README.md

Demonstration of surprising association order dependency in activerecord

See it be weird:

$ bundle install
$ bundle exec ruby boom.rb

boom.rb

require "./foo"

f = Foo.create!
Bar.create!(foo_ids: [f.id])

foo.rb

require "active_record"
require "logger"

ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'
ActiveRecord::Base.connection.create_table :foos do |t|
end
ActiveRecord::Base.connection.create_table :bars do |t|
end
ActiveRecord::Base.connection.create_table :foo_bars do |t|
  t.belongs_to :foo, null: false
  t.belongs_to :bar, null: false
end

class Foo < ActiveRecord::Base
  has_many :bars, through: :foo_bars
  has_many :foo_bars
end
class Bar < ActiveRecord::Base
  has_many :foos, through: :foo_bars
  has_many :foo_bars
end
class FooBar < ActiveRecord::Base
  belongs_to :foo
  belongs_to :bar
end

Gemfile

source "https://rubygems.org"
gem "activerecord"#, "4.2.7.1"
gem "sqlite3"

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    activemodel (5.0.1)
      activesupport (= 5.0.1)
    activerecord (5.0.1)
      activemodel (= 5.0.1)
      activesupport (= 5.0.1)
      arel (~> 7.0)
    activesupport (5.0.1)
      concurrent-ruby (~> 1.0, >= 1.0.2)
      i18n (~> 0.7)
      minitest (~> 5.1)
      tzinfo (~> 1.1)
    arel (7.1.4)
    concurrent-ruby (1.0.4)
    i18n (0.8.0)
    minitest (5.10.1)
    sqlite3 (1.3.13)
    thread_safe (0.3.5)
    tzinfo (1.2.2)
      thread_safe (~> 0.1)

PLATFORMS
  ruby

DEPENDENCIES
  activerecord
  sqlite3

BUNDLED WITH
   1.13.7