JSONAPI::Serializers

JSONAPI::Serializers is a simple library for serializing Ruby objects and their relationships into the JSON:API format.

This library is up-to-date with the finalized v1 JSON API spec.

• Features
• Installation
• Usage
  • Configuration
  • Define a serializer
  • Serialize an object
  • Serialize a collection
  • Null handling
  • Multiple attributes
  • Custom attributes
  • More customizations
  • Base URL
  • Root metadata
  • Root links
  • Root errors
  • Root jsonapi object
  • Explicit serializer discovery
  • Namespace serializers
  • Sparse fieldsets
• Relationships
  • Compound documents and includes
  • Relationship path handling
  • Control links and data in relationships
• Rails example
• Sinatra example
• Unfinished business
• Contributing

Features

• Works with any Ruby web framework, including Rails, Sinatra, etc. This is a pure Ruby library.
• Supports the readonly features of the JSON:API spec.
  • Full support for compound documents ("side-loading") and the include parameter.
• Similar interface to ActiveModel::Serializers, should provide an easy migration path.
• Intentionally unopinionated and simple, allows you to structure your app however you would like and then serialize the objects at the end. Easy to integrate with your existing authorization systems and service objects.

JSONAPI::Serializers was built as an intentionally simple serialization interface. It makes no assumptions about your database structure or routes and it does not provide controllers or any create/update interface to the objects. It is a library, not a framework. You will probably still need to do work to make your API fully compliant with the nuances of the JSON:API spec, for things like supporting /relationships routes and for supporting write actions like creating or updating objects. If you are looking for a more complete and opinionated framework, see the jsonapi-resources project.

Installation

Add this line to your application's Gemfile:

gem 'jsonapi-serializers'

Or install directly with gem install jsonapi-serializers.

Usage

Configuration

The following configuration options can be set on JSONAPI::Serializer.config, preferably inside an initializer.

key_transform

Option	Result
:camel	ExampleKey
:camel_lower	exampleKey
:dash	example-key (default)
:unaltered	the original, unaltered key
:underscore	example_key
nil	use the default (:dash) transformation

JSONAPI::Serializer.config.key_transform = :unaltered

Define a serializer

require 'jsonapi-serializers'

class PostSerializer
  include JSONAPI::Serializer

  attribute :title
  attribute :content
end

Serialize an object

JSONAPI::Serializer.serialize(post)

Returns a hash:

{
  "data": {
    "id": "1",
    "type": "posts",
    "attributes": {
      "title": "Hello World",
      "content": "Your first post"
    },
    "links": {
      "self": "/posts/1"
    }
  }
}

Serialize a collection

JSONAPI::Serializer.serialize(posts, is_collection: true)

Returns:

{
  "data": [
    {
      "id": "1",
      "type": "posts",
      "attributes": {
        "title": "Hello World",
        "content": "Your first post"
      },
      "links": {
        "self": "/posts/1"
      }
    },
    {
      "id": "2",
      "type": "posts",
      "attributes": {
        "title": "Hello World again",
        "content": "Your second post"
      },
      "links": {
        "self": "/posts/2"
      }
    }
  ]
}

You must always pass is_collection: true when serializing a collection, see Null handling.

Null handling

JSONAPI::Serializer.serialize(nil)

Returns:

{
  "data": null
}

And serializing an empty collection:

JSONAPI::Serializer.serialize([], is_collection: true)

Returns:

{
  "data": []
}

Note that the JSON:API spec distinguishes in how null/empty is handled for single objects vs. collections, so you must always provide is_collection: true when serializing multiple objects. If you attempt to serialize multiple objects without this flag (or a single object with it on) a JSONAPI::Serializer::AmbiguousCollectionError will be raised.

Multiple attributes

You could declare multiple attributes at once:

 attributes :title, :body, :contents

Custom attributes

By default the serializer looks for the same name of the attribute on the object it is given. You can customize this behavior by providing a block to attribute, has_one, or has_many:

  attribute :content do
    object.body
  end

  has_one :comment do
    Comment.where(post: object).take!
  end

  has_many :authors do
    Author.where(post: object)
  end

The block is evaluated within the serializer instance, so it has access to the object and context instance variables.

More customizations

Many other formatting and customizations are possible by overriding any of the following instance methods on your serializers.

