup('core_setup');
//Add to customer
$setup->addAttribute('customer', $newAttributeName, $attribute);

//b) Add Quote attributes (one page step to step save field)
$setup = new Mage_Sales_Model_Mysql4_Setup('sales_setup');
$setup->getConnection()->addColumn(
        $setup->getTable('sales_flat_quote'),
        $newAttributeName,
        'text NULL DEFAULT NULL'
    );
$setup->addAttribute('quote', "customer_".$newAttributeName, array('type' => 'static', 'visible' => false));

2. Add a new line to the file
/app/code/core/Mage/Customer/etc/config.xml

    <global>
        <fieldsets>
            <customer_account>
                <prefix><create>1</create><update>1</update><name>1</name></prefix>
                <firstname><create>1</create><update>1</update><name>1</name></firstname>
                <middlename><create>1</create><update>1</update><name>1</name></middlename>
                <lastname><create>1</create><update>1</update><name>1</name></lastname>
                <suffix><create>1</create><update>1</update><name>1</name></suffix>
                <email><create>1</create><update>1</update></email>
                <password><create>1</create></password>
                <confirmation><create>1</create></confirmation>
                <dob><create>1</create><update>1</update></dob>
                <taxvat><create>1</create><update>1</update></taxvat>
                <taxvattype><create>1</create><update>1</update></taxvattype>
                <gender><create>1</create><update>1</update></gender>

3. Modify your checkout template
/app/design/frontend/your_template/default/template/checkout/onepage/billing.phtml

        <?php $_taxvat = $this->getLayout()->createBlock('customer/widget_taxvat') ?>
        <?php if ($_taxvat->isEnabled()): ?>
        		<li>
                    <div class="field">
                        <label for="billing:taxvattype"><?php echo $this->__('Tax/VAT Document Type') ?></label>
                        <div class="input-box">
                            <input type="text" title="<?php echo $this->__('Tax/VAT Document Type') ?>" name="billing[taxvattype]" id="billing:taxvattype" value="<?php echo $this->htmlEscape($this->getData("taxvattype")); ?>" class="input-text" />
                        </div>
                    </div>
                </li>
                <li>
                    <?php echo $_taxvat->setTaxvat($this->getQuote()->getCustomerTaxvat())->setFieldIdFormat('billing:%s')->setFieldNameFormat('billing[%s]')->toHtml() ?>
                </li>
        <?php endif ?>

4. Modify the register form template
/app/design/frontend/your_template/default/template/customer/form/register.phtml

            <?php if ($_taxvat->isEnabled()): ?>
				    <div class="input-box">
				        <label for="taxvat_type"><?php echo $this->__('Tax/VAT Document Type') ?></label><br/>
				        <input type="text" name="taxvattype" id="taxvattype" value="<?php echo $this->htmlEscape($this->getData("taxvattype")); ?>" title="<?php echo $this->__('Tax/VAT Document Type') ?>" class="input-text" />
				    </div>
                <li><?php echo $_taxvat->setTaxvat($this->getFormData()->getTaxvat())->toHtml() ?></li>
            <?php endif ?>

5. Modify the file
/app/code/core/Mage/Checkout/Model/Type/Onepage.php (Please remember to overrite with a module instead).
a) Function saveBilling($data, $customerAddressId)

        if (empty($data)) {
            return array('error' => -1, 'message' => $this->_helper->__('Invalid data.'));
        }

        $address = $this->getQuote()->getBillingAddress();

$this->getQuote()->setData("customer_taxvattype",$data['taxvattype']);

        if (!empty($customerAddressId)) {
            $customerAddress = Mage::getModel('customer/address')->load($customerAddressId);
            if ($customerAddress->getId()) {
                if ($customerAddress->getCustomerId() != $this->getQuote()->getCustomerId()) {

b) Function saveOrder()

            default:
                $this->_prepareCustomerQuote();
                break;
        }

	    $billing = $this->getQuote()->getBillingAddress();
	    if ($this->getQuote()->getData("customer_taxvattype") && !$billing->getData("taxvattype")) {
	    	//Save in the customer
	    	$this->getQuote()->getCustomer()->setData("taxvattype", $this->getQuote()->getData("customer_taxvattype"));
		}

        $service = Mage::getModel('sales/service_quote', $this->getQuote());
        $service->submitAll();