Transferring a bespoke Customer Address attribute to the Customer Address Data layer

Question

I've added a static Customer Address attribute (for some reason, other didn't work, but whatever; another time):

$setup->addAttribute('customer_address', 'xxx', [
    'type' => 'static',
    'input' => 'text',
    'label' => 'XXX',
    'global' => 1,
    'visible' => 1,
    'required' => 0,
    'user_defined' => 1,
    'visible_on_front' => 1,
    'group' => 'General',
    // 'used_in_forms' => ['adminhtml_customer']
    'used_in_forms' => ['adminhtml_customer_address']
]);

The attribute is showing up in the admin panel and, on load, the object is populated with the correct value.

But now I want to make sure this attribute gets correctly transferred to the Data model as well (\Magento\Customer\Api\Data\AddressInterface):

$x = \Magento\Framework\App\ObjectManager::getInstance()
       ->get(\Magento\Customer\Api\AddressRepositoryInterface::class);

/** @var \Magento\Customer\Api\Data\AddressInterface $addr */
$addr = $x->getById(1); // <-- "xxx" is not available here; others are

At first, I thought that only by having the static attribute, M2 would transfer its value to the Data model, or at least to its getCustomAttributes() or getExtensionAttribute(). It didn't. So I've created an extension_attrbutes.xml, telling it to do so:

<?xml version="1.0"?>
<config path="to.xsd">
    <extension_attributes for="Magento\Customer\Api\Data\AddressInterface">
        <attribute code="xxx" type="string" />
    </extension_attributes>
</config>

Damn it, that didn't work either, because I didn't specify a join directive and thus failing some conditions. But do I have to specify a join condition when my attribute is static/column? Furthermore, the Address Data interface is implemented (not auto-generated) so I think the only way is through extension attributes, right?

Do I really have to do it manually?

I'm really starting to hate those Data layers. There's not only many criterias to get an attribute functioning correctly, but, once you finally have made a valid attribute, some other find-them-if-you-can criteria need to be satisfied in order to have attributes into the Data layer.

Answer 1

Regarding saving/loading extension attribute

In general. The only correct way to make new attribute available in your data model is to populate it using plugin. The same relates to save, if you want have it saved to DB. For customer address you need "before" plugin for \Magento\Customer\Api\AddressRepositoryInterface::save() and "after" plugin for \Magento\Customer\Api\AddressRepositoryInterface::getById(). In that plugin you, as extension developer, know where your extension attribute is stored (may be anywhere, another table for example) and how it should be saved/retrieved.

In your particular case. This extension attribute can be loaded/saved using \Magento\Customer\Model\Address in plugins.

Is there a reason not to create new system EAV attribute? Then it will automatically be available in getCustomAttributes() array, and no need to deal with plugins.

Regarding other points in your question

Join directives are necessary only if you want to make this attribute available in the list of addresses, also you might want to declare them if there is a need to perform filtration by this attribute while using \Magento\Customer\Api\AddressRepositoryInterface::getList().

getCustomAttributes() will only return you EAV attributes.

Hopefully, you will love service contracts when your custom module will not be broken after the next releases of Magento 2 (of course if you do not bypass service contracts and use models/collections/resource models directly). And when you start consuming/exposing Magento 2 web API, which is now based on the same service contracts. So you have to make changes only in one place (e.g. via plugin) and they will be applied everywhere. This was impossible in Magento 1.