Hateoas

Powerful PHP library to support implementing representations for HATEOAS REST web services. Start building truly REST APIs now!

Hateoas

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Installation

The recommended way to install Hateoas is through Composer. Require the willdurand/hateoas package into your composer.json file:

{
    "require": {
        "willdurand/hateoas": "@stable"
    }
}

Protip: you should browse the willdurand/hateoas page to choose a stable version to use, avoid the @stable meta constraint.

Otherwise, install the library and setup the autoloader yourself.

Working With Symfony2

There is a bundle for that! Install the BazingaHateoasBundle, and enjoy!

Usage

Important: For those who use the 1.0 version, you can jump to this documentation page as the following documentation has been written for Hateoas 2.0 and above.

Introduction

Hateoas leverages the Serializer library to provide a nice way to build HATEOAS REST web services. HATEOAS stands for Hypermedia as the Engine of Application State, and adds hypermedia links to your representations (i.e. your API responses). HATEOAS is about the discoverability of actions on a resource.

For instance, let's say you have a User API which returns a representation of a single user as follow:

{
    "user": {
        "id": 123,
        "first_name": "John",
        "last_name": "Doe"
    }
}

In order to tell your API consumers how to retrieve the data for this specific user, you have to add your very first link to this representation, let's call it self as it is the URI for this particular user:

{
    "user": {
        "id": 123,
        "first_name": "John",
        "last_name": "Doe",
        "_links": {
            "self": { "href": "http://example.com/api/users/123" }
        }
    }
}

Let's dig into Hateoas now.

Configuring Links

In Hateoas terminology, links are seen as relations added to resources. It is worth mentioning that relations also refer to embedded resources too, but this topic will be covered in the Embedding Resources section.

A link is a relation which is identified by a name (e.g. self) and that has an href parameter:

use JMS\Serializer\Annotation as Serializer;
use Hateoas\Configuration\Annotation as Hateoas;

/**
 * @Serializer\XmlRoot("user")
 *
 * @Hateoas\Relation("self", href = "expr('/api/users/' ~ object.getId())")
 */
class User
{
    /** @Serializer\XmlAttribute */
    private $id;
    private $firstName;
    private $lastName;

    public function getId() {}
}

In the example above, we configure a self relation that is a link because of the href parameter. Its value, which may look weird at first glance, will be extensively covered in The Expression Language section. This special value is used to generate a URI.

In this section, annotations are used to configure Hateoas. XML and YAML formats are also supported. If you wish, you can use plain PHP too.

Important: you must configure both the Serializer and Hateoas the same way. E.g. if you use YAML for configuring Serializer, use YAML for configuring Hateoas.

The easiest way to try HATEOAS is with the HateoasBuilder. The builder has numerous methods to configure the Hateoas serializer, but we won't dig into them right now (see The HateoasBuilder). Everything works fine out of the box:

use Hateoas\HateoasBuilder;

$hateoas = HateoasBuilder::create()->build();

$user = new User(42, 'Adrien', 'Brault');
$json = $hateoas->serialize($user, 'json');
$xml  = $hateoas->serialize($user, 'xml');

The $hateoas object is an instance of JMS\Serializer\SerializerInterface, coming from the Serializer library. Hateoas does not come with its own serializer, it hooks into the JMS Serializer.

By default, Hateoas uses the Hypertext Application Language (HAL) for JSON serialization. This specifies the structure of the response (e.g. that "links" should live under a _links key):

{
    "id": 42,
    "first_name": "Adrien",
    "last_name": "Brault",
    "_links": {
        "self": {
            "href": "/api/users/42"
        }
    }
}

For XML, Atom Links are used by default:

<user id="42">
    <first_name><![CDATA[Adrien]]></first_name>
    <last_name><![CDATA[Brault]]></last_name>
    <link rel="self" href="/api/users/42"/>
</user>

It is worth mentioning that these formats are the default ones, not the only available ones. You can use different formats through different serializers, and even add your owns.

