create_or_find_by.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"
  gem "pg"
end

require "active_record"
require "minitest/autorun"
require "logger"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "postgresql", database: "rails")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
  end

  create_table :comments, force: true do |t|
    t.integer :post_id
  end

  add_index :comments, :post_id, unique: true
end

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

class BugTest < Minitest::Test
  def test_primary_key_growth
    post_one = Post.create!
    post_two = Post.create!

    comment_one_post_one = Comment.create_or_find_by(post: post_one)
    assert_equal 1, comment_one_post_one.id

    # Create fails and it finds comment_one_post_one
    comment_two_post_one = Comment.create_or_find_by(post: post_one)
    assert_equal 1, comment_two_post_one.id
    assert_equal comment_two_post_one, comment_one_post_one

    comment_one_post_two = Comment.create_or_find_by(post: post_two)
    assert_equal 2, comment_one_post_two
  end
end