Symfony: ParamConverter usage example

AbstractBySlugAndActiveSearcher.php

<?php

namespace FrontEndBundle\Request\ParamConverter;

use Doctrine\Bundle\DoctrineBundle\Registry;
use Doctrine\Common\Persistence\ObjectRepository;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\ParamConverter;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;

abstract class AbstractBySlugAndActiveSearcher
{
    /**
     * @param ParamConverter $configuration
     * @param Registry|null $registry
     *
     * @return bool
     */
    final protected function isObjectSupported(ParamConverter $configuration, Registry $registry = null)
    {
        if ($configuration->getConverter() !== $this->getConverterName()) {
            return false;
        }

        if (!$this->isEntityManagerFound($registry)) {
            return false;
        }

        $className = $configuration->getClass();

        if ($className === null) {
            return false;
        }

        $em = $registry->getManagerForClass($className);

        if ($em->getClassMetadata($className)->getName() !== $this->getEntityClassName()) {
            return false;
        }

        return true;
    }

    /**
     * @param Registry|null $registry
     *
     * @return bool
     */
    private function isEntityManagerFound(Registry $registry = null)
    {
        return null !== $registry && count($registry->getManagers()) > 0;
    }

    /**
     * @param ObjectRepository $repository
     * @param string $slug
     *
     * @return object
     *
     * @throws NotFoundHttpException
     */
    protected function getEntity(ObjectRepository $repository, $slug)
    {
        $entity = $repository->findOneBy([
            'slug' => $slug,
            'active' => true,
        ]);

        if ($entity === null) {
            throw new NotFoundHttpException();
        }

        return $entity;
    }

    /**
     * @return string
     */
    abstract protected function getEntityClassName();

    /**
     * @return string
     */
    abstract protected function getConverterName();
}

CatalogCategoryParamConverter.php

<?php

namespace FrontEndBundle\Request\ParamConverter;

use Doctrine\Bundle\DoctrineBundle\Registry;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\ParamConverter;
use Sensio\Bundle\FrameworkExtraBundle\Request\ParamConverter\ParamConverterInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
use AppBundle\Entity\Category;

class CatalogCategoryParamConverter extends AbstractBySlugAndActiveSearcher implements ParamConverterInterface
{
    /**
     * @var Registry
     */
    protected $registry;


    /**
     * CatalogCategoryParamConverter constructor.
     *
     * @param Registry|null $registry
     */
    public function __construct(Registry $registry = null)
    {
        $this->registry = $registry;
    }

    /**
     * {@inheritdoc}
     */
    public function apply(Request $request, ParamConverter $configuration)
    {
        $categorySlug = $request->attributes->get('categorySlug');

        if ($categorySlug === null) {
            throw new NotFoundHttpException();
        }

        $repository = $this->registry
            ->getManagerForClass($configuration->getClass())
            ->getRepository($configuration->getClass());

        $request->attributes->set($configuration->getName(), $this->getEntity($repository, $categorySlug));
    }

    /**
     * {@inheritdoc}
     */
    public function supports(ParamConverter $configuration)
    {
        return $this->isObjectSupported($configuration, $this->registry);
    }

    /**
     * {@inheritdoc}
     */
    protected function getEntityClassName()
    {
        return Category::class;
    }

    /**
     * {@inheritdoc}
     */
    protected function getConverterName()
    {
        return 'catalog_category_converter';
    }
}

CatalogController.php

<?php

namespace FrontEndBundle\Controller;

use Sensio\Bundle\FrameworkExtraBundle\Configuration\ParamConverter;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;
use AppBundle\Entity\Category;

class CatalogController extends Controller
{
    /**
     * @ParamConverter("category", class="AppBundle:Category", converter="catalog_category_converter")
     *
     * @param Request $request
     * @param Category $category
     *
     * @return \Symfony\Component\HttpFoundation\Response
     */
    public function indexAction(Request $request, Category $category)
    {
        // ...
    }
}

services.yml

# Param Converters
frontend.param_converter.catalog_category_converter:
    class: FrontEndBundle\Request\ParamConverter\CatalogCategoryParamConverter
    arguments:
        - '@doctrine'
    tags:
        - { name: request.param_converter, converter: catalog_category_converter }

https://symfony.com/doc/current/controller/value_resolver.html#adding-a-custom-value-resolver