ZF HAL

Introduction

This module provides the ability to generate Hypermedia Application Language JSON representations.

Requirements

Please see the composer.json file.

Installation

Run the following composer command:

$ composer require zfcampus/zf-hal

Alternately, manually add the following to your composer.json, in the require section:

"require": {
    "zfcampus/zf-hal": "^1.4"
}

And then run composer update to ensure the module is installed.

Finally, add the module name to your project's config/application.config.php under the modules key:

return [
    /* ... */
    'modules' => [
        /* ... */
        'ZF\Hal',
    ],
    /* ... */
];

zf-component-installer

If you use zf-component-installer, that plugin will install zf-hal as a module for you.

Configuration

User Configuration

This module utilizes the top level key zf-hal for user configuration.

Key: `renderer`

This is a configuration array used to configure the zf-hal Hal view helper/controller plugin. It consists of the following keys:

default_hydrator - when present, this named hydrator service will be used as the default hydrator by the Hal plugin when no hydrator is configured for an entity class.
render_embedded_entities - boolean, default true, to render full embedded entities in HAL responses; if false, embedded entities will contain only their relational links.
render_embedded_collections - boolean, default is true, to render collections in HAL responses; if false, only a collection's relational links will be rendered.
hydrators - a map of entity class names to hydrator service names that the Hal plugin can use when hydrating entities.

Key: `metadata_map`

The metadata map is used to hint to the Hal plugin how it should render objects of specific class types. When the Hal plugin encounters an object found in the metadata map, it will use the configuration for that class when creating a representation; this information typically indicates how to generate relational links, how to serialize the object, and whether or not it represents a collection.

Each class in the metadata map may contain one or more of the following configuration keys:

entity_identifier_name - name of the class property (after serialization) used for the identifier.
route_name - a reference to the route name used to generate self relational links for the collection or entity.
route_identifier_name - the identifier name used in the route that will represent the entity identifier in the URI path. This is often different than the entity_identifier_name as each variable segment in a route must have a unique name.
hydrator - the hydrator service name to use when serializing an entity.
is_collection - boolean; set to true when the class represents a collection.
links - an array of configuration for constructing relational links; see below for the structure of links.
entity_route_name - route name for embedded entities of a collection.
route_params - an array of route parameters to use for link generation.
route_options - an array of options to pass to the router during link generation.
url - specific URL to use with this resource, if not using a route.
max_depth - integer; limit to what nesting level entities and collections are rendered; if the limit is reached, only self links will be rendered. default value is null, which means no limit: if unlimited circular references are detected, an exception will be thrown to avoid infinite loops.
force_self_link - boolean; set whether a self-referencing link should be automatically generated for the entity. Defaults to true (since its recommended).

The links property is an array of arrays, each with the following structure:

[
    'rel'   => 'link relation',
    'url'   => 'string absolute URI to use', // OR
    'route' => [
        'name'    => 'route name for this link',
        'params'  => [ /* any route params to use for link generation */ .,
        'options' => [ /* any options to pass to the router */ .,
    .,
.,
// repeat as needed for any additional relational links

Key: `options`

The options key is used to configure general options of the Hal plugin. For now we have only one option available who contains the following configuration key:

use_proxy - boolean; set to true when you are using a proxy (for using HTTP_X_FORWARDED_PROTO, HTTP_X_FORWARDED_HOST, and HTTP_X_FORWARDED_PORT instead of SSL_HTTPS, HTTP_HOST, SERVER_PORT)

System Configuration

The following configuration is present to ensure the proper functioning of this module in a ZF2-based application.

// Creates a "HalJson" selector for use with zfcampus/zf-content-negotiation
'zf-content-negotiation' => [
    'selectors' => [
        'HalJson' => [
            'ZF\Hal\View\HalJsonModel' => [
                'application/json',
                'application/*+json',
            ],
        ],
    ],
],

ZF2 Events

Events

ZF\Hal\Plugin\Hal Event Manager

The ZF\Hal\Plugin\Hal triggers several events during its lifecycle. From the EventManager instance composed into the HAL plugin, you may attach to the following events:

renderCollection
renderCollection.post
renderEntity
renderEntity.post
createLink
renderCollection.entity
getIdFromEntity

As an example, you could listen to the renderEntity event as follows (the following is done within a Module class for a ZF2 module and/or Apigility API module):

class Module
{
    public function onBootstrap($e)
    {
        $app = $e->getTarget();
        $services = $app->getServiceManager();
        $helpers  = $services->get('ViewHelperManager');
        $hal      = $helpers->get('Hal');

