Magento 2 extension attributes

Question

I'm a bit lost regarding the Magento 2 extension attributes. It's clear they offer a flexible way to extend the API/interfaces with your own attributes, but what I don't get is how to save the value to a custom database. If I look at the documentation at http://devdocs.magento.com/guides/v2.0/extension-dev-guide/attributes.html it would seem like an automatic system is in place to automatically join your data, but it doesn't work. What am I missing to actually save and get the values?

I'm trying to add a new attribute to shipmentItems's. My extension_attributes.xml:

<?xml version="1.0" encoding="UTF-8"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
    <extension_attributes for="\Magento\Sales\Model\Order\Shipment\Item">
        <attribute code="imei_codes" type="string">
            <join reference_table="custom_shipment_item" reference_field="item_id" join_on_field="shipment_item_id">
                <field>imei_codes</field>
            </join>
        </attribute>
    </extension_attributes>
</config>

Next in my code I'm saving the custom attribute like this:

$extensionAttributes = $shipmentItem->getExtensionAttributes();
$extensionAttributes->setImeiCodes($imeiCodes[$orderItem->getId()]);
$shipmentItem->setExtensionAttributes($extensionAttributes);
$shipmentItem->save();

My custom database gets installed like this:

$table = $installer->getConnection()
    ->newTable($installer->getTable('custom_shipment_item'))
    ->addColumn(
        'shipment_item_id',
         Table::TYPE_INTEGER,
         null,
         ['primary' => true, 'identity' => true, 'nullable' => false],
         'Primary ID of table'
     )
     ->addColumn(
         'imei_codes',
         Table::TYPE_TEXT,
         null,
         ['nullable' => true],
         'IMEI Codes'
     )
     ->setComment('Custom Extended Shipment item Table');

$installer->getConnection()->createTable($table);

The table is properly installed, but the data is not saved automatically to this table. What do I need in order to have this working? Is this the way to go to save some attribute related to shipment items?

Thank you very mucht for you assistance!

Answer 1

Currently, extension attributes are only about Web API. You need to save extension attributes manually using plugins on appropriate services.