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Symfony RESTful API: Basics++ (Course 3)

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Conditionally Serializing Fields with Groups

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Once upon a time, I worked with a client that had a really interesting API requirement. In fact, one that totally violate REST... but it's kinda cool. They said:

When we have one object that relates to another object - like how our programmer relates to a user - sometimes we want to embed the user in the response and sometimes we don't. In fact, we want the API client to tell us via - a query parameter - whether or not they want embedded objects in the response.

Sounds cool...but it totally violates REST because you now have two different URLs that return the same resource... each just returns a different representation. Rules are great - but come on... if this is useful to you, make it happen.

Testing the Deep Functionality

Let's start with a quick test: copy part of testGETProgramer() and name the new method testGETProgrammerDeep(). Now, add a query parameter called ?deep:

247 lines src/AppBundle/Tests/Controller/Api/ProgrammerControllerTest.php
... lines 1 - 5
class ProgrammerControllerTest extends ApiTestCase
{
... lines 8 - 58
public function testGETProgrammerDeep()
{
$this->createProgrammer(array(
'nickname' => 'UnitTester',
'avatarNumber' => 3,
));
$response = $this->client->get('/api/programmers/UnitTester?deep=1');
$this->assertEquals(200, $response->getStatusCode());
... lines 68 - 70
}
... lines 72 - 245
}

The idea is simple: if the client adds ?deep=1, then the API should expose more embedded objects. Use the asserter to say assertResponsePropertyExists(), pass that the $response and the property we'll expect, which is user. Since this will be an entire user object, check specifically for user.username:

247 lines src/AppBundle/Tests/Controller/Api/ProgrammerControllerTest.php
... lines 1 - 5
class ProgrammerControllerTest extends ApiTestCase
{
... lines 8 - 58
public function testGETProgrammerDeep()
{
... lines 61 - 67
$this->asserter()->assertResponsePropertiesExist($response, array(
'user.username'
));
}
... lines 72 - 245
}

Very nice!

Serialization Groups

If you look at this response in the browser, we definitely do not have a user field. But there are only two little things we need to do to add it.

First, expose the user property with @Serializer\Expose():

198 lines src/AppBundle/Entity/Programmer.php
... lines 1 - 21
class Programmer
{
... lines 24 - 65
/**
... lines 67 - 69
* @Serializer\Expose()
*/
private $user;
... lines 73 - 196
}

Of course, it can't be that simple: now the user property would always be included. To avoid that, add @Serializer\Groups() and use a new group called deep:

198 lines src/AppBundle/Entity/Programmer.php
... lines 1 - 21
class Programmer
{
... lines 24 - 65
/**
... lines 67 - 68
* @Serializer\Groups({"deep"})
* @Serializer\Expose()
*/
private $user;
... lines 73 - 196
}

Here's the idea: when you serialize, each property belongs to one or more "groups". If you don't include the @Serializer\Groups annotation above a property, then it will live in a group called Default - with a capital D. Normally, the serializer serializes all properties, regardless of their group. But you can also tell it to serialize only the properties in a different group, or even in a set of groups. We can use groups to serialize the user property under only certain conditions.

But before we get there - I just noticed that the password field is being exposed on my User. That's definitely lame. Fix it by adding the Expose use statement, removing that last part and writing as Serializer instead. That's a nice trick to get that use statement:

86 lines src/AppBundle/Entity/User.php
... lines 1 - 7
use JMS\Serializer\Annotation as Serializer;
... lines 9 - 14
class User implements UserInterface
{
... lines 17 - 84
}

Now set @Serializer\ExclusionPolicy() above the class with all and add @Expose above username:

86 lines src/AppBundle/Entity/User.php
... lines 1 - 9
/**
* @Serializer\ExclusionPolicy("all")
* @ORM\Table(name="battle_user")
* @ORM\Entity(repositoryClass="AppBundle\Repository\UserRepository")
*/
class User implements UserInterface
{
... lines 17 - 23
/**
* @Serializer\Expose()
* @ORM\Column(type="string", unique=true)
*/
private $username;
... lines 29 - 84
}

Back in Programmer.php, remove the "groups" code temporarily and refresh. OK good, only the username is showing. Put that "groups" code back.

Setting the SerializationGroup

Ok... so now, how can we serialize a specific set of groups? To answer that, open ProgrammerController and find showAction(). Follow createApiResponse() into the BaseController and find serialize():

133 lines src/AppBundle/Controller/BaseController.php
... lines 1 - 16
abstract class BaseController extends Controller
{
... lines 19 - 123
protected function serialize($data, $format = 'json')
{
$context = new SerializationContext();
$context->setSerializeNull(true);
return $this->container->get('jms_serializer')
->serialize($data, $format, $context);
}
}

When we serialize, we create this SerializationContext, which holds a few options for serialization. Honestly, there's not much you can control with this, but you can set which groups you want to serialize.

First, get the $request object by fetching the request_stack service and adding getCurrentRequest(). Next, create a new $groups variable and set it to only Default: we always want to serialize the properties in this group:

140 lines src/AppBundle/Controller/BaseController.php
... lines 1 - 16
abstract class BaseController extends Controller
{
... lines 19 - 123
protected function serialize($data, $format = 'json')
{
$context = new SerializationContext();
$context->setSerializeNull(true);
$request = $this->get('request_stack')->getCurrentRequest();
$groups = array('Default');
... lines 131 - 137
}
}

Now say if ($request->query->get('deep')) is true then add deep to $groups. Finish this up with $context->setGroups($groups):

140 lines src/AppBundle/Controller/BaseController.php
... lines 1 - 16
abstract class BaseController extends Controller
{
... lines 19 - 123
protected function serialize($data, $format = 'json')
{
... lines 126 - 129
$groups = array('Default');
if ($request->query->get('deep')) {
$groups[] = 'deep';
}
$context->setGroups($groups);
... lines 135 - 137
}
}

Go Deeper!

You could also use $request->query->getBoolean('deep') instead of get() to convert the deep query parameter into a boolean. See accessing request data for other useful methods.

And just like that, we're able to conditionally show fields. Sweet!

Re-run our test for testGETProgrammerDeep():

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

It passes! To really prove it, refresh the browser. Nope, no user property. Now add ?deep=1 to the URL. That's a cool way to leverage groups.

Wow, nice work guys! We've just taken another huge chunk out of our API with pagination, filtering and a whole lot of cool serialization magic. Ok, now keep going with the next episode!

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.
Symfony 3

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
    }
}
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