Thoughtbot upcase: Querying belongs_to Associations

belongs_to.rb

# frozen_string_literal: true

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  git_source(:github) { |repo| "https://github.com/#{repo}.git" }
  gem "rails", "5.2.0"
  gem "sqlite3"
end

require "active_record"
require "logger"
require 'rails'


ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :roles, force: true do |t|
    t.string :position
    t.boolean :billable
  end

  create_table :people, force: true do |t|
    t.string :name
    t.integer :role_id
  end
end

class Person < ActiveRecord::Base
  belongs_to :role
end

class Role < ActiveRecord::Base
  has_many :people
end

role1 = Role.create(position: 'Developer Junior', billable: true)
role2 = Role.create(position: 'Developer Senior', billable: false)

person1 = Person.create(name: 'wait', role_id: role1.id)
person2 = Person.create(name: 'but', role_id: role1.id)
person3 = Person.create(name: 'why', role_id: role2.id)

puts "Person 1 is named: #{person1.name} and has role #{person1.role_id}"
puts "Person 2 is named: #{person2.name} and has role #{person2.role_id}"
puts "Person 3 is named: #{person3.name} and has role #{person3.role_id}"

puts ''
puts "----------------Performing Person.all"
puts Person.all

puts ''
puts "----------------Performing Person.all.select { |person| person.role.billable? }"
puts Person.all.select { |person| person.role.billable? }

puts ''
puts '----------------A better way would be to glue tables together so ActiveRecord performs a SQL join on its associations'
puts "----------------Performing Person.all.joins(:role)"
puts Person.all.joins(:role)

puts ''
puts '----------------We could now filter by billable or not'
puts "----------------Performing Person.all.joins(:role).where(roles: { billable: true })"
puts Person.all.joins(:role).where(roles: { billable: true })

puts ''
puts '----------------Now we can define a class method in Role to filter on billable'

class Role < ActiveRecord::Base
  def self.billable
    where(billable: true)
  end
end

puts "----------------Performing Person.joins(:role).merge(Role.billable)"
puts Person.joins(:role).merge(Role.billable)

class Person < ActiveRecord::Base
  def self.billable
    joins(:role).merge(Role.billable)
  end
end

puts ''
puts '----------------The best option is to create a class method in Person and call billable directly on Person'
puts "----------------Performing Person.billable"
puts Person.billable