faceted
Faceted provides a set of tools, patterns, and modules for use in API implementations.
It was originally written for Trunk Club and is maintained by Coraline Ada Ehmke (@bantik) and Max Thom Stahl (@villainous).
Presenters
Let's say that you have an ActiveRecord model called Musician, and you want to expose it through your API using a Presenter pattern. Faceted makes it easy. Create a new class namespaced inside of your API like so:
module MyApi
class Musician
include Faceted::Presenter
presents :musician
field :name
field :genre
field :instrument, :default => 'guitar'
end
end
That's actually all you have to do. The presents
method maps your Musician presenter to a root-level class called Musician
, and the field
methods map to attributes or methods on the associated AR Musician instance. If a default is set for a field, that default value will be stored when the presenter is used to create a record, unless overridden.
What's that, you say? How is the appropriate AR Musican record associated? Simple. Invoke an instance of the MyApi::Musician
passing in an :id
parameter, and it just works:
m = Musician.create(:name => 'Johnny Cash', :genre => 'Western')
m.id
=> 13
presenter = MyApi::Musician.new(:id => 13)
presenter.name
=> "Johnny Cash"
You can also invoke methods on AR instances using the same syntax. Let's say that your base Musician
class has a random_song_title
method that returns one of the musician's popular songs. Simply wire up the method in your presenter:
field :random_song_title
That's it.
presenter.random_song_title
=> "Ring of Fire"
Relationships work almost the same way. If Musician
actually has_one
birthplace, and includes a birthplace_id
attribute, wire it up like this:
field :birthplace_id
Create a presenter for the associated Birthplace model:
module MyApi
class Birthplace
include Faceted::Presenter
presents :birthplace
field :city
field :state
end
end
Now your Musician
presenter responds the way it should:
presenter.birthplace.city
=> "Kingsland"
It's smart enough to identify that birthplace_id
indicates a relationship and builds the association for you. If you don't want it to do this, simply pass the skip_association
flag:
field :record_label_id, :skip_association => true
You can also explicitly declare the class of the association:
field :genre_id, :class_name => 'MusicalGenre'
Presenters from Existing Models
In your controllers, you will typically be using one of three methods to instantiate a presenter: new
, materialize
, or from
.
new
This method is used to retrieve and instantiate a persisted model based on an id
:
m = Musician.create(:name => 'Bauhaus', :genre => 'Goth') m.id
=> 213
presenter = MyApi::Musician.new(:id => 213)
presenter.name
=> "Bauhaus"
materialize
Have an array of objects that you need translated into presenters? No problem. Use the materialize
class method on the presenter class:
musicians = [
::Musician.new(:name => 'Love and Rockets'),
::Musician.new(:name => 'The Pixies')
]
presenters = MyApi::Musician.materialize(musicians)
presenters.first.name
=> 'Love and Rockets'
from
If you have an single instance of a persisted model already loaded, or if you're presenting a class that does not get read from a database (e.g. an object from an API response), you can use the from
class method to materialize a single presenter object:
musician_from_json_response = ::Musician.new(:name => 'Dust and a Shadow')
presenter = MyApi::Musician.from(musician_from_json_response)
presenter.name
=> 'Dust and a Shadow'
Collectors
Collectors are simply models that collect multiple instances of another model. An example:
module MyApi
class Playlist
include Faceted::Collector
collects :musicians, :find_by => :genre_id
collects :deejays #implicit find_by, using 'playlist_id'
end
end
l = MyApi::Playlist.new(:genre_id => 3)
l.musicians.count
=> 14
l.musicians.first.name
=> "American Music Club"
Controllers
Wiring up your controllers is easy. Start with your base controller:
class MyApi::BaseController < ActionController::Base
require 'faceted'
include Faceted::Controller
before_filter :authenticate_user!
respond_to :json
rescue_from Exception, :with => :render_500
rescue_from ActiveRecord::RecordNotFound, :with => :render_404
end
Then create the controllers for your API-specific models:
class MyApi::MusiciansController < MyApi::BaseController
def show
@musician = MyApi::Musician.new(params)
render_response @musician
end
def update
@musician = MyApi::Musician.new(params)
@musician.save
render_response @musician
end
end
Contributing to faceted
- Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet.
- Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it.
- Fork the project.
- Start a feature/bugfix branch.
- Commit and push until you are happy with your contribution.
- Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
- Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.
Copyright
Copyright (c) 2012 Trunk Club. See LICENSE.txt for further details.