        // The HAL plugin's EventManager instance does not compose a SharedEventManager,
        // so you must attach directly to it.
        $hal->getEventManager()->attach('renderEntity', [$this, 'onRenderEntity']);
    }

    public function onRenderEntity($e)
    {
        $entity = $e->getParam('entity');
        if (! $entity->getEntity() instanceof SomeTypeIHaveDefined) {
            // do nothing
            return;
        }

        // Add a "describedBy" relational link
        $entity->getLinks()->add(\ZF\Hal\Link\Link::factory([
            'rel' => 'describedBy',
            'route' => [
                'name' => 'my/api/docs',
            ],
        ]));
    }
}

Notes on individual events:

renderCollection defines one parameter, collection, which is the ZF\Hal\Collection being rendered.
renderCollection.post defines two parameters: collection, which is the ZF\Hal\Collection being rendered, and payload, an ArrayObject representation of the collection, including the page count, size, and total items, and links.
renderEntity defines one parameter, entity, which is the ZF\Hal\Entity being rendered.
renderEntity.post defines two parameters: entity, which is the ZF\Hal\Entity being rendered, and payload, an ArrayObject representation of the entity, including links.
createLink defines the following event parameters:
- route, the route name to use when generating the link, if any.
- id, the entity identifier value to use when generating the link, if any.
- entity, the entity for which the link is being generated, if any.
- params, any additional routing parameters to use when generating the link.
renderCollection.entity defines the following event parameters:
- collection, the ZF\Hal\Collection to which the entity belongs.
- entity, the current entity being rendered; this may or may not be a ZF\Hal\Entity.
- route, the route name for the current entity.
- routeParams, route parameters to use when generating links for the current entity.
- routeOptions, route options to use when generating links for the current entity.
getIdFromEntity defines one parameter, entity, which is an array or object from which an identifier needs to be extracted.
fromLink.pre (since 1.5.0) defines one parameter, linkDefinition, which is a ZF\Hal\Link\Link instance. This is generally useful from ZF\Rest\RestController::create(), when you may want to manipulate the self relational link for purposes of generating the Link header.

Listeners

ZF\Hal\Module::onRender

This listener is attached to MvcEvent::EVENT_RENDER at priority 100. If the controller service result is a HalJsonModel, this listener attaches the ZF\Hal\JsonStrategy to the view at priority 200.

ZF2 Services

Models

ZF\Hal\Collection

Collection is responsible for modeling general collections as HAL collections, and composing relational links.

ZF\Hal\Entity

Entity is responsible for modeling general purpose entities and plain objects as HAL entities, and composing relational links.

ZF\Hal\Link\Link

Link is responsible for modeling a relational link. The Link class also has a static factory() method that can take an array of information as an argument to produce valid Link instances.

ZF\Hal\Link\LinkCollection

LinkCollection is a model responsible for aggregating a collection of Link instances.

ZF\Hal\Metadata\Metadata

Metadata is responsible for collecting all the necessary dependencies, hydrators and other information necessary to create HAL entities, links, or collections.

ZF\Hal\Metadata\MetadataMap

The MetadataMap aggregates an array of class name keyed Metadata instances to be used in producing HAL entities, links, or collections.

Extractors

ZF\Hal\Extractor\LinkExtractor

LinkExtractor is responsible for extracting a link representation from Link instance.

ZF\Hal\Extractor\LinkCollectionExtractor

LinkCollectionExtractor is responsible for extracting a collection of Link instances. It also composes a LinkExtractor for extracting individual links.

Controller Plugins

ZF\Hal\Plugin\Hal (a.k.a. "Hal")

This class operates both as a view helper and as a controller plugin. It is responsible for providing controllers the facilities to generate HAL data models, as well as rendering relational links and HAL data structures.

View Layer

ZF\Hal\View\HalJsonModel

HalJsonModel is a view model that when used as the result of a controller service response signifies to the zf-hal module that the data within the model should be utilized to produce a JSON HAL representation.

ZF\Hal\View\HalJsonRenderer

HalJsonRenderer is a view renderer responsible for rendering HalJsonModel instances. In turn, this renderer will call upon the Hal plugin/view helper in order to transform the model content (an Entity or Collection) into a HAL representation.

ZF\Hal\View\HalJsonStrategy

HalJsonStrategy is responsible for selecting HalJsonRenderer when it identifies a HalJsonModel as the controller service response.