polymorphic_join_bug.rb

unless File.exist?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    gem 'rails', github: 'rails/rails'
    gem 'arel', github: 'rails/arel'
    gem 'sqlite3'
  GEMFILE

  system 'bundle install'
end

require 'bundler'
Bundler.setup(:default)

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

# 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 :centers do |t|
  end

  create_table :lefts do |t|
  end

  create_table :rights do |t|
  end

  create_table :links do |t|
    t.integer  :center_id
    t.integer  :linkable_id
    t.string   :linkable_type
  end
end

class Center < ActiveRecord::Base
  has_many :links

  has_many :left_links, -> { where(linkable_type: "Left") }, class_name: "Link"
  has_many :lefts, through: :left_links, source: :linkable, source_type: "Left"

  has_many :right_links, -> { where(linkable_type: "Right") }, class_name: "Link"
  has_many :rights, through: :right_links, source: :linkable, source_type: "Right"

  scope :with_right, -> (right) {
    joins(:rights).where(rights: {id: right.id})
  }

  scope :with_left, -> (left) {
    joins(:lefts).where(lefts: {id: left.id})
  }

  scope :with_left_and_right, -> (left, right) {
    joins(:lefts).joins(:rights).where(lefts: {id: left.id}, rights: {id: right.id})
  }
end

class Left < ActiveRecord::Base
  has_many :links, -> { where(linkable_type: "Left") }, as: :linkable
  has_many :centers, through: :links
end

class Right < ActiveRecord::Base
  has_many :links, -> { where(linkable_type: "Right") }, as: :linkable
  has_many :centers, through: :links
end

class Link < ActiveRecord::Base
  belongs_to :center
  belongs_to :linkable, polymorphic: true
end

class BugTest < Minitest::Test
  def test_polymorphic_join
    center = Center.create
    left = Left.create
    right = Right.create
    center.lefts << left
    center.rights << right

    assert_equal 1, center.rights.count
    assert_equal 1, center.lefts.count
    assert_equal 1, left.centers.with_right(right).count #Fails
  end
end