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ActiveModel::Serializers brings convention over configuration to your JSON generation.

AMS does this through two components: serializers and adapters. Serializers describe which attributes and relationships should be serialized. Adapters describe how attributes and relationships should be serialized.


This is the master branch of AMS. It will become the 0.10.0 release when it's ready, but it's not. You probably don't want to use it yet. As such, we recommend that any new projects you start use the latest 0.8.x version of this gem. This version is the most widely used, and will most closely resemble the forthcoming release.

There are two released versions of AMS that you may want to use: 0.9.x and 0.8.x. 9 was recently master, so if you were using master, you probably want to use it. 8 was the version that was on RubyGems, so if you were using that, that's probably what you want.

0.10.x will be based on the 0.8.0 code, but with a more flexible architecture. We'd love your help.

For more, please see the rails-api-core mailing list.



Given two models, a Post(title: string, body: text) and a Comment(name:string, body:text, post_id:integer), you will have two serializers:

class PostSerializer < ActiveModel::Serializer
  attributes :title, :body

  has_many :comments

  url :post


class CommentSerializer < ActiveModel::Serializer
  attributes :name, :body

  belongs_to :post

  url [:post, :comment]

Generally speaking, you as a user of AMS will write (or generate) these serializer classes. If you want to use a different adapter, such as a JsonApi, you can change this in an initializer:

ActiveModel::Serializer.config.adapter = ActiveModel::Serializer::Adapter::JsonApi


ActiveModel::Serializer.config.adapter = :json_api

You won't need to implement an adapter unless you wish to use a new format or media type with AMS.

If you would like the key in the outputted JSON to be different from its name in ActiveRecord, you can use the :key option to customize it:

class PostSerializer < ActiveModel::Serializer
  attributes :id, :body

  # look up :subject on the model, but use +title+ in the JSON
  attribute :subject, :key => :title
  has_many :comments

In your controllers, when you use render :json, Rails will now first search for a serializer for the object and use it if available.

class PostsController < ApplicationController
  def show
    @post = Post.find(params[:id])

    render json: @post

In this case, Rails will look for a serializer named PostSerializer, and if it exists, use it to serialize the Post.

Specify a serializer

If you wish to use a serializer other than the default, you can explicitly pass it to the renderer.

1. For a resource:

  render json: @post, serializer: PostPreviewSerializer

2. For an array resource:

# Use the default `ArraySerializer`, which will use `each_serializer` to
# serialize each element
render json: @posts, each_serializer: PostPreviewSerializer

# Or, you can explicitly provide the collection serializer as well
render json: @posts, serializer: PaginatedSerializer, each_serializer: PostPreviewSerializer


If you want a meta attribute in your response, specify it in the render call:

render json: @post, meta: { total: 10 }

The key can be customized using meta_key option.

render json: @post, meta: { total: 10 }, meta_key: "custom_meta"

meta will only be included in your response if there's a root. For instance, it won't be included in array responses.

Root key

If you want to define a custom root for your response, specify it in the render call:

render json: @post, root: "articles"

Built in Adapters


This adapter follows the format specified in It will include the associated resources in the "linked" member when the resource names are included in the include option.

  render @posts, include: 'authors,comments'


Add this line to your application's Gemfile:

gem 'active_model_serializers'

And then execute:

$ bundle

Creating a Serializer

The easiest way to create a new serializer is to generate a new resource, which will generate a serializer at the same time:

$ rails g resource post title:string body:string

This will generate a serializer in app/serializers/post_serializer.rb for your new model. You can also generate a serializer for an existing model with the serializer generator:

$ rails g serializer post

The generated seralizer will contain basic attributes and has_many/belongs_to declarations, based on the model. For example:

class PostSerializer < ActiveModel::Serializer
  attributes :title, :body

  has_many :comments

  url :post


class CommentSerializer < ActiveModel::Serializer
  attributes :name, :body

  belongs_to :post_id

  url [:post, :comment]

The attribute names are a whitelist of attributes to be serialized.

The has_many and belongs_to declarations describe relationships between resources. By default, when you serialize a Post, you will get its Comments as well.

You may also use the :serializer option to specify a custom serializer class, for example:

  has_many :comments, serializer: CommentPreviewSerializer

The url declaration describes which named routes to use while generating URLs for your JSON. Not every adapter will require URLs.

Getting Help

If you find a bug, please report an Issue.

If you have a question, please post to Stack Overflow.



  1. Fork it ( )
  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