Table of Contents

• Grape::ActiveModelSerializers
  • Installation
  • Dependencies
  • Usage
    • Require grape-active_model_serializers
    • Tell your API to use Grape::Formatter::ActiveModelSerializers
    • Writing Serializers
    • Serializers are inferred by active_record model names
    • Array Roots
    • API Versioning
    • Manually specifying serializer / adapter options
    • Custom Metadata
    • Default Serializer Options
    • Current User
    • Full Example
  • Contributing
  • History

Grape::ActiveModelSerializers

Use active_model_serializers with Grape!

Installation

Add the grape and grape-active_model_serializers gems to Gemfile and run bundle install.

gem 'grape-active_model_serializers'

See UPGRADING if you're upgrading from a previous version.

Dependencies

• >= Ruby v3.1
• >= grape v2.3.0
• >= active_model_serializers v0.10.0

Usage

Require grape-active_model_serializers

# config.ru
require 'grape-active_model_serializers'

Tell your API to use Grape::Formatter::ActiveModelSerializers

class API < Grape::API
  format :json
  formatter :json, Grape::Formatter::ActiveModelSerializers

  # Serializes errors with ActiveModel::Serializer::ErrorSerializer if an ActiveModel.
  # Serializer conforms to the adapter, ex: json, jsonapi.
  # So an error formatted with a jsonapi formatter would render as per:
  # http://jsonapi.org/format/#error-objects
  error_formatter :json, Grape::Formatter::ActiveModelSerializers
end

Writing Serializers

See active_model_serializers

Serializers are inferred by active_record model names

grape-active_model_serializers will search for serializers for the objects returned by your grape API.

namespace :users do
  get ":id" do
    @user = User.find(params[:id])
  end
end

In this case, as User objects are being returned, grape-active_model_serializers will look for a serializer named UserSerializer.

Array Roots

When serializing an array, the array root is set to the innermost namespace name if there is one, otherwise it is set to the route name.

In the following API the array root is users.

namespace :users do
  get ":id" do
    @user = User.find(params[:id])
  end
end

In the following example the array root is people.

get "people" do
  @user = User.all
end

API Versioning

If your Grape API is versioned you must namespace your serializers accordingly.

For example, given the following API.

module CandyBar
  class Core < Grape::API
    version 'candy_bar', using: :header, vendor: 'acme'
  end
end

module Chocolate
  class Core < Grape::API
    version 'chocolate', using: :header, vendor: 'acme'
  end
end

class API < Grape::API
  format :json
  formatter :json, Grape::Formatter::ActiveModelSerializers

  mount CandyBar::Core
  mount Chocolate::Core
end

Namespace your serializers according to each version.

module CandyBar
  class UserSerializer < ActiveModel::Serializer
    attributes :first_name, :last_name, :email
  end
end

module Chocolate
  class UserSerializer < ActiveModel::Serializer
    attributes :first_name, :last_name
  end
end

This keeps serializers organized.

app
└── api
    ├── chocolate
        └── core.rb
    └── candy_bar
        └── core.rb
    api.rb
└── serializers
    ├── chocolate
        └── user_serializer.rb
    └── candy_bar
        └── user_serializer.rb

Or as follows.

└── serializers
    ├── chocolate_user_serializer.rb
    └── candy_bar_user_serializer.rb

ActiveModelSerializer will fetch automatically the right serializer to render.

Manually specifying serializer / adapter options

# Serializer and adapter options can be specified on routes or namespaces.
namespace 'foo', serializer: BarSerializer do
  get "/" do
    # will use "bar" serializer
  end

  # Options specified on a route or namespace override those of the containing namespace.
  get "/home", serializer: HomeSerializer do
    # will use "home" serializer
  end

  # All standard options for `ActiveModel::Serializers` are supported.
  get "/fancy_homes", root: 'world', each_serializer: FancyHomesSerializer
  ...
  end
end

# Serializer and adapter options can also be specified in the body of the route
resource :users do
  get '/:id' do
    if conditional
      # uses UserSerializer and configured default adapter automatically
      current_user
    else
      # uses specified serializer and adapter
      render current_user, serializer: ErrorSerializer, adapter: :attributes
    end
  end
end

# Adhoc serializer options can be specified in the body of the route
resource :users do
  get '/:id' do
    render current_user, extra: { adhoc_name_option: 'value' }
  end
end

class UserSerializer
  def name
    instance_options[:adhoc_name_option] # accessible in instance_options
  end
end

Custom Metadata

# Control any additional metadata using meta and meta_key
get "/homes"
  collection = Home.all
  render collection, { meta: { page: 5, current_page: 3 }, meta_key: :pagination_info }
end

Default Serializer Options

helpers do
  def default_serializer_options
    { only: params[:only], except: params[:except] }
  end
end

Current User

One of the nice features of ActiveModel::Serializers is that it provides access to the authorization context via the current_user.

In Grape, you can get the same behavior by defining a current_user helper method.

helpers do
  def current_user
    @current_user ||= User.where(access_token: params[:token]).first
  end

  def authenticate!
    error!('401 Unauthenticated', 401) unless current_user
  end
end

Then, in your serializer, you could show or hide some elements based on the current user's permissions.

class PostSerializer < ActiveModel::Serializer
  def include_admin_comments?
    current_user.roles.member? :admin
  end
end

Note: in the 0.9.x stable version of active model serializers, you have to access current user on scope - so scope.current_user.

Full Example

class User < ActiveRecord::Base
  attr_accessor :first_name, :last_name, :password, :email
end

class UserSerializer < ActiveModel::Serializer
  attributes :first_name, :last_name
end

class API < Grape::API
  get("/home") do
    User.new({first_name: 'JR', last_name: 'HE', email: 'contact@jrhe.co.uk'})
  end
end

API.new.get "/home" # => '{ user: { first_name: "JR", last_name: "HE" } }'

Contributing

See CONTRIBUTING.

History

Structured and based upon grape-rabl.