#update on CPK association requires an explicit reload to work correctly

[jarl-dk]

Steps to reproduce

Save the below script as ar.rb and run

ruby ar.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 "sqlite3"
end

require "active_record"
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 :books, force: true, primary_key: %i[number] do |t|
    t.integer :number
    t.string :title
    t.integer :main_chapter_number, null: true
  end

  create_table :chapters, force: true, primary_key: %i[book_number number] do |t|
    t.integer :book_number
    t.integer :number
    t.string :title
  end

  add_foreign_key :books, :chapters, column: [:number, :main_chapter_number], primary_key: [:book_number, :number]
end

class Book < ActiveRecord::Base
  self.primary_key = %i[number]
  has_many :chapters,
           foreign_key: :book_number,
           inverse_of: :book

  belongs_to :main_chapter, class_name: "Chapter",
             query_constraints: %i[number main_chapter_number],
             optional: true,
             inverse_of: :book
end

class Chapter < ActiveRecord::Base
  self.primary_key = %i[book_number number]

  belongs_to :book, foreign_key: :book_number, inverse_of: :chapters
end

class BugTest < Minitest::Test
  def test_association_stuff
    book = Book.create!(number: 1, title: "First book")

    book.chapters << Chapter.new(book:, number: 1, title: "Chapter one") << Chapter.new(book:, number: 2, title: "Chapter two")

    assert_equal 2, book.chapters.count
    assert_equal 2, Chapter.count
    assert_equal nil, book.main_chapter_number

    book.update!(main_chapter: book.chapters.first)
    assert_equal 1, book.main_chapter_number

    # book.reload # This is a workaround that will make it work, but it should not be necessary

    book.update!(main_chapter_number: nil) # This one will not update the database.
    assert_equal nil, book.main_chapter_number
  end
end

Expected behavior

I expect

1 runs, 5 assertions, 0 failures, 0 errors, 0 skips

Actual behavior

It fails with

Failure:
BugTest#test_association_stuff [ar.rb:72]:
Expected: nil
  Actual: 1

See comment in script for workaround

System configuration

Rails version: main

Ruby version: 3.2.2

Maybe related issues: #49597

[jarl-dk]

cc/ @nvasilevski can you take a look at this?

[iamradioactive]

@jarl-dk , This issue is similar to the one addressed by #50297. The root cause for this one seems to be related to the stale state detection. I tested your script against that branch and can confirm it fixes the issue. You can verify the same using the following.

gem "rails", github: "iamradioactive/rails", branch: "handle_composite_foreign_keys"

Let me know if I missed something.

[jarl-dk]

I confirm that my script works against that branch.

[iamradioactive]

@jarl-dk , Since the PR is not merged yet, I think instead of closing this issue we should keep it open or maybe mark as duplicate. I can go ahead and update the PR description to include that this issue will be fixed as well.