The problem

Recently, I have attempted to completely switch to JsonAPI specification for all my API-only rails projects. To achieve these with ease, I use Jsonapi resources gem. This gem is very handy to use and get’s you configured for JsonAPI specs in no time. But sometimes, its not clear how to do what you would normally do if you are not using the tool. One of those issues is adding custom fields to the json objects from the ActiveRecords being serialized. I will show you my solution to the this challenge.

Solution

Given a user model:

# Table name: `users`
#
# ### Columns

# Name                          | Type               | Attributes
# ----------------------------- | ------------------ | ---------------------------
# **`id`**                      | `uuid`             | `not null, primary key`
# **`first_name`**              | `string`           |
# **`last_name`**               | `string`           |
...
class User < ActiveRecord::Base      
  def fullname
    self.first_name + " " +  self.last_name
  end
end

We are interested in showing a full_name as part of the returned json user object. We can add the following snippet to user_resource.rb file

# File: app/api/v1/resources/user_resource.rb
class Api::V1::UserResource < Api::V1::ApiResource
    begin
        attributes *User.attribute_names.map(&:to_sym) - %i[id]  + %i[full_name]   
    rescue
    end 
end

This way, we are sure of getting the full_name key as part of the returned json object.