Fast JSON API

A lightning fast JSON:API serializer for Ruby Objects.

Performance Comparison

We compare serialization times with ActiveModelSerializer and alternative implementations as part of performance tests available at fast-jsonapi/comparisons.

We want to ensure that with every change on this library, serialization time stays significantly faster than the performance provided by the alternatives. Please read the performance article in the docs folder for any questions related to methodology.

Table of Contents

• Features
• Installation
• Usage
  • Rails Generator
  • Model Definition
  • Serializer Definition
  • Object Serialization
  • Compound Document
  • Key Transforms
  • Collection Serialization
  • Caching
  • Params
  • Conditional Attributes
  • Conditional Relationships
  • Specifying a Relationship Serializer
  • Sparse Fieldsets
  • Using helper methods
• Contributing

Features

• Declaration syntax similar to Active Model Serializer
• Support for belongs_to, has_many and has_one
• Support for compound documents (included)
• Optimized serialization of compound documents
• Caching

Installation

Add this line to your application's Gemfile:

gem 'fast_jsonapi', '~> 1.7.1', git: 'https://github.com/fast-jsonapi/fast_jsonapi'

Execute:

$ bundle install

Usage

Rails Generator

You can use the bundled generator if you are using the library inside of a Rails project:

rails g serializer Movie name year

This will create a new serializer in app/serializers/movie_serializer.rb

Model Definition

class Movie
  attr_accessor :id, :name, :year, :actor_ids, :owner_id, :movie_type_id
end

Serializer Definition

class MovieSerializer
  include FastJsonapi::ObjectSerializer
  set_type :movie  # optional
  set_id :owner_id # optional
  attributes :name, :year
  has_many :actors
  belongs_to :owner, record_type: :user
  belongs_to :movie_type
end

Sample Object

movie = Movie.new
movie.id = 232
movie.name = 'test movie'
movie.actor_ids = [1, 2, 3]
movie.owner_id = 3
movie.movie_type_id = 1
movie

movies =
  2.times.map do |i|
    m = Movie.new
    m.id = i + 1
    m.name = "test movie #{i}"
    m.actor_ids = [1, 2, 3]
    m.owner_id = 3
    m.movie_type_id = 1
    m
  end

Object Serialization

Return a hash

hash = MovieSerializer.new(movie).serializable_hash

Return Serialized JSON

json_string = MovieSerializer.new(movie).serializable_hash.to_json

Serialized Output

{
  "data": {
    "id": "3",
    "type": "movie",
    "attributes": {
      "name": "test movie",
      "year": null
    },
    "relationships": {
      "actors": {
        "data": [
          {
            "id": "1",
            "type": "actor"
          },
          {
            "id": "2",
            "type": "actor"
          }
        ]
      },
      "owner": {
        "data": {
          "id": "3",
          "type": "user"
        }
      }
    }
  }
}

Key Transforms

By default fast_jsonapi underscores the key names. It supports the same key transforms that are supported by AMS. Here is the syntax of specifying a key transform

class MovieSerializer
  include FastJsonapi::ObjectSerializer
  # Available options :camel, :camel_lower, :dash, :underscore(default)
  set_key_transform :camel
end

Here are examples of how these options transform the keys

set_key_transform :camel # "some_key" => "SomeKey"
set_key_transform :camel_lower # "some_key" => "someKey"
set_key_transform :dash # "some_key" => "some-key"
set_key_transform :underscore # "some_key" => "some_key"

Attributes

Attributes are defined in FastJsonapi using the attributes method. This method is also aliased as attribute, which is useful when defining a single attribute.

By default, attributes are read directly from the model property of the same name. In this example, name is expected to be a property of the object being serialized:

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  attribute :name
end

Custom attributes that must be serialized but do not exist on the model can be declared using Ruby block syntax:

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  attributes :name, :year

  attribute :name_with_year do |object|
    "#{object.name} (#{object.year})"
  end
end

The block syntax can also be used to override the property on the object:

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  attribute :name do |object|
    "#{object.name} Part 2"
  end
end

Attributes can also use a different name by passing the original method or accessor with a proc shortcut:

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  attributes :name

  attribute :released_in_year, &:year
end

Links Per Object

Links are defined in FastJsonapi using the link method. By default, links are read directly from the model property of the same name. In this example, public_url is expected to be a property of the object being serialized.

You can configure the method to use on the object for example a link with key self will get set to the value returned by a method called url on the movie object.

