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This library provides a framework-agnostic interface for generating HAL+JSON representations of resources in Ruby.


Add this line to your application's Gemfile:

gem 'halogen'

And then execute:

$ bundle

Or install it yourself as:

$ gem install halogen


Basic usage

Create a simple representer class and include Halogen:

class GoatRepresenter
  include Halogen

  property :name do

  link :self do


repr = GoatRepresenter.new

Then call repr.render:

  name: 'Gideon',
  _links: {
    self: { href: '/goats/gideon' }

Or repr.to_json:

'{"name": "Gideon", "_links": {"self": {"href": "/goats/gideon"}}}'

Representer types

1. Simple

Not associated with any particular resource or collection. For example, an API entry point:

class ApiRootRepresenter
  include Halogen

  link(:self) { '/api' }

2. Resource

Represents a single item:

class GoatRepresenter
  include Halogen

  resource :goat

When a resource is declared, #initialize expects the resource as the first argument:

repr = GoatRepresenter.new(Goat.new, ...)

This makes property definitions cleaner:

property :name # now calls Goat#name by default

3. Collection

Represents a collection of items. When a collection is declared, the embedded resource with the same name will always be embedded, whether it is requested via standard embed options or not.

class GoatKidsRepresenter
  include Halogen

  collection :kids

  embed(:kids) { ... } # always embedded

Defining properties, links and embeds

Properties can be defined in several ways:

property(:age) { "#{goat.age} years old" }
property :age # => Goat#age, if resource is declared
property :age do
property(:age) { calculate_age }

def calculate_age


The inclusion of properties can be determined by conditionals using if and unless options. For example, with a method name:

property :age, if: :include_age?

def include_age?
  goat.age < 10

With a proc:

property :age, unless: proc { goat.age.nil? }, value: ...

For links and embeds:

link :kids, :templated, unless: :exclude_kids_link?, value: ...
embed :kids, if: proc { goat.kids.size > 0 } do


Simple link:

link(:root) { '/' }
# => { _links: { root: { href: '/' } } ... }

Templated link:

link(:find, :templated) { '/goats/{?id}' }
# => { _links: { find: { href: '/goats/{?id}', templated: true } } ... }

Embedded resources

Embedded resources are not rendered by default. They will be included if both of the following conditions are met:

  1. The proc returns either a Halogen instance or an array of Halogen instances
  2. The embed is requested via the parent representer's options, e.g.:
GoatRepresenter.new(embed: { kids: true, parents: false })

Embedded resources can be nested to any depth, e.g.:

GoatRepresenter.new(embed: {
  kids: {
    foods: {
      ingredients: true
    pasture: true

Using with Rails

If Halogen is loaded in a Rails application, Rails url helpers will be available in representers:

link(:new) { new_goat_url }

More examples

What's with the goat?

It is majestic.


  1. Fork it ( https://github.com/mode/halogen/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request