rails issue 19087

gistfile1.txt

# Activate the gem you are reporting the issue against.
gem 'activerecord', '4.2.1.rc2'
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|
  end

  create_table :comments, force: true do |t|
    t.integer :commentable_id
    t.string :commentable_type
  end
end

module CommentSource
  extend ActiveSupport::Concern

  included do
    has_many :comments, as: :commentable
  end
end

class Post < ActiveRecord::Base
  include CommentSource
end

class Comment < ActiveRecord::Base
  belongs_to :post, polymorphic: true
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = Post.create!
    post.comments << Comment.create!

    assert_equal 1, post.comments.count
    assert_equal 1, Comment.count

    assert_equal [], Comment.where(commentable: []).to_a
    assert_equal [], Post.where(comments: []).to_a
  end
end