Now that you know how to add links, let's see how to add embedded resources.

Embedding Resources

Sometimes, it's more efficient to embed related resources rather than link to them, as it prevents clients from having to make extra requests to fetch those resources.

An embedded resource is a named relation that contains data, represented by the embedded parameter.

use JMS\Serializer\Annotation as Serializer;
use Hateoas\Configuration\Annotation as Hateoas;

/**
 * ...
 *
 * @Hateoas\Relation(
 *     "manager",
 *     href = "expr('/api/users/' ~ object.getManager().getId())",
 *     embedded = "expr(object.getManager())",
 *     exclusion = @Hateoas\Exclusion(excludeIf = "expr(object.getManager() === null)")
 * )
 */
class User
{
    ...

    /** @Serializer\Exclude */
    private $manager;
}

Note: You will need to exclude the manager property from the serialization, otherwise both the serializer and Hateoas will serialize it. You will also have to exclude the manager relation when the manager is null, because otherwise an error will occur when creating the href link (calling getId() on null).

Tip: If the manager property is an object that already has a _self link, you can re-use that value for the href instead of repeating it here. See LinkHelper.

$hateoas = HateoasBuilder::create()->build();

$user = new User(42, 'Adrien', 'Brault', new User(23, 'Will', 'Durand'));
$json = $hateoas->serialize($user, 'json');
$xml  = $hateoas->serialize($user, 'xml');

For json, the HAL representation places these embedded relations inside an _embedded key:

{
    "id": 42,
    "first_name": "Adrien",
    "last_name": "Brault",
    "_links": {
        "self": {
            "href": "/api/users/42"
        },
        "manager": {
            "href": "/api/users/23"
        },
    },
    "_embedded": {
        "manager": {
            "id": 23,
            "first_name": "Will",
            "last_name": "Durand",
            "_links": {
                "self": {
                    "href": "/api/users/23"
                }
            }
        }
    }
}

In XML, serializing embedded relations will create new elements:

<user id="42">
    <first_name><![CDATA[Adrien]]></first_name>
    <last_name><![CDATA[Brault]]></last_name>
    <link rel="self" href="/api/users/42"/>
    <link rel="manager" href="/api/users/23"/>
    <manager rel="manager" id="23">
        <first_name><![CDATA[Will]]></first_name>
        <last_name><![CDATA[Durand]]></last_name>
        <link rel="self" href="/api/users/23"/>
    </manager>
</user>

The tag name of an embedded resource is inferred from the @XmlRoot annotation (xml_root_name in YAML, xml-root-name in XML) coming from the Serializer configuration.

Dealing With Collections

The library provides several classes in the Hateoas\Representation\* namespace to help you with common tasks. These are simple classes configured with the library's annotations.

The PaginatedRepresentation and CollectionRepresentation classes are probably the most interesting ones. These are helpful when your resource is actually a collection of resources (e.g. /users is a collection of users). These help you represent the collection and add pagination and limits:

use Hateoas\Representation\PaginatedRepresentation;
use Hateoas\Representation\CollectionRepresentation;

$paginatedCollection = new PaginatedRepresentation(
    new CollectionRepresentation(
        array($user1, $user2, ...),
        'users', // embedded rel
        'users' // xml element name
    ),
    'user_list', // route
    array(), // route parameters
    1, // page
    20, // limit
    4, // total pages
    'page',  // page route parameter name, optional, defaults to 'page'
    'limit', // limit route parameter name, optional, defaults to 'limit'
    false    // generate relative URIs
);

$json = $hateoas->serialize($paginatedCollection, 'json');
$xml  = $hateoas->serialize($paginatedCollection, 'xml');

The CollectionRepresentation class allows you to dynamically configure the collection resources rel, and the xml root element name.

The PaginatedRepresentation is designed to add self, first, and when possible last, next, and previous links.

The RouteAwareRepresentation adds a self relation based on a given route.

