rails_touch_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.
  gem "activerecord", "5.1.0"
  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::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.timestamps
  end

  create_table :tags, force: true

  create_table :taggings, force: true do |t|
    t.references :post
    t.references :tag
  end
end

class Post < ActiveRecord::Base
  has_many :taggings
  has_many :tags, through: :taggings
end

class Tagging < ActiveRecord::Base
  belongs_to :post, touch: true
  belongs_to :tag
end

class Tag < ActiveRecord::Base
end

class BugTest < Minitest::Test
  def test_has_many_through_touch
    post = Post.create!
    tag = Tag.create!

    updated_at_before_tag_added = post.updated_at
    post.update(tags: [tag])
    updated_at_after_tag_added = post.updated_at

    assert_equal 1, post.tags.count
    assert updated_at_before_tag_added < updated_at_after_tag_added

    updated_at_before_tag_removed = post.updated_at
    post.update(tags: [])
    updated_at_after_tag_removed = post.updated_at

    assert_equal 0, post.tags.count
    assert updated_at_before_tag_removed < updated_at_after_tag_removed, "post is not touched"
  end
end