# Override this to customize the JSON:API "id" for this object.
# Always return a string from this method to conform with the JSON:API spec.
def id
  object.slug.to_s
end

# Override this to customize the JSON:API "type" for this object.
# By default, the type is the object's class name lowercased, pluralized, and dasherized,
# per the spec naming recommendations: http://jsonapi.org/recommendations/#naming
# For example, 'MyApp::LongCommment' will become the 'long-comments' type.
def type
  'long-comments'
end

# Override this to customize how attribute names are formatted.
# By default, attribute names are dasherized per the spec naming recommendations:
# http://jsonapi.org/recommendations/#naming
def format_name(attribute_name)
  attribute_name.to_s.dasherize
end

# The opposite of format_name. Override this if you override format_name.
def unformat_name(attribute_name)
  attribute_name.to_s.underscore
end

# Override this to provide resource-object metadata.
# http://jsonapi.org/format/#document-structure-resource-objects
def meta
end

# Override this to set a base URL (http://example.com) for all links. No trailing slash.
def base_url
  @base_url
end

# Override this to provide a resource-object jsonapi object containing the version in use.
# http://jsonapi.org/format/#document-jsonapi-object
def jsonapi
end

def self_link
  "#{base_url}/#{type}/#{id}"
end

def relationship_self_link(attribute_name)
  "#{self_link}/relationships/#{format_name(attribute_name)}"
end

def relationship_related_link(attribute_name)
  "#{self_link}/#{format_name(attribute_name)}"
end

If you override self_link, relationship_self_link, or relationship_related_link to return nil, the link will be excluded from the serialized object.

Base URL

You can override the base_url instance method to set a URL to be used in all links.

class BaseSerializer
  include JSONAPI::Serializer

  def base_url
    'http://example.com'
  end
end

class PostSerializer < BaseSerializer
  attribute :title
  attribute :content

  has_one :author
  has_many :comments
end

JSONAPI::Serializer.serialize(post)

Returns:

{
  "data": {
    "id": "1",
    "type": "posts",
    "attributes": {
      "title": "Hello World",
      "content": "Your first post"
    },
    "links": {
      "self": "http://example.com/posts/1"
    },
    "relationships": {
      "author": {
        "links": {
          "self": "http://example.com/posts/1/relationships/author",
          "related": "http://example.com/posts/1/author"
        }
      },
      "comments": {
        "links": {
          "self": "http://example.com/posts/1/relationships/comments",
          "related": "http://example.com/posts/1/comments"
        },
      }
    }
  }
}

Alternatively, you can specify base_url as an argument to serialize which allows you to build the URL with different subdomains or other logic from the request:

JSONAPI::Serializer.serialize(post, base_url: 'http://example.com')

Note: if you override self_link in your serializer and leave out base_url, it will not be included.

Root metadata

You can pass a meta argument to specify top-level metadata:

JSONAPI::Serializer.serialize(post, meta: {copyright: 'Copyright 2015 Example Corp.'})

Root links

You can pass a links argument to specify top-level links:

JSONAPI::Serializer.serialize(post, links: {self: 'https://example.com/posts'})

Root errors

You can use serialize_errors method in order to specify top-level errors:

errors = [{ "title": "Invalid Attribute", "detail": "First name must contain at least three characters." }]
JSONAPI::Serializer.serialize_errors(errors)

If you are using Rails models (ActiveModel by default), you can pass in an object's errors:

JSONAPI::Serializer.serialize_errors(user.errors)

A more complete usage example (assumes ActiveModel):

class Api::V1::ReposController < Api::V1::BaseController
  def create
    post = Post.create(post_params)
    if post.errors
      render json: JSONAPI::Serializer.serialize_errors(post.errors)
    else
      render json: JSONAPI::Serializer.serialize(post)
    end
  end
end

Root 'jsonapi' object

You can pass a jsonapi argument to specify a top-level "jsonapi" key containing the version of JSON:API in use:

JSONAPI::Serializer.serialize(post, jsonapi: {version: '1.0'})

Namespace serializers

Assume you have an API with multiple versions:

module Api
  module V1
    class PostSerializer
      include JSONAPI::Serializer
      attribute :title
    end
  end
  module V2
    class PostSerializer
      include JSONAPI::Serializer
      attribute :name
    end
  end
end

With the namespace option you can choose which serializer is used.

JSONAPI::Serializer.serialize(post, namespace: Api::V1)
JSONAPI::Serializer.serialize(post, namespace: Api::V2)

Sparse fieldsets

The JSON:API spec allows to return only specific fields from attributes and relationships.

For example, if you wanted to return only the title field and author relationship link for posts:

fields =
JSONAPI::Serializer.serialize(post, fields: {posts: [:title]})

Sparse fieldsets also affect relationship links. In this case, only the author relationship link would be included:

JSONAPI::Serializer.serialize(post, fields: {posts: [:title, :author]})

Sparse fieldsets operate on a per-type basis, so they affect all resources in the response including in compound documents. For example, this will affect both the posts type in the primary data and the users type in the compound data:

JSONAPI::Serializer.serialize(
  post,
  fields: {posts: ['title', 'author'], users: ['name']},
  include: 'author',
)

Sparse fieldsets support comma-separated strings (fields: {posts: 'title,author'}, arrays of strings (fields: {posts: ['title', 'author']}), single symbols (fields: {posts: :title}), and arrays of symbols (fields: {posts: [:title, :author]}).

