Old gem state_machine

Definition with:

class Objects
  state_machine :state, initial: :my_state do

Inside definition you can use:

  • before_transition on: :my_state, after_transition on: :my_state
  • after_failure on: :my_state
  • around_transition

  • event :my_event { transition :my_state, :my_other_state, if: Proc.new { |my_object| my_object.valid? } }
  • state :my_state do end

In transitions you can use keyword all or any to match all/any states, and same to match same state (usefull when you have list of matched states). You can use object.my_state? to check if it is currently in that my_state. Also you can use object.can_my_event? to check if it can change state using this event. Also object.fire_state_event(:my_event) and object.state?(:my_state). You can use bang method to raise error if event fails object.my_event!. List of all possible events is object.state_events (or object.status_events to list all events for status column).

To list of all states you can use Post.state_machines[:status].states.map &:name

You can use namespace state_machine :alarm_state, initial: :active, namespace: :alarm do when all events and states have prefix alarm_my_state and suffix my_event_alarm.

Instead of calling the event explicitly you can use object.state_event = "my_event"; object.save to trigger event. You can manually change state but then you will break state machine, so better is to update state_event. On creation, initial state event is triggered, so you will have two events (from nil to initial, and from initial to the value of state_event).

You can define transitions inside the context of an event. First transition that matches the state and passes its conditions will be used.

event :repair do
  transition stalled: :parked, unless: :auto_shop_busy
  transition stalled: same

but also you can define transition inside the context of state. Than you do not need to use :from (since we know the state) but you need :on

state :parked do
  transition to: :idling, on: [:ignite, :shift_up], if: :seatbelt_on?
  def speed

When defining transitions instead of using hash rocket syntax you can use :from, :except_from, :to and :except_to options

before_transition :parked => any - :parked, :do => :put_on_seatbelt
# is the same as
before_transition :from => :parked, :except_to => :parked, :do => :put_on_seatbelt

You can generate graph with

sudo apt-get install graphviz
echo "gem 'ruby-graphviz', require: 'graphviz'" >> Gemfile
rake state_machine:draw CLASS=Customer,Location HUMAN_NAMES=true
gnome-open Location_status.png

Old gem state_machine-audit_trail

cat "gem 'state_machine-audit_trail'" >> Gemfile
rails generate state_machines:audit_trail Post status

This will generate model and migration which you can update

# app/models/post_status_transition.rb
class PostStatusTransition < ActiveRecord::Base
  belongs_to :post
# db/migrate/123123123123_create_post_status_transitions.rb
class CreatePostStatusTransitions < ActiveRecord::Migration[5.1]
  def change
    create_table :post_status_transitions do |t|
      t.references :post, foreign_key: true
      # t.string :namespace # this is for new version of state_machines
      t.string :event
      t.string :from
      t.string :to
      # add your custom fields
      t.string :change_description
      t.text :comment
      t.timestamp :created_at

If you need more data you need to add more columns, for example change_description (by server) and comment (by user) which are defined as attr_accessor :change_description, :comment in model and populated in form or before_transition. For other fields that you want to track, those columns need to exists in table.

class Post < ApplicationRecord
  state_machine :status, initial: :walk do
    store_audit_trail context_to_log: :comment
    event :start do
      transition all => :run
    event :stop do
      transition all => :walk

Upgrade gem state_machines

New gem have some breaking changes. You need is to include additional gem that will use hooks to initialize data

cat >> Gemfile << HERE_DOC
gem "state_machines"
gem 'state_machines-activerecord'

Before audit trail was adding description on .save, but in new gem, it is adding on .new action and values are memoized


Also, before we could use Post.where(name: 'my name', status: :enabled).first_or_create event we had state_machine :status, initial: :created_new. Now post will create with Post.last.status # => 'initial'

For audit trail you need to do some renaming https://github.com/state-machines/state_machines-audit_trail/wiki/Converting-from-former-state_machine-audit_trail-to-state_machines-audit_trail

cat >> Gemfile << HERE_DOC
gem 'state_machines-audit_trail'

New version rails g state_machines:audit_trail Post status will generate same migration with additional column: t.string :namespace. Note that you should use singular Post and not plural Posts

For additional fiels that you want to store, you can use real columns, but its easier to use some description which you can generate from other fields.

  before_transition :on => any do |object, transition|
    case transition.event
    when :start
      self.description = "My object started"

