Example

KernelEventsSubscriber.php

<?php

class KernelEventsSubscriber {
    
    public function flushChanges()
    {
        $this->em->flush();
    }
    
    public function prepareResponse(GetResponseForControllerResultEvent $event)
    {
        $this->flushChanges();
        
        return $event->setResponse(
            // status code and headers should be provided from annotations or configs...
            new Response($this->serializer->serialize($event->getResponse()), 200, [
                'Content-type': 'application/json'
            ]);
        );
    }
    
    // ...
    
}

RegistrationService.php

<?php

class RegistrationService
{
    
    private $validator;
    
    private $repository;
    
    public function __construct(UserRepository $repository, Validator $validator)
    {
        $this->validator = $validator;
        $this->repository = $repository;
    }
    
    public function registerUser($email, $password)
    {
        $user = new User($email, $password);
        if (!$this->validator->isValid($user)) {
            throw new \DomainException();
        }
        
        $this->repository->add($user);
        
        return $user;
    }
}

UserController.php

<?php

class UserController extends Controller {
    
    public function registerAction(Request $request)
    {
        $user = $this
            ->get('app.user.registrator')
            ->registerUser(
                $request->get('email'),
                $request->get('password')
            );
            
        return $user;
    }
    
}

UserRepository.php

<?php

class UserRepository
{
    
    public function __construct(EntityManagerInterface $em)
    {
        $this->em = $em;
    }
    
    public function add(User $user)
    {
        $this->em->persist($user);
    }
    
    public function remove(User $user)
    {
        $this->em->remove($user);
    }
}