Build a small Rails API with Serializers

I. Description

1. Rails version: 5.2.3
2. Ruby version: 2.5.3
3. Database: Postgres
4. Describe:

• The goal of the API is to sends Photos back with the Comments associated.
• The API has 2 models:
  • Photo: The attributes will be the title and photo_url_string .
  • Comment: The attributes will be content and owner and photo_id .
• The association is a photo having many comments while a comment belongs to a photo.

II. Setup

1. To generate the API using the command:

rails _5.2.3_ new photo_api --database=postgresql --api

• The flag --database=postgresql to indicate Postgres is used to save the data.
• The flag --api to avoid generating the views and view helpers since they are not necessary for an API.

2. Install gem rack-cors

• Navigate to the folder of the project.
• Edit the Gemfile :

gem 'rack-cors'

• Why we need to install this gem?

What is CORS? CORS is Cross Origin Resource Sharing This gem allows CORS in the API. CORS prevents API calls from unknow origins.

3. Install gem active_model_serializers

gem 'active_model_serializers'

• Why we need to install this gem?

The serializer gem is used to structure the format of the data when requests are made.

4. Config CORS

• Navigate to config/inintializers/cors.rb and uncomment the following code:

Rails.application.config.middleware.insert_before 0, Rack:Cors do
  allow do
    origins '*'

    resource '*',
    headers: :any,
    methods: %i(get post put patch delete options head)
  end
end

Explain this code: Within the allow block, origins '*' is allowing from all origins as well as allowing GET, POST, PUT, PATCH, and DELETE requests to the API.

III. Config database and create databsse

IV. Setup models and controllers

1. Generate model Photo and Comment

rails g model Photo title photo_url_string
rails g model Comment content:text owner photo_id:integer

2. Define association between photo model and comment model

class Photo < ApplicationRecord
  has_many :comments
  validates_presence_of :title
end

class Comment < ApplicationRecord
  belongs_to :photo
end

3. Generate controllers Photos and Comments

rails g controller api/v1/Photos
rails g controller api/v1/Comments

Since this is the first version of the API, the controllers should be inside api/v1 .

4. Update the controllers

class Api::V1::PhotosController < ApplicationController
  before_action :get_photo, only: %i(show update)
  def index
    @photos = Photo.all
    render json: @photos
  end
  def show
    render json: @photo
  end
  def update
    @photo.update(photo_params)
    if @photo.valid?
      render json: @photo
    else
      render json: { errors: @photo.errors.full_messages }
    end
  end
  private
    def photo_params
      params.require(:photo).permit(:title, :photo_url_string)
    end
    def get_photo
      @photo = Photo.find(params[:photo_id])
    end
end

Explain this code:

1. All photos are rendered in the form of JSON
2. The photo_params represent the data received from the front-end
3. The photo_params method is permitting the keys title and photo_url_string whenever a PATCH request is made.

class Api::V1::CommentsController < ApplicationController
  def create
    @comment = Comment.new(comment_params)
    if @comment.valid?
      render json: @comment
    else
      render json: { errors: @comment.errors.full_messages }
    end
  end
  private
    def comment_params
      params.require(:comment).permit(:content, :owner, :photo_id)
    end
end

5. Update the routes

Rails.application.routes.draw do
  namespace :api do
    namespace :v1 do
      resources :photos, only: %i(index show update) do
        resources :comments, only: :create
      end
    end
  end
end

6. Seed data

• Navigate to db/seed.rb and input some seed data:

photo1 = Photo.create(title: 'Heart', photo_url_string: 'https://images.unsplash.com/photo-1581022414232-7c2eb612b50f?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80')
photo2 = Photo.create(title: 'Baby', photo_url_string: 'https://images.unsplash.com/photo-1581095863507-f121a8693129?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80')
comment1 = Comment.create(content: 'Awesome picture', owner: 'Unsplash 1', photo_id: photo1.id)
comment2 = Comment.create(content: 'Hmm, this is romantic picture', owner: 'Unsplash 2', photo_id: photo1.id)
comment3 = Comment.create(content: 'Haha picture', owner: 'Unsplash 3', photo_id: photo2.id)
comment4 = Comment.create(content: 'Not bad', owner: 'Unsplash 4', photo_id: photo2.id)

• Run command to create the data:

rails db:seed

7. Serialize attributes which JSON response

• Run command:

rails g serializer photo

• Navigate to serializers/photo_serializer.rb :

class PhotoSerializer < ActiveModel::Serializer
  attributes :title, :photo_url_string
end

• At this point, only title and photo_url_string are sent in the JSON response. With serializers, the response can be structured to include certain information. The problem with the missing comments still persists. The comments must be included. Let's update the photo serializer.

class PhotoSerializer < ActiveModel::Serializer
  has_many :comments
  attributes :title, :photo_url_string
end

• Serializer comment:

rails g serializer comment

class CommentSerializer < ActiveModel::Serializer
  attributes :content, :owner
end

V. Working with Postman

1. Get request
2. POST/PATCH request
3. Delete request

VI. Notes

1. How to create variables environment?

• In the application, I use a file local_env.yml to store username and password for config DB.
• Reference link: (https://itnext.io/environment-variables-in-ruby-on-rails-17e4934cfd71)
• In the database.yml : Use <%= %> to Ruby can read the value.

<%= ENV["USERNAME"] %>