3903.rb

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

  system 'bundle'
end

require 'bundler'
Bundler.setup(:default)

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

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :users, :force => true do |t|
    t.integer :projects_count, :default => 0
  end

  create_table :projects, :force => true do |t|
    t.integer :users_count, :default => 0
  end
  
  create_table :memberships, :force => true do |t|
    t.integer :user_id
    t.integer :project_id
  end
end

class User < ActiveRecord::Base
  has_many :memberships
  has_many :projects, :through => :memberships
end

class Project < ActiveRecord::Base
  has_many :memberships
  has_many :users, :through => :memberships
end

class Membership < ActiveRecord::Base
  belongs_to :user
  belongs_to :project, counter_cache: :users_count
end

class BugTest < MiniTest::Unit::TestCase
  def test_case
    Membership.delete_all

    user = User.create
    project = Project.create

    assert_equal 0, user.projects_count
    assert_equal 0, project.users_count

    user.projects << project

    user.reload
    project.reload

    assert_equal 1, user.projects_count
    assert_equal 1, project.users_count
  end
end