Magento2 添加 Extension Attributes

<?xml version="1.0"?>
<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\Api\Data\OrderInterface">
        <attribute code="test_code" type="string" />
    </extension_attributes>
</config>

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
  <type name="Magento\Sales\Api\OrderRepositoryInterface">
    <plugin name="test_order_plugin" type="Package\Module\Plugin\Model\Sales\OrderPlugin" />
  </type>
</config>

<?php

namespace Package\Module\Plugin\Model\Sales;

use Magento\Sales\Api\Data\OrderExtensionFactory;
use Magento\Sales\Api\OrderRepositoryInterface;
use Magento\Sales\Api\Data\OrderInterface;
use Magento\Sales\Api\Data\OrderExtension;

class OrderPlugin
{
    /**
     * @var OrderExtensionFactory
     */
    private $orderExtensionFactory;

    /**
     * @param OrderExtensionFactory $orderExtensionFactory
     */
    public function __construct(
        OrderExtensionFactory $orderExtensionFactory
    ) {
        $this->orderExtensionFactory = $orderExtensionFactory;
    }

    /**
     * Get reward points
     *
     * @param OrderRepositoryInterface $subject
     * @param OrderInterface $resultOrder
     * @return OrderInterface
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     */
    public function afterGet(OrderRepositoryInterface $subject, OrderInterface $resultOrder)
    {
        $extensionAttributes = $resultOrder->getExtensionAttributes();

        /** @var OrderExtension $orderExtension */
        $orderExtension = $extensionAttributes
            ? $extensionAttributes
            : $this->orderExtensionFactory->create();

        $orderExtension->setTestCode($resultOrder->getTestCode());
       
        $resultOrder->setExtensionAttributes($orderExtension);

        return $resultOrder;
    }
}