Magento2 | Change subject email of new order if condition is true

Question

I created an observer that changes the email subject when I place a new order: This is the ChangeOrderEmailSubject.php file:

<?php
namespace Sales\OrderCust\Observer;

use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\Event\Observer;
use Magento\Sales\Model\Order;

class ChangeOrderEmailSubject implements ObserverInterface
{
    public function execute(Observer $observer)
    {
        /** @var Order $order */
        $order = $observer->getEvent()->getOrder();

        $orderNumber = $order->getIncrementId();
        $customValue = $order->getIdreorder();

        $emailSubject = __("Order N.") . $orderNumber;

        if ($customValue != "") {
            $emailSubject .= " Riordino N.".$customValue;
        }

        /** @var \Magento\Sales\Model\Order\Email\Container $emailContainer */
        $emailContainer = $observer->getEvent()->getContainer();
        $emailContainer->setSubject($emailSubject);
    }
}

Instead, this is the events.xml file:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="sales_order_place_after">
        <observer name="custom_shipping_description" instance="Sales\OrderCust\Observer\CustomShippingDescriptionObserver" method="execute" />
        <observer name="change_order_email_subject" instance="Sales\OrderCust\Observer\ChangeOrderEmailSubject" />
    </event>
</config>

Unfortunately when I try to execute the new order this is the error code I get “main.CRITICAL: Error: Call to a member function setSubject() on null in ”. How can I solve this problem? Maybe “\Magento\Sales\Model\Order\Email\Container” is not the correct method to call to change the subject of the new order email?

Answer 1

You can solve this by as i tested it on my environment works fine

magento/module-sales/Model/Order/Email/Sender/OrderSender.php

in prepareTemplate

protected function prepareTemplate(Order $order)
    {
        $orderNumber = $order->getIncrementId();
        $customValue = 'ssss';
        
        $emailSubject = "Order N. " . $orderNumber;
        
        if ($customValue != "") {
            $emailSubject .= " Riordino N. " . $customValue;
        }

        
        $transport = [
            'order' => $order,
            'order_id' => $order->getId(),
            'billing' => $order->getBillingAddress(),
            'payment_html' => $this->getPaymentHtml($order),
            'store' => $order->getStore(),
            'formattedShippingAddress' => $this->getFormattedShippingAddress($order),
            'formattedBillingAddress' => $this->getFormattedBillingAddress($order),
            'created_at_formatted' => $order->getCreatedAtFormatted(2),
            'order_data' => [
                'customer_name' => $order->getCustomerName(),
                'is_not_virtual' => $order->getIsNotVirtual(),
                'email_customer_note' => $order->getEmailCustomerNote(),
                'frontend_status_label' => $order->getFrontendStatusLabel()
            ],
            'subjects' => $emailSubject  // Add the email subject to the transport array
        ];
        if (empty($customValue)) {
            unset($transport['subjects']);
        }
        $transportObject = new DataObject($transport);

        /**
         * Event argument `transport` is @deprecated. Use `transportObject` instead.
         */
        $this->eventManager->dispatch(
            'email_order_set_template_vars_before',
            ['sender' => $this, 'transport' => $transportObject, 'transportObject' => $transportObject]
        );

        $this->templateContainer->setTemplateVars($transportObject->getData());

        parent::prepareTemplate($order);
    }

and in order email from backend the template you are using use