Creating Custom Attributes for Serialization

In my latest project, I created a Single Page JavaScript Application utilizing a Rails API backend. On the backend, the action must convert the data to JSON when passing information to be rendered. The following example uses the Fast JSON API serializer for Ruby Objects.

When using the Fast JSON API serializer, we must specify the attributes to be included. Let’s use the two models below as an example.

class User < ApplicationRecord
    attr_accessor :username
    has_many :games
end

class Game < ApplicationRecord
    attr_accessor :score, :user_id
    belongs_to :user
end

In each model’s serializer, simply add the attribute names to the attributes method to make them available to the view. Here, I’m including the username attribute from my user model.

class UserSerializer
  include FastJsonapi::ObjectSerializer

  attributes :username
end

However, I’d also like to render more information about each user instance. For example, I want to show each user’s high score, but that is not an attribute on my user model. This is where custom attributes come in handy. To create a custom attribute with Fast JSON API, we can do so using Ruby block syntax in the serializer class.

class UserSerializer
  include FastJsonapi::ObjectSerializer

  attributes :username

  attributes :high_score do |object|
    object.games.map(&:score).max
  end
end

To get a user’s high score, I first need all the game instances that belong to the user. After getting all the user’s games, I want to put the game scores in a collection and find the highest value, using max.

By using the above block syntax, that is set to a custom attribute name, I can get the user’s high score in my serialized data for rendering. Now, here’s what the output JSON looks like:

{
  "data": {
    "id": "1",
    "type": "user",
    "attributes": {
      "username": "natalie",
      "high_score": "7"
    },
    ...
}

There are also ways to override an object’s property or an attribute’s name when using Fast JSON API. More information on this can be found in the documentation.

I hope this has helped or inspired you to create a custom attribute for serialization!