json-serializer

Customizes JSON output through serializer objects.

A minimal implementation of active_model_serializers gem.

Installation

gem install json-serializer

Usage

Basics

Here's a simple example:

require "json_serializer"

class UserSerializer < JsonSerializer
  attribute :id
  attribute :first_name
  attribute :last_name
end

In this case, we defined a new serializer class and specified the attributes we would like to include in the serialized form.

user = User.create(first_name: "Sonny", last_name: "Moore", admin: true)

UserSerializer.new(user).to_json
# => "{\"id\":1,\"first_name\":\"Sonny\",\"last_name\":\"Moore\"}"

You can add a root to the outputted json through the :root option:

user = User.create(first_name: "Sonny", last_name: "Moore", admin: true)

UserSerializer.new(user).to_json(root: :user)
# => "{\"user\":{\"id\":1,\"first_name\":\"Sonny\",\"last_name\":\"Moore\"}}"

Arrays

A serializer can be used for objects contained in an array:

require "json_serializer"

class PostSerializer < JsonSerializer
  attribute :id
  attribute :title
  attribute :body
end

posts = []
posts << Post.create(title: "Post 1", body: "Hello!")
posts << Post.create(title: "Post 2", body: "Goodbye!")

PostSerializer.new(posts).to_json

Given the example above, it will return a json output like:

[
  { "id": 1, "title": "Post 1", "body": "Hello!" },
  { "id": 2, "title": "Post 2", "body": "Goodbye!" }
]

Attributes

By default, before looking up the attribute on the object, it checks the presence of a method with the name of the attribute. This allow serializes to include properties in addition to the object attributes or customize the result of a specified attribute. You can access the object being serialized with the +object+ method.

require "json_serializer"

class UserSerializer < JsonSerializer
  attribute :id
  attribute :first_name
  attribute :last_name
  attribute :full_name

  def full_name
    object.first_name + " " + object.last_name
  end
end

user = User.create(first_name: "Sonny", last_name: "Moore")

UserSerializer.new(user).to_json
# => "{\"id\":1,\"first_name\":\"Sonny\",\"last_name\":\"Moore\",\"full_name\":\"Sonny Moore\"}"

If you would like direct, low-level control of attribute serialization, you can completely override to_hash method to return the hash you need:

require "json_serializer"

class UserSerializer < JsonSerializer
  attribute :id
  attribute :first_name
  attribute :last_name

  attr :current_user

  def initialize(object, current_user)
    super(object)
    @current_user = current_user
  end

  def to_hash
    hash = super
    hash.merge!(admin: object.admin) if current_user.admin?
    hash
  end
end

Attributes with Custom Serializer

You can specify a serializer class for a defined attribute. This is very useful for serializing each element of an association.

require "json_serializer"

class UserSerializer < JsonSerializer
  attribute :id
  attribute :username
end

class PostSerializer < JsonSerializer
  attribute :id
  attribute :title
  attribute :user, :UserSerializer
  attribute :comments, :CommentSerializer
end

class CommentSerializer < JsonSerializer
  attribute :id
  attribute :content
  attribute :user, :UserSerializer
end

admin = User.create(username: "admin", admin: true)
user  = User.create(username: "user")

post = Post.create(title: "Hello!", user: admin)
post.comments << Comment.create(content: "First comment", user: user)

PostSerializer.new(post).to_json

The example above returns the following json output:

{
  "id": 1,
  "title": "Hello!",
  "user":
    {
      "id": 1,
      "username": "admin"
    },
  "comments":
    [
      {
        "id": 1,
        "content": "First comment",
        "user":
          {
            "id": 2,
            "username": "user"
          }
      }
    ]
}

bemurphy / json-serializer