You can generate absolute URIs by setting the absolute parameter to true in both the PaginatedRepresentation and the RouteAwareRepresentation.

The Hateoas library also provides a PagerfantaFactory to easily build PaginatedRepresentation from a Pagerfanta instance. If you use the Pagerfanta library, this is an easier way to create the collection representations:

use Hateoas\Configuration\Route;
use Hateoas\Representation\Factory\PagerfantaFactory;

$pagerfantaFactory   = new PagerfantaFactory(); // you can pass the page,
                                                // and limit parameters name
$paginatedCollection = $pagerfantaFactory->createRepresentation(
    $pager,
    new Route('user_list', array())
);

$json = $hateoas->serialize($paginatedCollection, 'json');
$xml  = $hateoas->serialize($paginatedCollection, 'xml');

You would get the following JSON content:

{
    "page": 1,
    "limit": 10,
    "pages": 1,
    "_links": {
        "self": {
            "href": "/api/users?page=1&limit=10"
        },
        "first": {
            "href": "/api/users?page=1&limit=10"
        },
        "last": {
            "href": "/api/users?page=1&limit=10"
        }
    },
    "_embedded": {
        "items": [
            { "id": 123 },
            { "id": 456 }
        ]
    }
}

And the following XML content:

<?xml version="1.0" encoding="UTF-8"?>
<collection page="1" limit="10" pages="1">
    <user id="123"></user>
    <user id="456"></user>
    <link rel="self" href="/api/users?page=1&amp;limit=10" />
    <link rel="first" href="/api/users?page=1&amp;limit=10" />
    <link rel="last" href="/api/users?page=1&amp;limit=10" />
</collection>

If you want to customize the inlined CollectionRepresentation, pass one as third argument of the createRepresentation() method:

use Hateoas\Representation\Factory\PagerfantaFactory;

$pagerfantaFactory   = new PagerfantaFactory(); // you can pass the page and limit parameters name
$paginatedCollection = $pagerfantaFactory->createRepresentation(
    $pager,
    new Route('user_list', array()),
    new CollectionRepresentation(
        $pager->getCurrentPageResults(),
        'users',
        'users',
        new Exclusion(...)
    )
);

$json = $hateoas->serialize($paginatedCollection, 'json');
$xml  = $hateoas->serialize($paginatedCollection, 'xml');

Representations

As mentionned in the previous section, representations are classes configured with the library's annotations in order to help you with common tasks. The collection representations are described in Dealing With Collection.

VndErrorRepresentation

The VndErrorRepresentation allows you to describe an error response following the vnd.error specification.

$error = new VndErrorRepresentation(
    'Validation failed',
    42,
    new Relation('help', 'http://.../', null, array('title' => 'Error Information')),
    new Relation('describes', 'http://.../', null, array('title' => 'Error Description'))
);

Serializing such a representation in XML and JSON would give you the following outputs:

<?xml version="1.0" encoding="UTF-8"?>
    <resource logref="42">
    <message><![CDATA[Validation failed]]></message>
    <link rel="help" href="http://.../" title="Error Information"/>
    <link rel="describes" href="http://.../" title="Error Description"/>
</resource>
{
    "message": "Validation failed",
    "logref": 42,
    "_links": {
        "help": {
            "href": "http://.../",
            "title": "Error Information"
        },
        "describes": {
            "href": "http://.../",
            "title": "Error Description"
        }
    }
}

Hint: it is recommended to create your own error classes that extend the VndErrorRepresentation class.

The Expression Language

Hateoas relies on the powerful Symfony ExpressionLanguage component to retrieve values such as links, ids or objects to embed.

Each time you fill in a value (e.g. a Relation href in annotations or YAML), you can either pass a hardcoded value or an expression. In order to use the Expression Language, you have to use the expr() notation:

/**
 * @Hateoas\Relation("self", href = "expr('/api/users/' ~ object.getId())")
 */

You can learn more about the Expression Syntax by reading the official documentation: The Expression Syntax.

