What's the best way to automatically change state in AASM

Question

I've been using AASM to make state machines in my current project and was wondering what's the best way to automatically call events and proceed to the next state?

I am considering 2 ways of doing this:

1. Setup a background job to periodically check if certain conditions are met, hence call the event to proceed to the next state.

2. Have a before_save call a method that tries the next event in succession. With a guard on it, it won't succeed if conditions are met, otherwise, state changes and next time Model is updated, we check for a new event.

I was leaning towards the second option as setting up a background_job queue just to transition events seems like an overkill. I couldn't find best practices regarding this, so I would love to know the best approach and why it is so?

Example

For example we have start_onboarding and complete_onboarding events. I don't want to manually call these events, but I want to automatically transition between pending -> in_progress -> completed events.

  enum status: {
    pending: 1,
    in_progress: 2,
    completed: 3
  }

  aasm column: :status, enum: true, whiny_transitions: false do
    state :pending, initial: true
    state :in_progress
    state :completed

    event :start_onboarding do
      transitions from: :pending, to: :in_progress
    end

    event :complete_onboarding do
      transitions from: :in_progress,
                  to: :completed,
                  if: :onboarding_completed?
    end
  end

Answer 1

In the similar task:

We got rid of:

• Callbacks to switch states because they bring performance degrade
• A live polling (with background jobs) because it also bring performance degrade

We come to using:

• Service objects
• Scheduled jobs

And the code was looking something like this:

require 'active_record'
require 'aasm'
require 'sidekiq'

class Task < ActiveRecord::Base
  include AASM

  establish_connection adapter: 'sqlite3', database: 'todo.db'

  connection.create_table table_name, force: true do |t|
    t.string   :name,       null: false
    t.string   :aasm_state, null: false, index: true
    t.datetime :expired_at, null: false
  end

  validates :name, :aasm_state, :expired_at, presence: true

  aasm do
    state :pending, initial: true
    state :in_progress
    state :completed
    state :expired

    event :run do
      transitions to: :in_progress
    end

    event :complete do
      transitions to: :completed
    end

    event :expire do
      transitions to: :expired, unless: :completed?
    end
  end
end

class Task::ExpireJob
  include Sidekiq::Worker

  def perform task
    task.expire!
  end
end

class Task::CreationService
  def self.create! params
    task = Task.create! params
    task.run!
    Task::ExpireJob.perform_at task.expired_at, task
    task
  end

  def self.complete! task
    task.complete!
    task
  end
end

task = Task::CreationService.create! \
  name:       'first',
  expired_at: DateTime.now + 30.seconds

p task
p Task::CreationService.complete! task