Serializr

Serializr is a library for creating canonical JSON representation of objects for your RESTful APIs.

Think of the serializers as the view layer of your application. They are not the only JSON representation of an object, but they are the representation you wanna show to the API.

Add this line to your application's Gemfile:

gem 'serializr'

Using the serializr library is pretty simple. To generate your first serializer, execute:

$ rails generate serializr User id name email

The output should hint that the generator created two files:

create  app/serializers/application_serializer.rb
create  app/serializers/user_serializer.rb

The app/serializers/user_serializer.rb file should contain:

class UserSerializer < ApplicationSerializer
  attributes :id, :name, :email
end

This says: expect the object to be serialized to respond to #id, #name and #email and show the resulting JSON as:

{
  "id": 42,
  "name": "John Doe",
  "email": "john@nsa.gov"
}

Oh, wait... Your users don't respond to #name?

class UserSerializer < ApplicationSerializer
  attributes :id, :name, :email

  def name
    "#{object.first_name} #{object.last_name}"
  end
end

That's fine. Your serializers can render fields your object don't respond to.

Now, to render the JSON object, you need to say the following in your controller:

class UsersController < ApplicationController
  def show
    user = User.find(params[:id])

    render json: user
  end
end

The serializr library hooks itself into ActionController::Base or ActionController::API and it can infer the UserSerializer out of the User object. You can also be explicit, in which case the inferring logic won't be triggered at all.

class UsersController < ApplicationController
  def show
    user = User.find(params[:id])

    render json: user, serializer: UserSerializer
  end
end

You can also render collections of objects:

class FriendsController < ApplicationController
  def index
    friends = User.friends_of(params[:id])

    render json: friends
  end
end

Being explicit here may have performance benefits, as to guess the Serializer class to use, we need to unroll the collection. The explicit usage, unarguably, looks pretty awesome as well, so you can wow your friends! Which, is always cool, you know. 😎

class FriendsController < ApplicationController
  def index
    friends = User.friends_of(params[:id])

    render json: friends, serializer: UserSerializer[]
  end
end

And this is how you drop Action View off your API's, kids!

To fill the API cliché, we need to go over one last file: app/serializers/application_serializer.rb. At first, it looks like this:

class ApplicationSerializer < Serializr
end

The grown ups call it Layer Supertype. We'll call it that thing that looks like ApplicationController and serves the same purpose, but for the serializers, not the controllers. You can use it to put common utilities shared by all the serializers.

For example:

class ApplicationSerializer < Serializr
  # You may need the routes helpers, so you can link between resources in your
  # JSON responses.
  include Rails.application.routes.url_helpers

  cattr_reader :serializer_class_cache do
    Hash.new do |hash, cls|
      hash[cls] = "#{cls}Serializer".constantize
    end
  end

  # Because I'm sure you gonna ask: how do I render associations. Where are the
  # `has_one` and `has_many` class macros?
  #
  # The answers is: you don't need those macros. You can use similar methods
  # like the ones below to render the associations with plain old boring Ruby
  # methods.
  #
  # class UserSerializer < ApplicationSerializer
  #   attributes :card
  #
  #   def card
  #     render_one(object.credit_card)
  #   end
  # end
  #
  # No extra DSL, but still: clean, consise and flexible view code.
  def render_one(object, serializer: nil)
    return if object.nil?

    serializer ||= serializer_class_cache[object.class]
    serializer.new(object)
  end

  def render_many(objects, serializer: nil)
    return [] if objects.blank?

    serializer ||= serializer_class_cache[objects.first.class][]
    serializer.new(objects)
  end
end

Serializr? Really? I know. It's fine.

You can require serializr, you can require serializer as well. The constants? Both of Serializr and Serializer point to the same thing. Same for the generators. Use whatever your brain and 🖐 (fingers) like.

Bug reports and pull requests are welcome on GitHub at https://github.com/gsamokovarov/serializr. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.