Demonstrates a bug on ActiveRecord that occurs when one uses `Model.where(....).first_or_create(....)`. The `where(....)` is used also in any `Model.query` that takes place before the `first_or_create! returns. In the following test, the last assertion fails.

bug_on_active_record_when_first_or_create

unless File.exist?('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'

# 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 do |t|
    t.string  :isbn,        :null => false
    t.string  :name,        :null => false
    t.string  :author,      :null => false
    t.integer :book_count, :null => false

    t.timestamps
  end
  add_index :books, [:isbn]
end

class Book < ActiveRecord::Base
  before_create :count_books

  protected

  def count_books
    self.book_count = Book.count
    logger.info "Number of Books: #{Book.count}"
    logger.info "Books where isbn equals x, sql is: #{Book.where(:isbn => 'x').to_sql}"
  end
end

class BugTest < MiniTest::Unit::TestCase
  def test_scope_query_while_on_first_or_create
    book = nil
    number_of_books_before = Book.count
    book = Book.create!(:isbn => '1', :name => 'name1', :author => 'author1')
    number_of_books_after = Book.count
    assert_equal 1, number_of_books_after
    assert_equal 0, book.book_count
	
    book = Book.create!(:isbn => '2', :name => 'name2', :author => 'author2')
    number_of_books_after = Book.count
    assert_equal 2, number_of_books_after
    assert_equal 1, book.book_count
	
    book = Book.create!(:isbn => '3', :name => 'name3', :author => 'author3')
    number_of_books_after = Book.count
    assert_equal 3, number_of_books_after
    assert_equal 2, book.book_count

    book = Book.where(:isbn => ' 4').first_or_create!(
                      :name => 'name4',
                      :author => 'author3'
	)
    number_of_books_after = Book.count
    assert_equal 4, number_of_books_after
    assert_equal 3, book.book_count	
  end
end