How to get the custom order attributes in default order Api response in magento 2.3

Question

I have created a new custom order attribute named delivery_date and shown the same in sales order grid but i am not getting the custom attribute in my order Api response.

The error I am getting is Fatal error: Uncaught Error: Call to undefined method

Magento\Sales\Api\Data\OrderExtension::setTipAndTrickAttribute() 

Please help.

app/code/Amos/CustomOrder/etc/di.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © 2013-2017 Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/ObjectManager/etc/config.xsd">
 <virtualType name="Magento\Sales\Model\ResourceModel\Order\Grid" type="Magento\Sales\Model\ResourceModel\Grid">
 <arguments>
 <argument name="columns" xsi:type="array">
 <item name="delivery_date" xsi:type="string">sales_order.delivery_date</item>
 <item name="no_of_days" xsi:type="string">sales_order.no_of_days</item>
 <item name="no_of_crew" xsi:type="string">sales_order.no_of_crew</item>
 </argument>
 </arguments>
 </virtualType> 
</config>

app/code/Amos/CustomOrder/etc/events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
<event name="sales_order_load_after">
 <observer name="sales_order_load_delivery_date" instance="Magestore\TipAndTrick\Observer\Sales\OrderLoadAfter" />
</event>
</config>

Amos/CustomOrder/etc/extension_attributes.xml

<?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="delivery_date" type="string" />
</extension_attributes>
</config> 

Amos/CustomOrder/Observer/Sales/OrderLoadAfter.php

<?php
namespace Amos\CustomOrder\Observer\Sales;
use Magento\Framework\Event\ObserverInterface;
class OrderLoadAfter implements ObserverInterface
{
public function execute(\Magento\Framework\Event\Observer $observer)
{
 $order = $observer->getOrder();
 $extensionAttributes = $order->getExtensionAttributes();
 if ($extensionAttributes === null) {
 $extensionAttributes = $this->getOrderExtensionDependency();
 }
 $attr = $order->getData('delivery_date');
 $extensionAttributes->setTipAndTrickAttribute($attr);
 $order->setExtensionAttributes($extensionAttributes);
}
private function getOrderExtensionDependency()
{
 $orderExtension = \Magento\Framework\App\ObjectManager::getInstance()->get(
 '\Magento\Sales\Api\Data\OrderExtension'
 );
 return $orderExtension;
}
}

• Ramkishan Suthar: Hi Meetali, welcome to Magento SE, Please clear generated/ folder or try with di:compile
• Ramkishan Suthar: One more thing you are calling wrong method it should be setDeliveryDate() not setTipAndTrickAttribute()
• Flying Finner: Hi Ramkishan, thank you for the response. Now the error of wrong method is resolved but still i did'nt got the delivery_date attribute in my Api response.
• Ramkishan Suthar: I guess, setting extension attribute value in observer won't work you should try plugin instead of observer.