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Super Custom Serialization Fields

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The Serialization Visitor

Back in the subscriber, create a new variable called $visitor and set it to $event->getVisitor(). The visitor is kind of in charge of the serialization process. And since we know we're serializing to JSON, this will be an instance of JsonSerializationVisitor. Write an inline doc for that and add a use statement up top. That will give us autocompletion:

... lines 1 - 6
use JMS\Serializer\JsonSerializationVisitor;
class LinkSerializationSubscriber implements EventSubscriberInterface
{
public function onPostSerialize(ObjectEvent $event)
{
/** @var JsonSerializationVisitor $visitor */
$visitor = $event->getVisitor();
... line 15
}
... lines 17 - 28
}

Oh, hey, look at this - that class has a method on it called addData(). We can use it to add whatever cool custom fields we want. Add that new uri field, but just set it to the classic FOO value for now:

... lines 1 - 12
/** @var JsonSerializationVisitor $visitor */
$visitor = $event->getVisitor();
$visitor->addData('uri', 'FOO');
... lines 16 - 30

Registering the Subscriber

The last thing we need to do - which you can probably guess - is register this as a service. In services.yml, add the service - how about link_serialization_subscriber. Add the class and skip arguments - we don't have any yet. But we do need a tag so that the JMS Serializer knows about our class. Set the tag name to jms_serializer.event_subscriber:

... lines 1 - 5
services:
... lines 7 - 29
link_serialization_subscriber:
class: AppBundle\Serializer\LinkSerializationSubscriber
tags:
- { name: jms_serializer.event_subscriber }

Ok, try the test! Copy the method name, head to the terminal and run:

./bin/phpunit -c app --filter testGETProgrammer

and then paste in the name. This method name matches a few tests, so we'll see more than just our one test run. Yes, it fails... but in a good way!

FOO does not match /api/programmers/UnitTester.

Above, we do have the new, custom uri field.

Making the URI Dynamic

This means we're almost done. To generate the real URI, we need the router. Add the __construct() method with a RouterInterface argument. I'll use the option+enter shortcut to create that property and set it:

... lines 1 - 7
use Symfony\Component\Routing\RouterInterface;
... lines 9 - 10
class LinkSerializationSubscriber implements EventSubscriberInterface
{
private $router;
public function __construct(RouterInterface $router)
{
$this->router = $router;
}
... lines 19 - 45
}

In onPostSerialize() say $programmer = $event->getObject();. Because of our configuration below, we know this will only be called when the object is a Programmer. Add some inline documentation for the programmer and plug in its use statement:

... lines 1 - 8
use AppBundle\Entity\Programmer;
class LinkSerializationSubscriber implements EventSubscriberInterface
{
... lines 13 - 19
public function onPostSerialize(ObjectEvent $event)
{
/** @var JsonSerializationVisitor $visitor */
$visitor = $event->getVisitor();
/** @var Programmer $programmer */
$programmer = $event->getObject();
... lines 26 - 32
}
... lines 34 - 45
}

Finally, for the data type $this->router->generate() and pass it api_programmers_show and an array containing nickname set to $programmer->getNickname():

... lines 1 - 10
class LinkSerializationSubscriber implements EventSubscriberInterface
{
... lines 13 - 19
public function onPostSerialize(ObjectEvent $event)
{
... lines 22 - 26
$visitor->addData(
'uri',
$this->router->generate('api_programmers_show', [
'nickname' => $programmer->getNickname()
])
);
}
... lines 34 - 45
}

Cool! Now, go back to services.yml and add an arguments key with just @router:

... lines 1 - 5
services:
... lines 7 - 29
link_serialization_subscriber:
class: AppBundle\Serializer\LinkSerializationSubscriber
arguments: ['@router']
tags:
- { name: jms_serializer.event_subscriber }

Ok, moment of truth! Run the test!

./bin/phpunit -c app --filter testGETProgrammer

And... it's failing. Ah, the URL has ?nickname=UnitTester. Woh woh. I bet that's my fault. The name of the route in onPostSerialize() should be api_programmers_show:

... lines 1 - 10
class LinkSerializationSubscriber implements EventSubscriberInterface
{
... lines 13 - 19
public function onPostSerialize(ObjectEvent $event)
{
... lines 22 - 26
$visitor->addData(
'uri',
$this->router->generate('api_programmers_show', [
'nickname' => $programmer->getNickname()
])
);
}
... lines 34 - 45
}

Re-run the test:

./bin/phpunit -c app --filter testGETProgrammer

It's still failing, but for a new reason. This time it doesn't like the app_test.php at the beginning of the link URI. Where's that coming from?

