How to Create a custom Route Loader

What is a Custom Route Loader

A custom route loader enables you to generate routes based on some conventions or patterns. A great example for this use-case is the FOSRestBundle where routes are generated based on the names of the action methods in a controller.

You still need to modify your routing configuration (e.g. app/config/routing.yml) manually, even when using a custom route loader.

Loading Routes

The routes in a Symfony application are loaded by the DelegatingLoader. This loader uses several other loaders (delegates) to load resources of different types, for instance YAML files or @Route annotations in controller files. The specialized loaders implement LoaderInterface and therefore have two important methods: supports() and load().

Take these lines from the routing.yml in the Symfony Standard Edition:

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# app/config/routing.yml
app:
    resource: '@AppBundle/Controller/'
    type:     annotation

When the main loader parses this, it tries all registered delegate loaders and calls their supports() method with the given resource (@AppBundle/Controller/) and type (annotation) as arguments. When one of the loader returns true, its load() method will be called, which should return a RouteCollection containing Route objects.

Loading Routes with a Custom Service

Using a regular Symfony service is the simplest way to load routes in a customized way. It's much easier than creating a full custom route loader, so you should always consider this option first.

To do so, define type: service as the type of the loaded routing resource and configure the service and method to call:

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# app/config/routing.yml
admin_routes:
    resource: 'admin_route_loader:loadRoutes'
    type: service

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<!-- app/config/routing.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<routes xmlns="http://symfony.com/schema/routing"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/routing
        http://symfony.com/schema/routing/routing-1.0.xsd">

    <import resource="admin_route_loader:loadRoutes" type="service"/>
</routes>

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// app/config/routing.php
use Symfony\Component\Routing\RouteCollection;

$routes = new RouteCollection();
$routes->addCollection(
    $loader->import("admin_route_loader:loadRoutes", "service")
);

return $routes;

In this example, the routes are loaded by calling the loadRoutes() method of the service whose ID is admin_route_loader. Your service doesn't have to extend or implement any special class, but the called method must return a RouteCollection object.

Creating a custom Loader

To load routes from some custom source (i.e. from something other than annotations, YAML or XML files), you need to create a custom route loader. This loader has to implement LoaderInterface.

In most cases it is easier to extend from Loader instead of implementing LoaderInterface yourself.

The sample loader below supports loading routing resources with a type of extra. The type name should not clash with other loaders that might support the same type of resource. Just make up a name specific to what you do. The resource name itself is not actually used in the example:

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// src/AppBundle/Routing/ExtraLoader.php
namespace AppBundle\Routing;

use Symfony\Component\Config\Loader\Loader;
use Symfony\Component\Routing\Route;
use Symfony\Component\Routing\RouteCollection;

class ExtraLoader extends Loader
{
    private $isLoaded = false;

    public function load($resource, $type = null)
    {
        if (true === $this->isLoaded) {
            throw new \RuntimeException('Do not add the "extra" loader twice');
        }

        $routes = new RouteCollection();

        // prepare a new route
        $path = '/extra/{parameter}';
        $defaults = array(
            '_controller' => 'AppBundle:Extra:extra',
        );
        $requirements = array(
            'parameter' => '\d+',
        );
        $route = new Route($path, $defaults, $requirements);

        // add the new route to the route collection
        $routeName = 'extraRoute';
        $routes->add($routeName, $route);

        $this->isLoaded = true;

        return $routes;
    }

    public function supports($resource, $type = null)
    {
        return 'extra' === $type;
    }
}

Make sure the controller you specify really exists. In this case you have to create an extraAction() method in the ExtraController of the AppBundle:

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// src/AppBundle/Controller/ExtraController.php
namespace AppBundle\Controller;

use Symfony\Component\HttpFoundation\Response;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;

class ExtraController extends Controller
{
    public function extraAction($parameter)
    {
        return new Response($parameter);
    }
}

Now define a service for the ExtraLoader:

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# app/config/services.yml
services:
    app.routing_loader:
        class: AppBundle\Routing\ExtraLoader
        tags:
            - { name: routing.loader }

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<?xml version="1.0" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="app.routing_loader" class="AppBundle\Routing\ExtraLoader">
            <tag name="routing.loader" />
        </service>
    </services>
</container>

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use AppBundle\Routing\ExtraLoader;

$container
    ->register('app.routing_loader', ExtraLoader::class)
    ->addTag('routing.loader')
;

Notice the tag routing.loader. All services with this tag will be marked as potential route loaders and added as specialized route loaders to the routing.loader service, which is an instance of DelegatingLoader.

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# app/config/routing.yml
app_extra:
    resource: .
    type: extra

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<?xml version="1.0" encoding="UTF-8" ?>
<routes xmlns="http://symfony.com/schema/routing"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/routing
        http://symfony.com/schema/routing/routing-1.0.xsd">

    <import resource="." type="extra" />
</routes>

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// app/config/routing.php
use Symfony\Component\Routing\RouteCollection;

$routes = new RouteCollection();
$routes->addCollection($loader->import('.', 'extra'));

return $routes;

More advanced Loaders

If your custom route loader extends from Loader as shown above, you can also make use of the provided resolver, an instance of LoaderResolver, to load secondary routing resources.

Of course you still need to implement supports() and load(). Whenever you want to load another resource - for instance a YAML routing configuration file - you can call the import() method:

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// src/AppBundle/Routing/AdvancedLoader.php
namespace AppBundle\Routing;

use Symfony\Component\Config\Loader\Loader;
use Symfony\Component\Routing\RouteCollection;

class AdvancedLoader extends Loader
{
    public function load($resource, $type = null)
    {
        $routes = new RouteCollection();

        $resource = '@AppBundle/Resources/config/import_routing.yml';
        $type = 'yaml';

        $importedRoutes = $this->import($resource, $type);

        $routes->addCollection($importedRoutes);

        return $routes;
    }

    public function supports($resource, $type = null)
    {
        return 'advanced_extra' === $type;
    }
}