Magento: Adding a custom EAV attribute that autopopulates with its default value on entity creation

Is there a way to add a custom EAV attribute that automatically gets set to its default value upon creation of a new entity?

I set eav_attribute.is_required to 1 and eav_attribute.default_value to 0 (the default value), but it's not setting the attribute automatically when I create a new object.

By the way, the EAV entity type is shipment. I'm working on an installation of 1.3.2.4, before sales data was stored in flat tables.

EDIT

Jonathan Day asked "how are you adding the attribute?"

In ModuleDir\sql\module_setup\mysql4-install-0.1.0.php, I have the following code:

$eav = new Mage_Eav_Model_Entity_Setup('sa开发者_如何学编程les_setup');
$eav->addAttribute('shipment', 'fieldname', array('type' => 'int'));

I also have the this code for later versions of Magento (after the sales entities went from EAV to flat tables):

$w = $this->_conn;
$table = $this->getTable('sales_flat_shipment');
$w->addColumn($table, 'fieldname', 'int');
$w->addKey($table, 'fieldname', 'fieldname', 'index');

Jonathan Day asked "Have you checked that the attribute is added to eav_attribute with the correct fields?"

Yes, it has been added to eav_attribute. And the attribute is settable and gettable.

If you look at Varien_Object::getData() (in /lib/Varien/Object.php) you can see the following line:

$default = null;

...and any instance of missing data returns $default. So the default value you set in your attribute is being ignored.

Since any undefined 'get' is handled by getData() it means a null will always be the default. It seems the only option is to override Sales_Model_Order_Shipment (or whichever entity model it is) and provide custom getters.

A simple example would be:

function getSample()
{
    if (!$this->hasSample())
        return 0;

    return $this->getData('sample');
}