Relationships

You can easily specify relationships with the has_one and has_many directives.

class BaseSerializer
  include JSONAPI::Serializer
end

class PostSerializer < BaseSerializer
  attribute :title
  attribute :content

  has_one :author
  has_many :comments
end

class UserSerializer < BaseSerializer
  attribute :name
end

class CommentSerializer < BaseSerializer
  attribute :content

  has_one :user
end

Note that when serializing a post, the author association will come from the author attribute on the Post instance, no matter what type it is (in this case it is a User). This will work just fine, because JSONAPI::Serializers automatically finds serializer classes by appending Serializer to the object's class name. This behavior can be customized.

Because the full class name is used when discovering serializers, JSONAPI::Serializers works with any custom namespaces you might have, like a Rails Engine or standard Ruby module namespace.

Compound documents and includes

To reduce the number of HTTP requests, servers MAY allow responses that include related resources along with the requested primary resources. Such responses are called "compound documents". JSON:API Compound Documents

JSONAPI::Serializers supports compound documents with a simple include parameter.

For example:

JSONAPI::Serializer.serialize(post, include: ['author', 'comments', 'comments.user'])

Returns:

{
  "data": {
    "id": "1",
    "type": "posts",
    "attributes": {
      "title": "Hello World",
      "content": "Your first post"
    },
    "links": {
      "self": "/posts/1"
    },
    "relationships": {
      "author": {
        "links": {
          "self": "/posts/1/relationships/author",
          "related": "/posts/1/author"
        },
        "data": {
          "type": "users",
          "id": "1"
        }
      },
      "comments": {
        "links": {
          "self": "/posts/1/relationships/comments",
          "related": "/posts/1/comments"
        },
        "data": [
          {
            "type": "comments",
            "id": "1"
          }
        ]
      }
    }
  },
  "included": [
    {
      "id": "1",
      "type": "users",
      "attributes": {
        "name": "Post Author"
      },
      "links": {
        "self": "/users/1"
      }
    },
    {
      "id": "1",
      "type": "comments",
      "attributes": {
        "content": "Have no fear, sers, your king is safe."
      },
      "links": {
        "self": "/comments/1"
      },
      "relationships": {
        "user": {
          "links": {
            "self": "/comments/1/relationships/user",
            "related": "/comments/1/user"
          },
          "data": {
            "type": "users",
            "id": "2"
          }
        },
        "post": {
          "links": {
            "self": "/comments/1/relationships/post",
            "related": "/comments/1/post"
          }
        }
      }
    },
    {
      "id": "2",
      "type": "users",
      "attributes": {
        "name": "Barristan Selmy"
      },
      "links": {
        "self": "/users/2"
      }
    }
  ]
}

Notice a few things:

• The primary data relationships now include "linkage" information for each relationship that was included.

• The related objects themselves are loaded in the top-level included member.

• The related objects also include "linkage" data when a deeper relationship is also present in the compound document. This is a very powerful feature of the JSON:API spec, and allows you to deeply link complicated relationships all in the same document and in a single HTTP response. JSONAPI::Serializers automatically includes the correct linkage data for whatever include paths you specify. This conforms to this part of the spec:

  Note: Full linkage ensures that included resources are related to either the primary data (which could be resource objects or resource identifier objects) or to each other. JSON:API Compound Documents

Relationship path handling

The include param also accepts a string of relationship paths, ie. include: 'author,comments,comments.user' so you can pass an ?include query param directly through to the serialize method. Be aware that letting users pass arbitrary relationship paths might introduce security issues depending on your authorization setup, where a user could include a relationship they might not be authorized to see directly. Be aware of what you allow API users to include.

Control links and data in relationships

The JSON API spec allows relationships objects to contain links, data, or both.

By default, links are included in each relationship. You can remove links for a specific relationship by passing include_links: false to has_one or has_many. For example:

has_many :comments, include_links: false  # Default is include_links: true.

Notice that links are now excluded for the comments relationship:

   "relationships": {
     "author": {
       "links": {
         "self": "/posts/1/relationships/author",
         "related": "/posts/1/author"
       }
     },
     "comments": {}
   }

By default, data is excluded in each relationship. You can enable data for a specific relationship by passing include_data: true to has_one or has_many. For example:

has_one :author, include_data: true  # Default is include_data: false.