Context

Natively, a special variable named object is available in each expression, and represents the current object:

expr(object.getId())

We call such a variable a context variable.

You can add your own context variables to the Expression Language context by adding them to the ExpressionEvaluator.

Adding Your Own Context Variables

Using the HateoasBuilder, call the setExpressionContextVariable() method to add new context variables:

use Hateoas\HateoasBuilder;

$hateoas = HateoasBuilder::create()
    ->setExpressionContextVariable('foo', new Foo())
    ->build();

The foo variable is now available:

expr(foo !== null)
Expression Functions

Expression Functions are custom functions used to extend the Expression Language as explained in the Extending the ExpressionLanguage, part of the Symfony documentation.

Hateoas provides core expression functions such as the LinkExpressionFunction described in LinkHelper - The link Function, but you can also write your own function. The ExpressionFunctionInterface is designed to represent an expression function. Adding a new expression function is a matter of implementing this interface and registering by calling the registerExpressionFunction() method on the HateoasBuilder.

URL Generators

Since you can use the Expression Language to define the relations links (href key), you can do a lot by default. However if you are using a framework, chances are that you will want to use routes to build links.

You will first need to configure an UrlGenerator on the builder. You can either implement the Hateoas\UrlGenerator\UrlGeneratorInterface, or use the Hateoas\UrlGenerator\CallableUrlGenerator:

use Hateoas\UrlGenerator\CallableUrlGenerator;

$hateoas = HateoasBuilder::create()
    ->setUrlGenerator(
        null, // By default all links uses the generator configured with the null name
        new CallableUrlGenerator(function ($route, array $parameters, $absolute) use ($myFramework) {
            return $myFramework->generateTheUrl($route, $parameters, $absolute);
        })
    )
    ->build()
;

You will then be able to use the @Route annotation:

use Hateoas\Configuration\Annotation as Hateoas;

/**
 * @Hateoas\Relation(
 *      "self",
 *      href = @Hateoas\Route(
 *          "user_get",
 *          parameters = {
 *              "id" = "expr(object.getId())"
 *          }
 *      )
 * )
 */
class User
{
    "id": 42,
    "first_name": "Adrien",
    "last_name": "Brault",
    "_links": {
        "self": {
            "href": "/api/users/42"
        }
    }
}

Note that the library comes with a SymfonyUrlGenerator. For example, to use it in Silex:

use Hateoas\UrlGenerator\SymfonyUrlGenerator;

$hateoas = HateoasBuilder::create()
    ->setUrlGenerator(null, new SymfonyUrlGenerator($app['url_generator']))
    ->build()
;

Helpers

Hateoas provides a set of helpers to ease the process of building APIs.

LinkHelper

The LinkHelper class provides a getLinkHref($object, $rel, $absolute = false) method that allows you to get the href value of any object, for any given relation name. It is able to generate a URI (either absolute or relative) from any link relation:

$user = new User(123, 'William', 'Durand');

$linkHelper->getLinkHref($user, 'self');
// /api/users/123

$linkHelper->getLinkHref($user, 'self', true);
// http://example.com/api/users/123
The link Function

The feature above is also available in your expressions (cf. The Expression Language) through the link(object, rel, absolute) function:

/**
 * @Hateoas\Relation(
 *     "self",
 *     href = @Hateoas\Route("post_get", parameters = {"id" = "expr(object.getId())"})
 * )
 */
class Post {}

/**
 * @Hateoas\Relation(
 *     "self",
 *     href = @Hateoas\Route("user_get", parameters = {"id" = "expr(object.getId())"})
 * )
 * @Hateoas\Relation(
 *     "post",
 *     href = "expr(link(object.getPost(), 'self', true))"
 * )
 * @Hateoas\Relation(
 *     "relative",
 *     href = "expr(link(object.getRelativePost(), 'self'))"
 * )
 */
class User
{
    ...

