Symfony2 service

I have 2 tables in DB (question and answer). One question has many answers.

I get some Answers and depends on question.type I prepare results array.

In app without any framework I have Factory class which return specific object (SingleChoiceQuestion, OpenQuestion, MultipleChoiceQuestion) depends question.type from DB. All Questions extends abstract class Question which has declared abstract method getResults. All types have their own business logic to prepare results.

So in this situation when I have created object by factory I'm using method getResults and everything works well.

I would like to create it in Symfony and I read documentation. In my opinion I should create services for all my Question types.

I have created AggregatedResultsManager with method generate which returns results array. Depends on question.type it calls getResults method from specific service.

I would like to add, that I can't change DB structure.

My questions:

1. Am I creating and using services right? If I do it wrong, please help me understanding it and show me the right way.
2. I will have several services like AggregatedResultsManager and about 18 Question types.

In each service I will need to create switch with 18 choices, how to prevent that?

switch ($this->question->getType()) {
    case Question::SINGLE:
        $results = $this->container->get('app.single_choice_question')->getResults($answers);
        break;
    // other types
}

I have some idea to create array with types and service names:

$services = [
    Question::SINGLE => 'app.single_choice_question',
    Question::MULTIPLE => 'app.multiple_choice_question',
    Question::OPEN => 'app.open_question',
];

and then use it in each service like that:

$results = $this->container->get($services[$this->question->getType()])->getResults($answers);

I think it's the best way to not use switch with 18 choices. But I will need to hardcode service names in array.

My code:

services.yml

app.question:
    class: AppBundle\Questions\Question
    abstract: true
    arguments: ['@doctrine.orm.entity_manager']

app.single_choice_question:
    class: AppBundle\Questions\SingleChoice
    parent: app.question

app.agreggated_results_manager:
    class:  AppBundle\Results\AggregatedResultsManager
    arguments: ['@doctrine.orm.entity_manager', '@service_container']

abstract Question

abstract class Question
{
    /**
     * @var EntityManager
     */
    protected $em;

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

    abstract public function getResults($answers);
}

SingleChoice

class SingleChoice extends Question
{
    public function getResults($answers)
    {
        $results = [];

        // business logic

        return $results;
    }
}

Results

class AggregatedResultsManager
{
    /**
     * @var EntityManager
     */
    private $em;

    /**
     * @var Question
     */
    private $question;

    /**
     * @var ContainerInterface
     */
    private $container;

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

    public function generate()
    {
        if (!$this->question) {
            throw new \LogicException('Question is not set');
        }

        $answers = $this->em
            ->getRepository('AppBundle:Answer')
            ->findBy(['question' => $this->question]);

        $results = [];

        if (empty($answers)) {
            return $results;
        }

        switch ($this->question->getType()) {
            case Question::SINGLE:
                $results = $this->container->get('app.single_choice_question')->getResults($answers);
                break;
            // other types
        }

        return $results;
    }


    public function setQuestion(Question $question)
    {
        $this->question = $question;
    }
}

Controller

public function questionIdsAction(Question $question)
{
    $resultsManager = $this->get('app.agreggated_results_manager');
    $resultsManager->setQuestion($question);
    $results = $resultsManager->generate();

    return new JsonResponse($results);
}