The test class extends an ApiTestCase: we made this in an earlier episode. This app already has a test environment and it configures a test database connection. If we can force every URL through app_test.php, it'll use that test database, and we'll be really happy:

... lines 1 - 20
class ApiTestCase extends KernelTestCase
{
... lines 23 - 46
public static function setUpBeforeClass()
{
... lines 49 - 59
// guaranteeing that /app_test.php is prefixed to all URLs
self::$staticClient->getEmitter()
->on('before', function(BeforeEvent $event) {
$path = $event->getRequest()->getPath();
if (strpos($path, '/api') === 0) {
$event->getRequest()->setPath('/app_test.php'.$path);
}
});
... lines 68 - 69
}
... lines 71 - 295
}

We did a cool thing with Guzzle to accomplish this: automatically prefixing our requests with app_test.php. But because of that, when we generate URLs, they will also have app_test.php. That's a good thing in general, just not when we're comparing URLs in a test.

Copy that path and create a helper function at the bottom of ApiTestCase called protected function adjustUri(). Make this return /app_test.php plus the $uri. This method can help when comparing expected URI's:

... lines 1 - 20
class ApiTestCase extends KernelTestCase
{
... lines 23 - 282
/**
* Call this when you want to compare URLs in a test
*
* (since the returned URL's will have /app_test.php in front)
*
* @param string $uri
* @return string
*/
protected function adjustUri($uri)
{
return '/app_test.php'.$uri;
}
}

Now, in ProgrammerControllerTest, just wrap the expected URI in $this->adjustUri():

... lines 1 - 5
class ProgrammerControllerTest extends ApiTestCase
{
... lines 8 - 35
public function testGETProgrammer()
{
... lines 38 - 51
$this->asserter()->assertResponsePropertyEquals(
$response,
'uri',
$this->adjustUri('/api/programmers/UnitTester')
);
}
... lines 58 - 231
}

This isn't a particularly incredible solution, but now we can properly test things. Run the tests again...

./bin/phpunit -c app --filter testGETProgrammer

And... It's green! Awesome!

Method 2: Adding Custom Fields

One last thing! I mentioned that there are two ways to add super-custom fields like uri. Using a serializer subscriber is the first. But sometimes, your API representation will look much different than your entity. Imagine we had some crazy endpoint that returned info about a Programmer mixed with details about their last 3 battles, the last time they fought and the current weather in their hometown.

Can you imagine trying to do this? You'll need multiple @VirtualProperty methods and probably some craziness inside an event subscriber. It might work, but it'll look ugly and be confusing.

In this case, there's a much better way: create a new class with the exact properties you need. Then, instantiate it, populate the object in your controller and serialize it. This class isn't an entity - it's just there to model your API response. I love this approach and recommend it as soon as you're doing more than just a few serialization customizations to a class.

Leave a comment!

This tutorial uses an older version of Symfony. The concepts of REST and serialization are still valid, but I recommend using API Platform in new Symfony apps.

What PHP libraries does this tutorial use?

// composer.json
{
    "require": {
        "php": ">=5.3.3",
        "symfony/symfony": "2.6.*", // v2.6.11
        "doctrine/orm": "~2.2,>=2.2.3,<2.5", // v2.4.7
        "doctrine/dbal": "<2.5", // v2.4.4
        "doctrine/doctrine-bundle": "~1.2", // v1.4.0
        "twig/extensions": "~1.0", // v1.2.0
        "symfony/assetic-bundle": "~2.3", // v2.6.1
        "symfony/swiftmailer-bundle": "~2.3", // v2.3.8
        "symfony/monolog-bundle": "~2.4", // v2.7.1
        "sensio/distribution-bundle": "~3.0,>=3.0.12", // v3.0.21
        "sensio/framework-extra-bundle": "~3.0,>=3.0.2", // v3.0.7
        "incenteev/composer-parameter-handler": "~2.0", // v2.1.0
        "hautelook/alice-bundle": "0.2.*", // 0.2
        "jms/serializer-bundle": "0.13.*", // 0.13.0
        "white-october/pagerfanta-bundle": "^1.0" // v1.2.4
    },
    "require-dev": {
        "sensio/generator-bundle": "~2.3", // v2.5.3
        "behat/behat": "~3.0", // v3.0.15
        "behat/mink-extension": "~2.0.1", // v2.0.1
        "behat/mink-goutte-driver": "~1.1.0", // v1.1.0
        "behat/mink-selenium2-driver": "~1.2.0", // v1.2.0
        "phpunit/phpunit": "~4.6.0" // 4.6.4
    }
}