Demonstrate counter_cache/destroy callback race condition

counter_cache_test.rb

require 'rubygems'
require 'active_record'

ActiveRecord::Base.establish_connection("adapter" => "sqlite3", "database" => ":memory:")

class Widget < ActiveRecord::Base
  connection.create_table table_name do |t|
    t.string :name
    t.integer :thing_count
  end unless table_exists?
  
  has_many :things
end

class Thing < ActiveRecord::Base
  connection.create_table table_name do |t|
    t.integer :widget_id
    t.string :name
  end unless table_exists?
  
  belongs_to :widget, :counter_cache => :thing_count
end

widget = Widget.create!(:name => "test")
thing_1 = widget.things.create!(:name => "one")
thing_2 = widget.things.create!(:name => "two")

widget.reload
puts "widget has #{widget.things.size} things (#{widget.thing_count} in counter cache)"

t1 = Thing.find(thing_1.id)
t2 = Thing.find(thing_1.id)

puts "destroy thing #{t1.name}"
t1.destroy
widget.reload
puts "widget has #{widget.things.size} things (#{widget.thing_count} in counter cache)"

puts "destroy thing #{t1.name} (again)"
t2.destroy
widget.reload
puts "widget has #{widget.things.size} things (#{widget.thing_count} in counter cache)"