Event Dispatcher.

Controller

public function indexAction(Request $request)
    {
	    $em = $this->getDoctrine()->getManager();
	    $shipment = new Shipment();
	    $form = $this->createFormBuilder($shipment)
		    ->add('name', TextType::class)
		    ->getForm();
	    $form->handleRequest($request);

	    if ($form->isSubmitted() && $form->isValid()) {
	    	$data = $form->getData();
		    $shipment->setName($data->getName());

		    $dispatcher = $this->get('event_dispatcher');
		    $dispatcher->dispatch('generate.shipment', new GeneratePriceEvent());

			$em->persist($shipment);
			$em->flush();
	    }

        return $this->render(
            'MainBundle:Customer/page:test.html.twig',
            [
				'form' => $form->createView(),
            ]
        );
    }

Event

namespace MainBundle\Event;

use MainBundle\Entity\Price;
use Symfony\Component\EventDispatcher\Event;

class GeneratePriceEvent extends Event
{

	public function generate($value, $discount = null, $em)
	{
		$price = new Price();
		$price->setValue($value);
		$price->setDiscount($discount);
		$em->persist($price);
		$em->flush();
	}
}

Event handler

namespace MainBundle\Event;

use Doctrine\ORM\EntityManager;

class Generate
{
	protected $em;

	public function __construct(EntityManager $em)
	{
		$this->em = $em;
	}

	public function onCreateShipmentEvent(GeneratePriceEvent $event)
	{
		$event->generate(10, 20, $this->em);
	}
}

Service

app.test_listener:
        class: MainBundle\Event\Generate
        arguments: ["@doctrine.orm.entity_manager"]
        tags:
            - { name: kernel.event_listener, event: generate.shipment, method: onCreateShipmentEvent }