gistfile1.rb

unless File.exist?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    gem 'rails', github: 'rails/rails'
    gem 'arel', github: 'rails/arel'
    gem 'rack', github: 'rack/rack'
    gem 'i18n', github: 'svenfuchs/i18n'
    gem 'sqlite3'
  GEMFILE

  system 'bundle'
end

require 'bundler'
Bundler.setup(:default)

require 'active_record'
require "#{`bundle show activerecord`.chomp}/test/cases/test_case"
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 :posts do |t|
  end

  create_table :comments do |t|
    t.integer :post_id
    t.boolean :is_best
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

class Post < ActiveRecord::Base
  has_many :comments
  has_one :best_comment, -> { where(is_best: true) }, class_name: Comment
end

class BugTest < ActiveRecord::TestCase
  def test_eager_load_uses_single_query
    Post.create!.tap do |post|
      post.comments << Comment.create!(is_best: true)
    end
    Post.create!
    assert_queries 1 do
      Post.eager_load(:best_comment).map{|post| post.best_comment}
    end
  end
end