    public function getPost()
    {
        return new Post(456);
    }

    public function getRelativePost()
    {
        return new Post(789);
    }
}

Pay attention to the href expressions for the post and relative relations, as well as their corresponding values in the following JSON content:

{
    "user": {
        "id": 123,
        "first_name": "William",
        "last_name": "Durand",
        "_links": {
            "self": { "href": "http://example.com/api/users/123" },
            "post": { "href": "http://example.com/api/posts/456" },
            "relative": { "href": "/api/posts/789" }
        }
    }
}

It is worth mentioning that you can force whether you want an absolute or relative URI by using the third argument in both the getLinkHref() method and the link function.

Important: by default, all URIs will be relative, even those which are defined as absolute in their configuration.

$linkHelper->getLinkHref($user, 'post');
// /api/posts/456

$linkHelper->getLinkHref($user, 'post', true);
// http://example.com/api/posts/456

$linkHelper->getLinkHref($user, 'relative');
// /api/posts/789

$linkHelper->getLinkHref($user, 'relative', true);
// http://example.com/api/posts/789

Twig Extensions

Hateoas also provides a set of Twig extensions.

LinkExtension

The LinkExtension allows you to use the LinkHelper into your Twig templates, so that you can generate links in your HTML templates for instance.

This extension exposes the getLinkHref() helper's method through the link_href Twig function:

{{ link_href(user, 'self') }}
{# will generate: /users/123 #}

{{ link_href(will, 'self', false) }}
{# will generate: /users/123 #}

{{ link_href(will, 'self', true) }}
{# will generate: http://example.com/users/123 #}

Serializers & Formats

Hateoas provides a set of serializers. Each serializer allows you to generate either XML or JSON content following a specific format, such as HAL, or Atom Links for instance.

The JsonHalSerializer

The JsonHalSerializer allows you to generate HAL compliant relations in JSON. It is the default JSON serializer in Hateoas.

HAL provides its linking capability with a convention which says that a resource object has a reserved property called _links. This property is an object that contains links. These links are key'ed by their link relation.

HAL also describes another convention which says that a resource may have another reserved property named _embedded. This property is similar to _links in that embedded resources are key'ed by relation name. The main difference is that rather than being links, the values are resource objects.

{
    "message": "Hello, World!",
    "_links": {
        "self": {
            "href": "/notes/0"
        }
    },
    "_embedded": {
        "associated_events": [
            {
                "name": "SymfonyCon",
                "date": "2013-12-12T00:00:00+0100"
            }
        ]
    }
}

 The XmlSerializer

The XmlSerializer allows you to generate Atom Links into your XML documents. It is the default XML serializer.

<?xml version="1.0" encoding="UTF-8"?>
<note>
    <message><![CDATA[Hello, World!]]></message>
    <link rel="self" href="/notes/0" />
    <events rel="associated_events">
        <event>
            <name><![CDATA[SymfonyCon]]></name>
            <date><![CDATA[2013-12-12T00:00:00+0100]]></date>
        </event>
    </events>
</note>

The XmlHalSerializer

The XmlHalSerializer allows you to generate HAL compliant relations in XML.

HAL in XML is similar to HAL in JSON in the sense that it describes link tags and resource tags.

Note: the self relation will actually become an attribute of the main resource instead of being a link tag. Other links will be generated as link tags.

<?xml version="1.0" encoding="UTF-8"?>
<note href="/notes/0">
    <message><![CDATA[Hello, World!]]></message>

    <resource rel="associated_events">
        <name><![CDATA[SymfonyCon]]></name>
        <date><![CDATA[2013-12-12T00:00:00+0100]]></date>
    </resource>
</note>

Adding New Serializers

For JSON related formats, you must implement the JsonSerializerInterface interface, and for XML related formats, you must implement the XmlSerializerInterface. Both interfaces describe two methods to serialize links and embedded relations.