Notice that linkage data is now included for the author relationship:

   "relationships": {
     "author": {
       "links": {
         "self": "/posts/1/relationships/author",
         "related": "/posts/1/author"
       },
       "data": {
         "type": "users",
         "id": "1"
       }
     }

Rails example

# app/serializers/base_serializer.rb
class BaseSerializer
  include JSONAPI::Serializer

  def self_link
    "/api/v1#{super}"
  end
end

# app/serializers/post_serializer.rb
class PostSerializer < BaseSerializer
  attribute :title
  attribute :content
end

# app/controllers/api/v1/base_controller.rb
class Api::V1::BaseController < ActionController::Base
  # Convenience methods for serializing models:
  def serialize_model(model, options = {})
    options[:is_collection] = false
    JSONAPI::Serializer.serialize(model, options)
  end

  def serialize_models(models, options = {})
    options[:is_collection] = true
    JSONAPI::Serializer.serialize(models, options)
  end
end

# app/controllers/api/v1/posts_controller.rb
class Api::V1::ReposController < Api::V1::BaseController
  def index
    posts = Post.all
    render json: serialize_models(posts)
  end

  def show
    post = Post.find(params[:id])
    render json: serialize_model(post)
  end
end

# config/initializers/jsonapi_mimetypes.rb
# Without this mimetype registration, controllers will not automatically parse JSON API params.
module JSONAPI
  MIMETYPE = "application/vnd.api+json"
end
Mime::Type.register(JSONAPI::MIMETYPE, :api_json)

# Rails 4
ActionDispatch::ParamsParser::DEFAULT_PARSERS[Mime::Type.lookup(JSONAPI::MIMETYPE)] = lambda do |body|
  JSON.parse(body)
end

# Rails 5 moved DEFAULT_PARSERS
ActionDispatch::Http::Parameters::DEFAULT_PARSERS[:api_json] = lambda do |body|
  JSON.parse(body)
end
ActionDispatch::Request.parameter_parsers = ActionDispatch::Request::DEFAULT_PARSERS

Sinatra example

Here's an example using Sinatra and Sequel ORM instead of Rails and ActiveRecord. The important takeaways here are that:

1. The :tactical_eager_loading plugin will greatly reduce the number of queries performed when sideloading associated records. You can add this plugin to a single model (as demonstrated here), or globally to all models. For more information, please see the Sequel documentation.
2. The :skip_collection_check option must be set to true in order for JSONAPI::Serializer to be able to serialize a single Sequel::Model instance.
3. You should call #all on your Sequel::Dataset instances before passing them to JSONAPI::Serializer to greatly reduce the number of queries performed.

require 'sequel'
require 'sinatra/base'
require 'json'
require 'jsonapi-serializers'

class Post < Sequel::Model
  plugin :tactical_eager_loading

  one_to_many :comments
end

class Comment < Sequel::Model
  many_to_one :post
end

class BaseSerializer
  include JSONAPI::Serializer

  def self_link
    "/api/v1#{super}"
  end
end

class PostSerializer < BaseSerializer
  attributes :title, :content

  has_many :comments
end

class CommentSerializer < BaseSerializer
  attributes :username, :content

  has_one :post
end

module Api
  class V1 < Sinatra::Base
    configure do
      mime_type :api_json, 'application/vnd.api+json'

      set :database, Sequel.connect
    end

    helpers do
      def parse_request_body
        return unless request.body.respond_to?(:size) &&
          request.body.size > 0

        halt 415 unless request.content_type &&
          request.content_type[/^[^;]+/] == mime_type(:api_json)

        request.body.rewind
        JSON.parse(request.body.read, symbolize_names: true)
      end

      # Convenience methods for serializing models:
      def serialize_model(model, options = {})
        options[:is_collection] = false
        options[:skip_collection_check] = true
        JSONAPI::Serializer.serialize(model, options)
      end

      def serialize_models(models, options = {})
        options[:is_collection] = true
        JSONAPI::Serializer.serialize(models, options)
      end
    end

    before do
      halt 406 unless request.preferred_type.entry == mime_type(:api_json)
      @data = parse_request_body
      content_type :api_json
    end

    get '/posts' do
      posts = Post.all
      serialize_models(posts).to_json
    end

    get '/posts/:id' do
      post = Post[params[:id].to_i]
      not_found if post.nil?
      serialize_model(post, include: 'comments').to_json
    end
  end
end

See also: Sinja, which extends Sinatra and leverages jsonapi-serializers to provide a JSON:API framework.

Changelog

See Releases.

Unfinished business

• Support for pagination/sorting is unlikely to be supported because it would likely involve coupling to ActiveRecord, but please open an issue if you have ideas of how to support this generically.

Contributing

1. Fork it ( https://github.com/fotinakis/jsonapi-serializers/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Throw a ★ on it! :)