In model you need

class Post < ApplicationRecord
  attr_accessor :change_description, :comment
  state_machine :status, initial: :walk do
    audit_trail context: [:change_description, :comment, :name]
    event :start do
      transition all => :run
    event :stop do
      transition all => :walk

  def description=(text)
    @description = "My associated #{page.name} : #{text}"

  def description
    # note that this is called on Post.new, so you should have page parameter
    # Post.new; Post.new; will call this twice, but without associated page
    # Post.new post_params.merge(page_id: current_page)
    @description ||= "My associated #{page.name}"

In your view

  <% post.status_events.each do |event| %>
    <%= link_to event, action_post_path(post, event: event), method: :post %>
  <% end %>

  # or on update form
  <%= form.select :status_event, post.status_events %>

  # of in hidden field on form object
  <%= form.hidden_field :status_event, value: :edit %>

  # or plain input (no need for :value key)
  <%= hidden_field_tag :status_event, :edit %>

And controller

  def action
    @post.fire_status_event params[:event]
    redirect_to posts_path

  # or on update form
    :name, :description, :status_event
    updated_from_ip: request.remote_ip,
    updated_by: current_user,

You can use Constant.POST_STATUSES # { CREATED_NEW: "Created new" } to list all statuses and events in one file. Than in transition you can use transition all - Constant.POST_STATUSES.slice(:CREATED_NEW) => same

Conditional validation callbacks hooks works fine if it is rails validates but if it is customer validation validate :my_method than it won’t work in multiple states https://github.com/state-machines/state_machines-activerecord#state-driven-validations so instead of

state :first_gear, :second_gear do
  validate :speed_is_legal
state :first_gear, :second_gear do
  validate {|vehicle| vehicle.speed_is_legal}

Note that whole event change is wrapped in transaction, so if state validation fails everything will be rolledback.

(short notation might rise expection ‘no receiver given’)

# if this line raises exception
# than use longer syntax
validate { |location| location.check? }

If you want to validate specific event advance_renewal (event without corresponding state) so you can not use event :advance_renewal; transition all => same, if: Proc.new { |m| m.has_advance_package? } since at the show time if does not have advance package so m.can_advance_renewal #=> false. So you need to use rails validate validate :advance_renewal_settings, on: [:update], if: :advance_renewal? and def advance_renewal_settings; errors.add(:advance_renewal_package, "Please select Advance Renewal Package.")unless advance_renewal_package.present?; end.

before_transition and after_transition callbacks

Other audit gems

  • paper_trail
    bundle exec rails g paper_trail:install --with-changes
    bundle exec rake db:migrate

    in model


    You can set custom event

    a.paper_trail_event = 'update title'
    a.update title: 'new'
    a.versions.last.event # 'update title'

    To see changes

    # { changed_column => [before, after], updated_at => DateTime }
    # {"full_name"=>["member_profile", "first change"], "updated_at"=>[Tue, 27 Jul 2021 06:27:31.493388000 UTC +00:00, Tue, 27 Jul 2021 06:28:07.407190000 UTC +00:00]}
    # to see all changes
    puts PaperTrail::Version.all.map(&:changeset).join"\n"
    # to see all changes for particular object in console
    o.versions.map {|v| v.changeset.each {|k,v| puts "#{k}: #{v.first.nil? ? 'nil' : v.first} -> #{v.second.nil? ? 'nil' : v.second}" } } && nil

    In test use helper https://github.com/paper-trail-gem/paper_trail#7-testing

    # in config/environments/test.rb
    config.after_initialize do
      PaperTrail.enabled = false
    # in test/test_helper.rb
    def with_versioning
      was_enabled = PaperTrail.enabled?
      was_enabled_for_request = PaperTrail.request.enabled?
      PaperTrail.enabled = true
      PaperTrail.request.enabled = true
        PaperTrail.enabled = was_enabled
        PaperTrail.request.enabled = was_enabled_for_request
    test 'something that needs versioning' do
      with_versioning do
        # your test

    When using uuid you need to change type for item_id https://github.com/paper-trail-gem/paper_trail/issues/363#issuecomment-249080184

    def change
      create_table :versions do |t|
        t.string   :item_type, null: false
        t.uuid     :item_id,   null: false

    Sometimes new versions is not save, I do not know why I got o.versions # => [] or there exists versions that I have not created.

    PaperTrail::Version.all.map &:item_type
    PaperTrail::Version.all.map &:item_id
    PaperTrail::Version.all.map &:item