Magento 2: How to get order data in observer on success page

Question

I'm here domain.com/checkout/onepage/success/

Calling my observer on checkout_onepage_controller_success_action

$order = $observer->getEvent()->getOrder();
echo $order->getCustomerId()
echo $order->getState()

I'm not able to get all information above. How to get?

It gives

Fatal error: Call to a member function getState() on null

Answer 1

checkout_onepage_controller_success_action give you order id's

by using $observer->getEvent()->getOrderIds().

This does not given order object directly so, you are getting the error

Then you need to object by this id

<?php
namespace [VendorName]\[ModuleName]\Observer;

use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\App\Request\DataPersistorInterface;
use Magento\Framework\App\ObjectManager;

class [ClassName] implements ObserverInterface
{
    protected $_order;
    public function __construct(
        \Magento\Sales\Api\Data\OrderInterface $order
    ) {
         $this->_order = $order;    
    }

    /**
     *
     * @param \Magento\Framework\Event\Observer $observer
     * @return void
     */
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
      $orderids = $observer->getEvent()->getOrderIds();

        foreach($orderids as $orderid){
            $order = $this->_order->load($orderid);
        }
    }

}

Answer 2

Create events.xml at app/code/VendoreName/ModuleName/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="checkout_onepage_controller_success_action">
        <observer name="checkout_controller_success_action" instance="VendoreName\ModuleName\Observer\AfterPlaceOrder"  />
    </event>
</config>

Create Observer file at app/code/VendoreName/ModuleName/Observer/AfterPlaceOrder.php

namespace VendoreName\ModuleName\Observer;

use Magento\Framework\Event\ObserverInterface;

class AfterPlaceOrder implements ObserverInterface
{
    /**
     * Order Model
     *
     * @var \Magento\Sales\Model\Order $order
     */
    protected $order;

     public function __construct(
        \Magento\Sales\Model\Order $order
    )
    {
        $this->order = $order;
    }

    public function execute(\Magento\Framework\Event\Observer $observer)
    {
       $orderId = $observer->getEvent()->getOrderIds();
        $order = $this->order->load($orderId);

        //get Order All Item
        $itemCollection = $order->getItemsCollection();
        $customer = $order->getCustomerId(); // using this id you can get customer name
    }
}

Answer 3

In Magento 2.1.9 this works for me.

etc/frontend/events.xml

<event name="checkout_onepage_controller_success_action">
    <observer instance="Vendor\Module\Observer\Checkout\OnepageControllerSuccessAction" name="vendor_module_observer_checkout_onepagecontrollersuccessaction_checkout_onepage_controller_success_action"/>
</event>

Observer\Checkout\OnepageControllerSuccessAction.php

<?php

namespace Vendor\Module\Observer\Checkout;

class OnepageControllerSuccessAction implements \Magento\Framework\Event\ObserverInterface
{

    public function __construct(\Magento\Sales\Model\Order $order)
    {
        $this->order = $order;
    }

    /**
     * Execute observer
     *
     * @param \Magento\Framework\Event\Observer $observer
     * @return void
     */
    public function execute(\Magento\Framework\Event\Observer $observer)
    {

        $orderids = $observer->getEvent()->getOrderIds();

        try {
            foreach ($orderids as $orderid) {
                $order = $this->order->load($orderid);                    
                $order->hold();
                $order->save();
            }
        } catch (\Magento\Framework\Exception\LocalizedException $e) {
            // Error logic
        } catch (\Exception $e) {
            // Generic error logic
        }
    }
}

I didn't add the logic why the order is placed on hold, but this will get you close to how to modify each of the current orders and saving them.