The HateoasBuilder

The HateoasBuilder class is used to easily configure Hateoas thanks to a powerful and fluent API.

use Hateoas\HateoasBuilder;

$hateoas = HateoasBuilder::create()
    ->setCacheDir('/path/to/cache/dir')
    ->setDebug($trueOrFalse)
    ->setDefaultXmlSerializer()
    ...
    ->build();

All the methods below return the current builder, so that you can chain them.

XML Serializer

JSON Serializer

URL Generator

Expression Evaluator/Expression Language

Relation Provider

(JMS) Serializer Specific

Please read the official Serializer documentation for more details.

Others

Configuring a Cache Directory

Both the serializer and the Hateoas libraries collect metadata about your objects from various sources such as YML, XML, or annotations. In order to make this process as efficient as possible, it is recommended that you allow the Hateoas library to cache this information. To do that, configure a cache directory:

$builder = \Hateoas\HateoasBuilder::create();

$hateoas = $builder
    ->setCacheDir($someWritableDir)
    ->build();

Configuring Metadata Locations

Hateoas supports several metadata sources. By default, it uses Doctrine annotations, but you may also store metadata in XML, or YAML files. For the latter, it is necessary to configure a metadata directory where those files are located:

$hateoas = \Hateoas\HateoasBuilder::create()
    ->addMetadataDir($someDir)
    ->build();

Hateoas would expect the metadata files to be named like the fully qualified class names where all \ are replaced with .. If you class would be named Vendor\Package\Foo the metadata file would need to be located at $someDir/Vendor.Package.Foo.(xml|yml).

Extending The Library

Hateoas allows frameworks to dynamically add relations to classes by providing an extension point at configuration level. This feature can be useful for those who want to to create a new layer on top of Hateoas, or to add "global" relations rather than copying the same configuration on each class.

In order to leverage this mechanism, the ConfigurationExtensionInterface interface has to be implemented:

use Hateoas\Configuration\Metadata\ConfigurationExtensionInterface;
use Hateoas\Configuration\Metadata\ClassMetadataInterface;
use Hateoas\Configuration\Relation;

class AcmeFooConfigurationExtension implements ConfigurationExtensionInterface
{
    /**
     * {@inheritDoc}
     */
    public function decorate(ClassMetadataInterface $classMetadata)
    {
        if (0 === strpos('Acme\Foo\Model', $classMetadata->getName())) {
            // Add a "root" relation to all classes in the `Acme\Foo\Model` namespace
            $classMetadata->addRelation(
                new Relation(
                    'root',
                    '/'
                )
            );
        }
    }
}

You can access the existing relations loaded from Annotations, XML, or YAML with $classMetadata->getRelations().

If the $classMetadata has relations, or if you add relations to it, its relations will be cached. So if you read configuration files (Annotations, XML, or YAML), make sure to reference them on the class metadata:

$classMetadata->fileResources[] = $file;

Reference

XML

<?xml version="1.0" encoding="UTF-8"?>
<serializer>
<class name="Acme\Demo\Representation\User" h:providers="Class::getRelations, getRelations" xmlns:h="https://github.com/willdurand/Hateoas">
        <h:relation rel="self">
            <h:href uri="http://acme.com/foo/1" />
        </h:relation>
        <h:relation rel="expr(object.getFriendsDynamicRel())">
            <h:href router="user_friends" generator="my_custom_generator">
                <h:parameter name="id" value="expr(object.getId())" />
                <h:parameter name="page" value="1" />
            </h:ref>
            <h:embedded xml-element-name="users">
                <h:content>expr(object.getFriends())</h:content>
                <h:exclusion ... />
            </h:embedded>
            <h:exclusion groups="Default, user_full" since-version="1.0" until-version="2.2" exclude-if="expr(object.getFriends() === null)" />
        </h:relation>
    </class>
</serializer>

See the hateoas.xsd file for more details.

