issue 18061

test_ar.rb

# rails/rails#18061
# env vars: AR_VERSION (see below for default), TRY_PATCH (default false)
system 'rm Gemfile' if File.exist?('Gemfile')

$ar_version = ENV['AR_VERSION']
# $ar_version ||= '5.0.0.beta3'   # succeeds, patch does not apply (lacks #where_values)
$ar_version ||= '4.2.6'         # fails, patch works
# $ar_version ||= '4.1.15'        # fails, patch works
# $ar_version ||= '4.0.13'        # fails, patch works

$try_patch = ENV['TRY_PATCH'] == 'true'
$enable_byebug = false

File.write('Gemfile', <<-GEMFILE)
  source 'https://rubygems.org'
  gem 'activerecord',
    #{$ar_version.inspect}
  gem 'sqlite3'
  #{"gem 'byebug'" if $enable_byebug}
GEMFILE

system 'bundle install'

require 'byebug' if $enable_byebug
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 :businesses do |t|
    t.string :type
    t.integer :registry_id
  end

  create_table :memberships do |t|
    t.integer :company_id
    t.integer :foundation_id

    t.date :expires_at
  end

  create_table :registries do |t|
  end
end

class Registry < ActiveRecord::Base
  has_many :foundations
  has_many :companies,
    through: :foundations

  module TargetScopeFix
    def association(*args)
      (args[0] == :companies) ? super.extend(Association) : super
    end

    module Association
      def target_scope
        super.tap { |scope| 
          scope.where_values.delete_if { |node|
            left = node.left
            right = node.right[0]
            Arel::Nodes::In === node && 
              left.relation.name == 'businesses' &&
              left.name.to_s == 'type' &&
              # #val is for 4.2
              (right.respond_to?(:val) ? right.val : right) != 'Company'
          }
        }
      end
    end
  end

  include TargetScopeFix if $try_patch
end

class Business < ActiveRecord::Base
end

class Foundation < Business
  belongs_to :registry

  has_many :memberships
  has_many :companies,
    through: :memberships
end

class Company < Business
  has_many :memberships
  has_many :foundations,
    through: :memberships
end

class Membership < ActiveRecord::Base
  belongs_to :foundation
  belongs_to :company
end

# class BugTest < Minitest::Test
class BugTest < MiniTest::Unit::TestCase
  def setup
    companya = Company.create
    companyb = Company.create
    foundationa = Foundation.create
    foundationb = Foundation.create

    registry = Registry.create
    registryb = Registry.create

    companya.memberships.create foundation: foundationa
    companya.memberships.create foundation: foundationb
    companyb.memberships.create foundation: foundationb
    registry.foundations << foundationa

    registryb.foundations << foundationb
  end

  # generated query:
  # SELECT "businesses".*
  #   FROM "businesses"
  #     INNER JOIN "memberships"
  #       ON "businesses"."id" = "memberships"."company_id"
  #     INNER JOIN "businesses" "foundations_companies_join"
  #       ON "memberships"."foundation_id" = "foundations_companies_join"."id"
  #   WHERE "businesses"."type" IN ('Foundation') <<< foundations_companies_join! <<<<<<<<<<<<<<<<<
  #     AND "businesses"."type" IN ('Company')
  #     AND "foundations_companies_join"."registry_id" = ?
  def test_has_many_through_through_with_sti_aliasing
    reg = Registry.first
    regb = Registry.last

    assert_equal 1, reg.companies.count
    assert_equal 2, regb.companies.count
  end
end

relevant for rails/rails#18061 and rails/rails#18062

uploaded newer version with ugly workaround

split stuff about #18062 => https://gist.github.com/nachokb/b12c26af8fa4740d1230