Drupal 8 Param Converters (Drupal 7 Auto Loaders)

autoloader_example_d7.module

<?php

/**
 * Implements hook_menu().
 */
function autoloader_example_d7_menu() {
  $items = array();

  $items['example/%autoloader_example_d7'] = array(
    'title' => t('Autoload example data'),
    'access callback' => 1,
    'page callback' => 'autoloader_example_d7_page',
    'page arguments' => array(1),
  );

  return $items;
}

/**
 * load example object
 */
function autoloader_example_d7_load($id) {
  return db_query('SELECT * FROM {autoloader_example_d7} WHERE id = :id', array(':id' => $id))->fetch();
}

/**
 * display page
 */
function autoloader_example_d7_page($data) {
  return t('Example object %id %title loaded', array('%id' => $data->id, '%title' => $data->title));
}

autoloader_example_d8.routing.yml

autoloader_example_d8.example_view:
  path: '/example/{autoloader_example_d8}'
  defaults:
    _content: '\Drupal\autoloader_example_d8\Controller\ExampleController::page'
    _title_callback: '\Drupal\autoloader_example_d8\Controller\ExampleController::pageTitle'
  requirements:
    _access: 1
  options:
    parameters:
      autoloader_example_d8:
        type: autoloader_example_d8
        loader: TRUE

autoloader_example_d8.services.yml

services:
  paramconverter.autoloader_example_d8:
    class: Drupal\autoloader_example_d8\ParamConverter\ExampleConverter
    arguments: ['@entity.manager']
    tags:
      - { name: paramconverter, priority: 10 }

ExampleController.php

<?php

/**
 * @file
 * Contains \Drupal\autoloader_example_d8\Controller\ExampleController.
 */

namespace Drupal\autoloader_example_d8\Controller;

use Drupal\Component\Utility\String;
use Drupal\Core\Controller\ControllerBase;
use Drupal\Core\Entity\EntityInterface;
use Symfony\Component\HttpFoundation\Response;

/**
 * Returns responses for Transaction routes.
 */
class ExampleController extends ControllerBase {

  /**
   * @param Drupal\mcapi\TransactionInterface $transaction
   *  The Transaction that we are displaying.
   *
   * @return array
   *  An array suitable for drupal_render().
   */
  public function page($autoloader_example_d8) {
    return t('Example object %id %title loaded', array('%id' => $autoloader_example_d8->id, '%title' => $autoloader_example_d8->title));
  }

  /**
   * The _title_callback for the node.view route.
   *
   * @param NodeInterface $transaction
   *   The current node.
   *
   * @return string
   *   The page title.
   */
  public function pageTitle($autoloader_example_d8) {
    return String::checkPlain($autoloader_example_d8->label());
  }
}

ExampleConverter.php

<?php

/**
 * @file
 * Contains \Drupal\autoloader_example_d8\ParamConverter\ExampleConverter.
 */

namespace Drupal\autoloader_example_d8\ParamConverter;

use Drupal\Core\Entity\EntityManager;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Routing\Route;
use Drupal\Core\ParamConverter\ParamConverterInterface;

/**
 * Provides upcasting for a view entity to be used in the Views UI.
 *
 * Example:
 *
 * pattern: '/example/{autoloader_example_d8}'
 * options:
 *   parameters:
 *     autoloader_example_d8:
 *       loader: TRUE
 */
class ExampleConverter extends ParamConverter implements ParamConverterInterface {

  /**
   * {@inheritdoc}
   */
  public function convert($value, $definition, $name, array $defaults, Request $request) {
    $entity_type = substr($definition['type'], strlen('entity:'));
    if ($storage = $this->entityManager->getStorageController($entity_type)) {
      $entity = $storage->loadByProperties(array('id' => $value, 'parent' => '0'));
      if (!empty($entity)) {
        return reset($entity);
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public function applies($definition, $name, Route $route) {
    if (parent::applies($definition, $name, $route)) {
      return !empty($definition['loader']) && $definition['type'] === 'entity:autoloader_example_d8';
    }
    return FALSE;
  }
}