YAML

Acme\Demo\Representation\User:
    relations:
        -   rel: self
            href: http://acme.com/foo/1
        -   rel: expr(object.getFriendsDynamicRel())
            href:
                route: user_friends
                parameters:
                    id: expr(object.getId())
                    page: 1
                generator: my_custom_generator
            embedded:
                content: expr(object.getFriends())
                xmlElementName: users
                exclusion: ...
            exclusion:
                groups: [Default, user_full]
                since_version: 1.0
                until_version: 2.2
                exclude_if: expr(object.getFriends() === null)

    relation_providers: [ 'Class::getRelations', 'getRelations' ]

Annotations

@Relation

This annotation can be defined on a class.

use Hateoas\Configuration\Annotation as Hateoas;

/**
 * @Hateoas\Relation(
 *     name = "self",
 *     href = "http://hello",
 *     embedded = "expr(object.getHello())",
 *     attributes = { "foo" = "bar" },
 *     exclusion = ...,
 * )
 */
Property Required Content Expression language
name Yes string Yes
href If embedded is not set string / @Route Yes
embedded If href is not set string / @Embedded Yes
attributes No array Yes on key and values
exclusion No @Exclusion N/A

Important: attributes are only used on link relations (i.e. combined with the href property, not with the embedded one).

@Route

use Hateoas\Configuration\Annotation as Hateoas;

/**
 * @Hateoas\Relation(
 *     name = "self",
 *     href = @Hateoas\Route(
 *         "user_get",
 *         parameters = { "id" = "expr(object.getId())" },
 *         absolute = true,
 *         generator = "my_custom_generator"
 *     )
 * )
 */

This annotation can be defined in the href property of the @Relation annotation. This is allows you to your URL generator, if you have configured one.

Property Required Content Expression language
name Yes string Yes
parameters Defaults to array() array / string Yes (string + array key/values)
absolute Defaults to false boolean / string Yes
generator No string / null No

@Embedded

use Hateoas\Configuration\Annotation as Hateoas;

/**
 * @Hateoas\Relation(
 *     name = "friends",
 *     embedded = @Hateoas\Embedded(
 *         "expr(object.getFriends())",
 *         exclusion = ...,
 *         xmlElementName = "users"
 *     )
 * )
 */

This annotation can be defined in the embedded property of the @Relation annotation. It is useful if you need configure the exclusion or xmlElementName options for the embedded resource.

Property Required Content Expression language
content Yes string / array Yes (string)
exclusion Defaults to array() @Exclusion N/A
xmlElementName Defaults to array() string Yes

@Exclusion

This annotation can be defined in the exclusion property of both the @Relation and @Embedded annotations.

Property Required Content Expression language
groups No array No
sinceVersion No float / integer No
untilVersion No float / integer No
maxDepth No integer No
excludeIf No string / boolean Yes

All values except excludeIf act the same way as when they are used directly on the regular properties with the serializer.

excludeIf expects a boolean and is helpful when another expression would fail under some circumstances. In this example, if the getManager method is null, you should exclude it to prevent the URL generation from failing:

/**
 * @Hateoas\Relation(
 *     "manager",
 *     href = @Hateoas\Route(
 *         "user_get",
 *         parameters = { "id" = "expr(object.getManager().getId())" }
 *     ),
 *     exclusion = @Hateoas\Exclusion(excludeIf = "expr(null === object.getManager())")
 * )
 */
class User
{
    public function getId() {}

    /**
     * @return User|null
     */
    public function getManager() {}
}

@RelationProvider

This annotation can be defined on a class.

Property Required Content Expression language
name Yes string No

The can be:

use Hateoas\Configuration\Metadata\ClassMetadataInterface;
use Hateoas\Configuration as Hateoas;

class MyRelationProvider
{
    public function addRelations($object, ClassMetadataInterface $classMetadata)
    {
        // You need to return the relations
        // Adding the relations to the $classMetadata won't work
        return array(
            new Hateoas\Relation(
                'self',
                new Hateoas\Route(
                    'foo_get',
                    array('id' => 'expr(object.getId())')
                )
            )
        );
    }
}