Given 3 models: User, Book, Reading. How to return a list of all books and mark the ones read by a given user.
The result could look something like:
[
{
"id": 1,
"title": "To Kill a Mockingbird",
"read": false
},
{
"id": 2,
"title": "East of Eden",
"read": true
},
{
"id": 3,
"title": "On the Road",
"read": false
}
]Where read indicates there is a Reading object linking this Book to this User
| class Book < ApplicationRecord | |
| has_many :readings, dependent: :destroy | |
| validates :title, presence: true | |
| end |
| class BookSerializer < ActiveModel::Serializer | |
| attributes :id, :title, :read | |
| def read | |
| object.read | |
| end | |
| end |
| SELECT books.*, CASE WHEN readings.id IS NULL THEN false ELSE true END as read | |
| FROM "books" | |
| LEFT OUTER JOIN "readings" ON "readings"."book_id" = "books"."id" and user_id = '<some id>'; |
| class Reading < ApplicationRecord | |
| belongs_to :user | |
| belongs_to :book | |
| end |
| class User < ApplicationRecord | |
| has_many :readings, dependent: :destroy | |
| validates :name, present: true | |
| end |
| class UsersController < ApplicationController | |
| def reading_list | |
| books = Book | |
| .select('books.*, CASE WHEN readings.id IS NULL THEN false ELSE true END as read') | |
| .joins("LEFT OUTER JOIN readings ON reagins.book_id = books.id AND readings.user_id = '#{current_user.id}'") | |
| .all | |
| render json: books | |
| end | |
| end |