Rails 4.2.7 - STI + HasManyThrough - Incorrect query being generated

ar_4_2_bug.rb

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"
  # Activate the gem you are reporting the issue against.
  if ENV['AR'] == '5'
    gem "activerecord", '5.0.0'
  else
    gem "activerecord", '4.2.7'
  end

  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")

ActiveRecord::Schema.define do
  create_table :destinations, force: true do |t|
    t.integer :parent_id
    t.string :type
    t.string :name
  end

  create_table :attractions, force: true do |t|
    t.string :name
  end

  create_join_table :attractions, :destinations, force: true do |t|
    t.index :attraction_id
    t.index :destination_id
  end
end

class Destination < ActiveRecord::Base
end

class Continent < Destination
  has_many :countries, foreign_key: :parent_id
  has_many :states, through: :countries
  has_many :cities, through: :states
end

class Country < Destination
  belongs_to :continent, foreign_key: :parent_id
  has_many :states, foreign_key: :parent_id
  has_many :cities, through: :states
end

class State < Destination
  belongs_to :country, foreign_key: :parent_id
  has_many :cities, foreign_key: :parent_id
  has_one :continent, through: :country
end

class City < Destination
  belongs_to :state, foreign_key: :parent_id
  has_one :country, through: :state
  has_one :continent, through: :state
end

class BugTest < Minitest::Test
  def test_ar_4_2_creates_incorrect_sql
    south_america   = Continent.where(name: 'South America').first_or_create!
    brazil          = Country.where(name: 'Brazil', parent_id: south_america.id).first_or_create!
    sao_paulo_state = State.where(name: 'São Paulo', parent_id: brazil.id).first_or_create!
    sao_paulo_city  = City.where(name: 'São Paulo', parent_id: sao_paulo_state).first_or_create!

    ActiveRecord::Base.logger = Logger.new(STDOUT)

    assert_equal 1, south_america.city_ids.count
  end
end