Adding a new field to API calls (Extension Attributes)

For adding a new field to the API call as an extension attribute we need to create a Plugin

Firstly Create extension_attributes.xml inside the etc for your module

<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="request_quote_id" type="string" />
    </extension_attributes>
</config>

here I’m adding a request quote id field to the sales order table.

Create a webapi_rest folder and di.xml to initialize the plugin

webapi_rest/di.xml

<?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="orderInformationUpdate" type="JJ\Order\Plugin\Api\OrderRepository" />
    </type>
</config>

now create a Plugin folder inside the module

Plugin/Api/File_name.php

here i created a order repository file

<?php

namespace JJ\Order\Plugin\Api;

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


class OrderRepository
{

    const REQUEST_QUOTE_ID = 'request_quote_id';

    /**
     * Order Extension Attributes Factory
     *
     * @var OrderExtensionFactory
     */
    protected $extensionFactory;

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

    /**
     * Add "delivery_type" extension attribute to order data object to make it accessible in API data
     *
     * @param OrderRepositoryInterface $subject
     * @param OrderInterface $order
     *
     * @return OrderInterface
     */
    public function afterGet(OrderRepositoryInterface $subject, OrderInterface $order)
    {
        $deliveryType = $order->getData(self::REQUEST_QUOTE_ID);
        $extensionAttributes = $order->getExtensionAttributes();
        $extensionAttributes = $extensionAttributes ? $extensionAttributes : $this->extensionFactory->create();
        $extensionAttributes->setRequestQuoteId($deliveryType);
        $order->setExtensionAttributes($extensionAttributes);
        return $order;
    }

    /**
     * Add "delivery_type" extension attribute to order data object to make it accessible in API data
     *
     * @param OrderRepositoryInterface $subject
     * @param OrderSearchResultInterface $searchResult
     *
     * @return OrderSearchResultInterface
     */
    public function afterGetList(OrderRepositoryInterface $subject, OrderSearchResultInterface $searchResult)
    {
        $orders = $searchResult->getItems();

        foreach ($orders as &$order) {
            $deliveryType = $order->getData(self::REQUEST_QUOTE_ID);
            $extensionAttributes = $order->getExtensionAttributes();
            $extensionAttributes = $extensionAttributes ? $extensionAttributes : $this->extensionFactory->create();
            $extensionAttributes->setRequestQuoteId($deliveryType);
            $order->setExtensionAttributes($extensionAttributes);
        }

        return $searchResult;
    }
}