polymorphic_query_test.rb

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.1.0"
  gem "sqlite3"
end

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 :comments, force: true do |t|
    t.string :comment
    t.string :ref_id
    t.string :ref_type
  end

  create_table :books, force: true do |t|
    t.string :title
  end

  create_table :articles, force: true do |t|
    t.string :title
  end
end

class Comment < ActiveRecord::Base
  belongs_to :book,    class_name: 'Book',    foreign_key: 'ref_id'
  belongs_to :article, class_name: 'Article', foreign_key: 'ref_id'
  belongs_to :ref,     polymorphic: true

  def self.distinct_titles
    comment_ids = ids
    Article.titles_for_comments(comment_ids) + Book.titles_for_comments(comment_ids)
  end
end

class Book < ActiveRecord::Base
  has_many :comments, as: :ref

  def self.titles_for_comments(comment_ids)
    joins(:comments).where(comments: { id: comment_ids }).distinct.pluck(:title)
  end
end

class Article < ActiveRecord::Base
  has_many :comments, as: :ref

  def self.titles_for_comments(comment_ids)
    joins(:comments).where(comments: { id: comment_ids }).distinct.pluck(:title)
  end
end

class BugTest < Minitest::Test
  def test_association_stuff
    book_one   = Book.create! title: 'Book1'
    book_two   = Book.create! title: 'Book2'
    book_three = Book.create! title: 'Book3'

    article_one = Article.create! title: 'Article1'
    article_two = Article.create! title: 'Article2'

    book_one.comments    << Comment.create!(comment: 'comment1')
    book_one.comments    << Comment.create!(comment: 'comment2')
    article_one.comments << Comment.create!(comment: 'comment3')
    book_three.comments  << Comment.create!(comment: 'comment4')

    [book_one, book_three, article_one].each(&:save)

    assert_equal ['Article1'], Article.titles_for_comments(Comment.ids)
    assert_equal %w[Book1 Book3], Book.titles_for_comments(Comment.ids)
    assert_equal %w[Article1 Book1 Book3], Comment.distinct_titles.sort
  end
end