You can also use a block to define a url as shown in custom_url. You can access params in these blocks as well as shown in personalized_url

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  link :public_url

  link :self, :url

  link :custom_url do |object|
    "http://movies.com/#{object.name}-(#{object.year})"
  end

  link :personalized_url do |object, params|
    "http://movies.com/#{object.name}-#{params[:user].reference_code}"
  end
end

Links on a Relationship

You can specify relationship links by using the links: option on the serializer. Relationship links in JSON API are useful if you want to load a parent document and then load associated documents later due to size constraints (see related resource links)

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  has_many :actors, links: {
    self: :url,
    related: -> (object) {
      "https://movies.com/#{object.id}/actors"
    }
  }
end

Relationship links can also be configured to be defined as a method on the object.

  has_many :actors, links: :actor_relationship_links

This will create a self reference for the relationship, and a related link for loading the actors relationship later. NB: This will not automatically disable loading the data in the relationship, you'll need to do that using the lazy_load_data option:

  has_many :actors, lazy_load_data: true, links: {
    self: :url,
    related: -> (object) {
      "https://movies.com/#{object.id}/actors"
    }
  }

Meta Per Resource

For every resource in the collection, you can include a meta object containing non-standard meta-information about a resource that can not be represented as an attribute or relationship.

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  meta do |movie|
    {
      years_since_release: Date.current.year - movie.year
    }
  end
end

Compound Document

Support for top-level and nested included associations through options[:include].

options = {}
options[:meta] = { total: 2 }
options[:links] = {
  self: '...',
  next: '...',
  prev: '...'
}
options[:include] = [:actors, :'actors.agency', :'actors.agency.state']
MovieSerializer.new(movies, options).serializable_hash.to_json

Collection Serialization

options[:meta] = { total: 2 }
options[:links] = {
  self: '...',
  next: '...',
  prev: '...'
}
hash = MovieSerializer.new(movies, options).serializable_hash
json_string = MovieSerializer.new(movies, options).serializable_hash.to_json

Control Over Collection Serialization

You can use is_collection option to have better control over collection serialization.

If this option is not provided or nil autodetect logic is used to try understand if provided resource is a single object or collection.

Autodetect logic is compatible with most DB toolkits (ActiveRecord, Sequel, etc.) but cannot guarantee that single vs collection will be always detected properly.

options[:is_collection]

was introduced to be able to have precise control this behavior

• nil or not provided: will try to autodetect single vs collection (please, see notes above)
• true will always treat input resource as collection
• false will always treat input resource as single object

Caching

To enable caching, use cache_options store: <cache_store>:

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  # use rails cache with a separate namespace and fixed expiry
  cache_options store: Rails.cache, namespace: 'fast-jsonapi', expires_in: 1.hour
end

store is required can be anything that implements a #fetch(record, **options, &block) method:

• record is the record that is currently serialized
• options is everything that was passed to cache_options except store, so it can be everyhing the cache store supports
• &block should be executed to fetch new data if cache is empty

So for the example above, FastJsonapi will call the cache instance like this:

Rails.cache.fetch(record, namespace: 'fast-jsonapi, expires_in: 1.hour) { ... }

Params

In some cases, attribute values might require more information than what is available on the record, for example, access privileges or other information related to a current authenticated user. The options[:params] value covers these cases by allowing you to pass in a hash of additional parameters necessary for your use case.

Leveraging the new params is easy, when you define a custom id, attribute or relationship with a block you opt-in to using params by adding it as a block parameter.

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  set_id do |movie, params|
    # in here, params is a hash containing the `:admin` key
    params[:admin] ? movie.owner_id : "movie-#{movie.id}"
  end

  attributes :name, :year
  attribute :can_view_early do |movie, params|
    # in here, params is a hash containing the `:current_user` key
    params[:current_user].is_employee? ? true : false
  end

  belongs_to :primary_agent do |movie, params|
    # in here, params is a hash containing the `:current_user` key
    params[:current_user].is_employee? ? true : false
  end
end

# ...
current_user = User.find(cookies[:current_user_id])
serializer = MovieSerializer.new(movie, {params: {current_user: current_user}})
serializer.serializable_hash

Custom attributes and relationships that only receive the resource are still possible by defining the block to only receive one argument.

Conditional Attributes

Conditional attributes can be defined by passing a Proc to the if key on the attribute method. Return true if the attribute should be serialized, and false if not. The record and any params passed to the serializer are available inside the Proc as the first and second parameters, respectively.

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  attributes :name, :year
  attribute :release_year, if: Proc.new { |record|
    # Release year will only be serialized if it's greater than 1990
    record.release_year > 1990
  }

  attribute :director, if: Proc.new { |record, params|
    # The director will be serialized only if the :admin key of params is true
    params && params[:admin] == true
  }
end

# ...
current_user = User.find(cookies[:current_user_id])
serializer = MovieSerializer.new(movie, { params: { admin: current_user.admin? }})
serializer.serializable_hash

Conditional Relationships

Conditional relationships can be defined by passing a Proc to the if key. Return true if the relationship should be serialized, and false if not. The record and any params passed to the serializer are available inside the Proc as the first and second parameters, respectively.

