Representable

Representable maps Ruby objects to documents and back.

In other words: Take an object and decorate it with a representer module. This will allow you to render a JSON, XML or YAML document from that object. But that's only half of it! You can also use representers to parse a document and create or populate an object.

Representable is helpful for all kind of mappings, rendering and parsing workflows. However, it is mostly useful in API code. Are you planning to write a real REST API with representable? Then check out the Roar gem first, save work and time and make the world a better place instead.

Representable comes with a rich set of options and semantics for parsing and rendering documents. Its full documentation can be found on the Trailblazer site.

What if we're writing an API for music - songs, albums, bands.

class Song < OpenStruct
end

song = Song.new(title: "Fallout", track: 1)

Representations are defined using representer classes, called _decorator, or modules.

In these examples, let's use decorators

class SongRepresenter < Representable::Decorator
  include Representable::JSON

  property :title
  property :track
end

In the representer the #property method allows declaring represented attributes of the object. All the representer requires for rendering are readers on the represented object, e.g. #title and #track. When parsing, it will call setters - in our example, that'd be #title= and #track=.

Mixing in the representer into the object adds a rendering method.

SongRepresenter.new(song).to_json
#=> {"title":"Fallout","track":1}

It also adds support for parsing.

song = SongRepresenter.new(song).from_json(%{ {"title":"Roxanne"} })
#=> #<Song title="Roxanne", track=nil>

Note that parsing hashes per default does require string keys and does not pick up symbol keys.

Let's add a list of composers to the song representation.

class SongRepresenter < Representable::Decorator
  include Representable::JSON

  property :title
  property :track
  collection :composers
end

Surprisingly, #collection lets us define lists of objects to represent.

Song.new(title: "Fallout", composers: ["Stewart Copeland", "Sting"]).
  extend(SongRepresenter).to_json

#=> {"title":"Fallout","composers":["Stewart Copeland","Sting"]}

And again, this works both ways - in addition to the title it extracts the composers from the document, too.

Representers can also manage compositions. Why not use an album that contains a list of songs?

class Album < OpenStruct
end

album = Album.new(name: "The Police", songs: [song, Song.new(title: "Synchronicity")])

Here comes the representer that defines the composition.

class AlbumRepresenter < Representable::Decorator
  include Representable::JSON

  property :name
  collection :songs, decorator: SongRepresenter, class: Song
end

If you don't want to maintain two separate modules when nesting representations you can define the SongRepresenter inline.

class AlbumRepresenter < Representable::Decorator
  include Representable::JSON

  property :name

  collection :songs, class: Song do
    property :title
    property :track
    collection :composers
  end
end

Representable has many more features and can literally parse and render any kind of document to an arbitrary Ruby object graph.

Please check the official documentation for more.

The representable gem runs with all Ruby versions >= 2.4.0. t

gem 'representable'

Representable does a great job with JSON, it also features support for XML, YAML and pure ruby hashes. But Representable did not bundle dependencies for JSON and XML.

If you want to use JSON, add the following to your Gemfile:

gem 'multi_json'

If you want to use XML, add the following to your Gemfile:

gem 'nokogiri'

Representable started as a heavily simplified fork of the ROXML gem. Big thanks to Ben Woosley for his extremely inspiring work.

• Copyright (c) 2011-2020 Nick Sutterer apotonick@gmail.com
• ROXML is Copyright (c) 2004-2009 Ben Woosley, Zak Mandhro and Anders Engstrom.

Representable is released under the MIT License.