gistfile1.rb

gem 'activerecord', '4.1.5'

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

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

ActiveRecord::Schema.define do
  create_table :users do |t|
    t.integer :saved_count
    t.timestamps
  end

  create_table :profiles do |t|
    t.integer :user_id
    t.integer :post_id
    t.timestamps
  end

  create_table :posts do |t|
    t.string :content
    t.timestamps
  end
end

class User < ActiveRecord::Base
  has_many :profiles
  has_many :posts, through: :profiles
  before_save -> { increment :saved_count }
end

class Profile < ActiveRecord::Base
  belongs_to :user
  belongs_to :post
end

class Post < ActiveRecord::Base
  has_one :profile
  has_one :user, through: :profile
end

class BugTest < MiniTest::Unit::TestCase
  def test_saving_post_does_not_save_user_when_relation_is_not_referenced
    user = User.create!
    post = Post.create!(content: 'foo')
    profile = Profile.create!(post: post, user: user)
    post.save
    assert_equal 1, user.reload.saved_count
    # if we do not reference post.user, then the user is not touched (correct)
    post.save
    assert_equal 1, user.reload.saved_count
  end
  
  def test_saving_post_does_not_save_user_when_relation_is_referenced
    user = User.create!
    post = Post.create!(content: 'foo')
    profile = Profile.create!(post: post, user: user)
    post.save
    assert_equal 1, user.reload.saved_count
    post.user # necessary to create the reference
    # but now post.save will also save user even though there are no changes
    post.save
    assert_equal 1, user.reload.saved_count
  end
end