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  # Actors will only be serialized if the record has any associated actors
  has_many :actors, if: Proc.new { |record| record.actors.any? }

  # Owner will only be serialized if the :admin key of params is true
  belongs_to :owner, if: Proc.new { |record, params| params && params[:admin] == true }
end

# ...
current_user = User.find(cookies[:current_user_id])
serializer = MovieSerializer.new(movie, { params: { admin: current_user.admin? }})
serializer.serializable_hash

Specifying a Relationship Serializer

In many cases, the relationship can automatically detect the serializer to use.

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  # resolves to StudioSerializer
  belongs_to :studio
  # resolves to ActorSerializer
  has_many :actors
end

At other times, such as when a property name differs from the class name, you may need to explicitly state the serializer to use. You can do so by specifying a different symbol or the serializer class itself (which is the recommended usage):

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  # resolves to MovieStudioSerializer
  belongs_to :studio, serializer: :movie_studio
  # resolves to PerformerSerializer
  has_many :actors, serializer: PerformerSerializer
end

For more advanced cases, such as polymorphic relationships and Single Table Inheritance, you may need even greater control to select the serializer based on the specific object or some specified serialization parameters. You can do by defining the serializer as a Proc:

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  has_many :actors, serializer: Proc.new do |record, params|
    if record.comedian?
      ComedianSerializer
    elsif params[:use_drama_serializer]
      DramaSerializer
    else
      ActorSerializer
    end
  end
end

Sparse Fieldsets

Attributes and relationships can be selectively returned per record type by using the fields option.

class MovieSerializer
  include FastJsonapi::ObjectSerializer

  attributes :name, :year
end

serializer = MovieSerializer.new(movie, { fields: { movie: [:name] } })
serializer.serializable_hash

Using helper methods

You can mix-in code from another ruby module into your serializer class to reuse functions across your app.

Since a serializer is evaluated in a the context of a class rather than an instance of a class, you need to make sure that your methods act as class methods when mixed in.

Using ActiveSupport::Concern

module AvatarHelper
  extend ActiveSupport::Concern

  class_methods do
    def avatar_url(user)
      user.image.url
    end
  end
end

class UserSerializer
  include FastJsonapi::ObjectSerializer

  include AvatarHelper # mixes in your helper method as class method

  set_type :user

  attributes :name, :email

  attribute :avatar do |user|
    avatar_url(user)
  end
end

Using Plain Old Ruby

module AvatarHelper
  def avatar_url(user)
    user.image.url
  end
end

class UserSerializer
  include FastJsonapi::ObjectSerializer

  extend AvatarHelper # mixes in your helper method as class method

  set_type :user

  attributes :name, :email

  attribute :avatar do |user|
    avatar_url(user)
  end
end

Customizable Options

Option	Purpose	Example
set_type	Type name of Object	set_type :movie
key	Key of Object	belongs_to :owner, key: :user
set_id	ID of Object	set_id :owner_id or set_id { |record, params| params[:admin] ? record.id : "#{record.name.downcase}-#{record.id}" }
cache_options	Hash with store to enable caching and optional further cache options	cache_options store: ActiveSupport::Cache::MemoryStore.new, expires_in: 5.minutes
id_method_name	Set custom method name to get ID of an object (If block is provided for the relationship, id_method_name is invoked on the return value of the block instead of the resource object)	has_many :locations, id_method_name: :place_ids
object_method_name	Set custom method name to get related objects	has_many :locations, object_method_name: :places
record_type	Set custom Object Type for a relationship	belongs_to :owner, record_type: :user
serializer	Set custom Serializer for a relationship	has_many :actors, serializer: :custom_actor, has_many :actors, serializer: MyApp::Api::V1::ActorSerializer, or has_many :actors, serializer -> (object, params) { (return a serializer class) }
polymorphic	Allows different record types for a polymorphic association	has_many :targets, polymorphic: true
polymorphic	Sets custom record types for each object class in a polymorphic association	has_many :targets, polymorphic: { Person => :person, Group => :group }

Instrumentation

fast_jsonapi also has builtin Skylight integration. To enable, add the following to an initializer:

require 'fast_jsonapi/instrumentation/skylight'

Skylight relies on ActiveSupport::Notifications to track these two core methods. If you would like to use these notifications without using Skylight, simply require the instrumentation integration:

require 'fast_jsonapi/instrumentation'

The two instrumented notifications are supplied by these two constants:

• FastJsonapi::ObjectSerializer::SERIALIZABLE_HASH_NOTIFICATION
• FastJsonapi::ObjectSerializer::SERIALIZED_JSON_NOTIFICATION

It is also possible to instrument one method without the other by using one of the following require statements:

require 'fast_jsonapi/instrumentation/serializable_hash'
require 'fast_jsonapi/instrumentation/serialized_json'

Same goes for the Skylight integration:

require 'fast_jsonapi/instrumentation/skylight/normalizers/serializable_hash'
require 'fast_jsonapi/instrumentation/skylight/normalizers/serialized_json'

Running Tests

The project has and requires unit tests, functional tests and performance tests. To run tests use the following command:

rspec

Contributing

Please follow the instructions we provide as part of the issue and pull request creation processes.

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.