rails_bug_has_many_through_with_foreign_key.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'
  gem 'activerecord', '4.2.0'
  gem 'sqlite3'
end

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

Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table "categories" do |t|
    t.string   "name"
  end

  create_table "product_categories" do |t|
    t.integer  "product_id"
    t.integer  "category_id"
  end

  create_table "products" do |t|
    t.string   "name"
  end
end

class Product < ActiveRecord::Base
  has_many :product_categories, foreign_key: 'product_id' # remove foreign_key and it works
  has_many :categories, through: :product_categories
end

class ProductCategory < ActiveRecord::Base
  belongs_to :product
  belongs_to :category
  
  validates :product, :category, presence: true
end

class Category < ActiveRecord::Base
  has_many :product_categories
  has_many :products, through: :product_categories
end

class BugTest < Minitest::Test
  def test_association_stuff
    c = Category.new(name: 'Electronic')
    assert c.save, c.errors.full_messages
    p = Product.new(name: 'Smartphone', categories: [c])
    assert p.save, p.errors.full_messages #=> ["Product categories is invalid"]
  end
end