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How to Create a custom Route Loader

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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.

A custom route loader does not enable your bundle to inject routes without the need to modify the routing configuration (e.g. app/config/routing.yml) manually. If your bundle provides routes, whether via a configuration file, like the WebProfilerBundle does, or via a custom route loader, like the FOSRestBundle does, an entry in the routing configuration is always necessary.

Note

There are many bundles out there that use their own route loaders to accomplish cases like those described above, for instance FOSRestBundle, JMSI18nRoutingBundle, KnpRadBundle and SonataAdminBundle.

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 and @Method 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.

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's better not to implement LoaderInterface yourself, but extend from Loader.

The sample loader below supports loading routing resources with a type of extra. The type extra isn't important - you can just invent any resource type you want. 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 $loaded = false;

    public function load($resource, $type = null)
    {
        if (true === $this->loaded) {
            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->loaded = 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 }
    
  • XML
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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>
    
  • PHP
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    use Symfony\Component\DependencyInjection\Definition;
    
    $container
        ->setDefinition(
            'app.routing_loader',
            new Definition('AppBundle\Routing\ExtraLoader')
        )
        ->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.

Using the custom Loader

If you did nothing else, your custom routing loader would not be called. Instead, you only need to add a few extra lines to the routing configuration:

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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>
    
  • PHP
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    // app/config/routing.php
    use Symfony\Component\Routing\RouteCollection;
    
    $collection = new RouteCollection();
    $collection->addCollection($loader->import('.', 'extra'));
    
    return $collection;
    

The important part here is the type key. Its value should be "extra" as this is the type which the ExtraLoader supports and this will make sure its load() method gets called. The resource key is insignificant for the ExtraLoader, so it is set to ".".

Note

The routes defined using custom route loaders will be automatically cached by the framework. So whenever you change something in the loader class itself, don't forget to clear the cache.

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)
    {
        $collection = new RouteCollection();

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

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

        $collection->addCollection($importedRoutes);

        return $collection;
    }

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

Note

The resource name and type of the imported routing configuration can be anything that would normally be supported by the routing configuration loader (YAML, XML, PHP, annotation, etc.).

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.