Optimistic Locking in Rails: Preventing outdated updates

rails_optimistic_locking_example.rb

# Run with `ruby rails_optimistic_locking_example.rb`
#
# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # gem "rails", github: "rails/rails", branch: "main"
  gem 'rails', '~> 6.1', '>= 6.1.3.2'
  gem "sqlite3"
end

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 :products, force: true do |t|
    t.string :name
    t.string :description
    t.integer :weight_grams
    t.integer :price_cents
  end

  create_table :product_with_lockings, force: true do |t|
    t.string :name
    t.string :description
    t.integer :weight_grams
    t.integer :price_cents
    t.integer :lock_version
  end
end

class Product < ActiveRecord::Base
end

class ProductWithLocking < ActiveRecord::Base
end


class ProductUpdateTest < Minitest::Test
  PERMITTED_PARAM_NAMES = ['name', 'description', 'weight_grams', 'price_cents']

  def setup
    #1 We create a new product
    @new_product = Product.create(name: "Book")

    # Data loaded in the form of edit pages after creation
    edit_page_form = @new_product.attributes.slice(*PERMITTED_PARAM_NAMES)

    #2 Someone updates that product
    Product
      .find(@new_product.id)
      .update!(edit_page_form.merge( # Like handling submitted form data
                                    'description' => 'The greatest story ever told',
                                    'price_cents' => 70_00
                                   ))

    #3 We also update the product on our old tab
    Product
      .find(@new_product.id)
      .update!(edit_page_form.merge('weight_grams' => 314))

    @actual_product = Product.find(@new_product.id)
  end

  def test_product_name_saved
    refute_nil @actual_product.name        # => ✅
  end

  def test_product_weight_saved
    refute_nil @actual_product.weight_grams # => ✅
  end

  def test_product_description_saved
    refute_nil @actual_product.description  # => ❌
  end

  def test_product_price_saved
    refute_nil @actual_product.price_cents  # => ❌
  end
end

class ProductWithLockingUpdateTest < Minitest::Test
  # IMPORTANT: `lock_version` should be included in the form data
  PERMITTED_PARAM_NAMES = ['name', 'description', 'weight_grams', 'price_cents', 'lock_version']

  def setup
    #1 We create a new product
    @new_product = ProductWithLocking.create(name: "Book")

    # Data loaded in the form of edit pages after creation
    @edit_page_form = @new_product.attributes.slice(*PERMITTED_PARAM_NAMES)

    #2 Someone updates that product
    ProductWithLocking
      .find(@new_product.id)
      .update!(@edit_page_form.merge( # Like handling submitted form data
                                    'description' => 'The greatest story ever told',
                                    'price_cents' => 70_00
                                   ))
  end

  # Now you aren't allowed to update if the version doesn't match
  def test_updating_with_old_version
    assert_raises ActiveRecord::StaleObjectError do
      ProductWithLocking
        .find(@new_product.id)
        .update(@edit_page_form.merge('weight_grams' => 314))
    end
  end
end