Argon generates a workflow engine (built around a state machine)
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Argon is a workflow engine for Rails, built around a state machine. It relies on a state propery on a model to manage workflow around state transitions.


Add this line to your application's Gemfile:

gem 'argon'

And then execute:

$ bundle

Or install it yourself as:

$ gem install argon


The Argon module provides a state_machine class method which expects the following args (as demonstrated by the example below).

  class Report
    include Argon

    def on_cancel(action:, message:)
      # This is called from inside the lock, after the edge transitions, with the name of the action. If an exception is thrown here, the entire transition is rolled back

    def after_cancel(action:, message:)
      # This is called after a successful transition, with the action which actually succeeded

    state_machine state: {
      states: {
        draft:     0,
        submitted: 1,
        approved:  2,
        rejected:  3,
        cancelled: 4,
      events: [
      edges: [
        { from: :draft,     to: :submitted, action: :submit,           callbacks: {on: false, after: false}                                                     },
        { from: :draft,     to: :cancelled, action: :cancel_draft,     callbacks: {on: false, after: false}, on_events: [:cancel], parameters: [:message_param] },
        { from: :submitted, to: :cancelled, action: :cancel_submitted, callbacks: {on: false, after: false}, on_events: [:cancel], parameters: [:message_param] },
      parameters: {
        message_param: {
          name:   :message,
          check:  ->(message) { !message.nil? },
      on_successful_transition: ->(from:, to:) { /* Do something here */ },
      on_failed_transition:     ->(from:, to:) { /* Do something else */ },

Report#state will now return one of :draft, :submitted, :approved, :rejected or :cancelled. There is no method to set the state directly, and it is recommended to set the numberical value of the initial state (e.g. 0 here for :draft) as the default value of the state column for the reports table, which should be an integer column.

This will generate the following methods for the states:

  • Report.draft, Report.submitted, Report.approved, Report.rejected, and Report.cancelled : These are scopes similar to the ones generated by Rails enum
  • Report#draft?, Report#submitted?, Report#approved?, Report#rejected?, and Report#cancelled? : These are query methods similar to the ones generated by Rails enum

The following methods are generated from the edges:

  • Report#submit! : This will move the state to submitted if the object was in the draft state. The state change is done inside a lock (ActiveRecord::Locking::Pessimistic#with_lock). If was true, then Report#on_submit is called from within the lock. If was true, then Report#after_submit will be called, after the lock is released. Note that if enabled, the callbacks have to be defined before state_machine is called, or an exception will be raised.

  • Report#can_submit? : This will return true if the object was in the draft state.

    (similar methods are created for cancel_draft and cancel_submitted)

The following method will be generated for the event:

  • Report#cancel! : This will check can_cancel_draft?, and if true, will call cancel_draft!. Else, it will try can_cancel_submitted?, and call cancel_submitted! if true, and so on. Note that for event methods, both callbacks are mandatory (i.e. here, both on_cancel and after_cancel must be defined before state_machine is called).


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Argon project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.