Halogen

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

Installation

Add this line to your application's Gemfile:

gem 'halogen'

And then execute:

$ bundle

Or install it yourself as:

$ gem install halogen

Usage

Basic usage

Create a simple representer class and include Halogen:

class GoatRepresenter
  include Halogen

  property :name do
    'Gideon'
  end

  link :self do
    '/goats/gideon'
  end
end

Instantiate:

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' }
end

2. Resource

Represents a single item:

class GoatRepresenter
  include Halogen

  resource :goat
end

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
end

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
  goat.age.round
end

property(:age) { calculate_age }

def calculate_age
  ...
end

Conditionals

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
end

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
  ...
end

Links

Simple link:

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

Templated link:

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

Optional links:

representer = MyRepresenterWithManyLinks.new(include_links: false)
representation = representer.render
representation[:_links] #nil

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

• Full representer class
• Extensions

What's with the goat?

It is majestic.

Contributing

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