Invalid Includes

gistfile1.rb

# require 'bundler'
# Bundler.require

require 'active_record'
require 'rails'
require 'minitest/autorun'
require 'logger'

db_name = 'rails-check'

ActiveRecord::Base.establish_connection adapter: 'mysql2', database: 'mysql', host: 'localhost'
ActiveRecord::Base.connection.drop_database db_name rescue nil
ActiveRecord::Base.connection.create_database db_name
ActiveRecord::Base.connection.close
ActiveRecord::Base.establish_connection adapter: 'mysql2', database: db_name, host: 'localhost'

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

ActiveRecord::Schema.define do
  create_table 'products', force: true do |t|
    t.string  'name'            # 商品名
    t.integer 'corporation_id'  # 商品製造会社
    t.integer 'shop_id'         # 商品取扱店
  end
  create_table "shops", force: true do |t|
    t.string 'name'             # 店名
    t.string 'corporation_id'   # 本社
  end
  create_table "corporations", force: true do |t|
    t.string "name"             # 社名
  end
end

class Product < ActiveRecord::Base
  belongs_to :corporation
  belongs_to :shop
end

class Shop < ActiveRecord::Base
  has_one :product
  belongs_to :corporation
end

class Corporation < ActiveRecord::Base
  has_many :products
  has_many :shops
end

class CheckEagerLoad < MiniTest::Unit::TestCase
  def setup
    Corporation.new(id: 1, name: 'DummyCompany').save
    Corporation.new(id: 2, name: 'AShopHead').save
    Shop.new(id: 1, name: 'AShop', corporation_id: 2).save
    Product.new(id: 1, name: 'Product', corporation_id: 1, shop_id: 1).save
  end

  def teardown
    Corporation.delete_all
    Shop.delete_all
    Product.delete_all
  end

  def test_no_eager_load
    product = Product.joins(:corporation).joins(shop: :corporation).first
    assert_equal 1, product.corporation.id
    assert_equal 1, product.corporation_id
  end

  def test_eager_load_success_test
    product = Product.includes(:corporation).references(:corporation).joins(:corporation).joins(shop: :corporation).first
    assert_equal 1, product.corporation.id
    assert_equal 1, product.corporation_id
  end

  # joinの順番を変えると失敗する
  # eager loadが勘違い、どちらのcorporationをProductに結びつけていいか判断がつかないから?
  def test_eager_load_fail_test
    product = Product.includes(:corporation).references(:corporation).joins(shop: :corporation).joins(:corporation).first
    # product.corporation.id と product.corporation_id が異なる結果となる
    assert_equal 1, product.corporation.id
    assert_equal 1, product.corporation_id
  end
end