Lingceng's Blog

Tips About Using AASM Gem

Recently, I’m using aasm gem to do order production status control. Here I have some tips about using aasm gem.

I’m using aasm 4.5.0 and rails 4.2.0. First, I post a snippet here for better explaination.

order.rb 
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class Order
  include AASM

  aasm column: :production_status do
    state :idle, initial: true
    state :at_center
    state :ready

    after_all_transitions :_save_production_status_change

    event :check_in, before: :set_current_step_to_center, guard: :_status_fit do
      transitions from: [:idle], to: :at_center, after: :_change_status_to_repairing
    end

    event :to_ready, before: :set_current_step, guard: :_status_fit do
      transitions from: [:at_center, :idle], to: :ready, after: :_change_status_to_repairing
    end
    ...
  end

  ...
end

How to keep actions in transaction?

Of course, you can acheive it by wrapping actions in a transaction. eg.

Order.transaction do
  order.check_in
  order.save
end

However, aasm also provide a bang method to acheive it. eg.

order.check_in!

But the two forms is not the same.

Please take care the save point if you choose to use order.check_in!. order.check_in! internally calls save after new_state enter callback. So, changes in callbacks after new_state enter will not auto-save.

See the list of callbacks.

begin
  event           before
  event           guards
  transition      guards
  old_state       before_exit
  old_state       exit
                  after_all_transitions
  transition      after
  new_state       before_enter
  new_state       enter
  ...update state...               # here is the save point
  event         success            # if persist successful
  old_state       after_exit
  new_state       after_enter
  event           after
rescue
  event           error
end

Let’s see a example. If I wrote the check_in event like following:

event :check_in, before: :set_current_step_to_center, guard: :_status_fit,
  after: :_change_status_to_repairing do
  transitions from: [:idle], to: :at_center
end

def _change_status_to_repairing
  status = 'repairing'
end

The _change_status_to_repairing is at event after callback. So, when I run order.check_in!, order.status will not persist.

order.check_in!
order.reload.status == 'repairing'
# => false

Of cause, you can call save in _change_status_to_repairing But the order will be persisted even when you run non-bang method order.check_in.

def _change_status_to_repairing
  status = 'repairing'
  save
end

Oh. Maybe you should choose to use the first form.

Avoid using Proc.new with optional argument in guards and callbacks

See https://github.com/aasm/aasm/issues/293

Take care of before event filter

See https://github.com/aasm/aasm/issues/294

duplicate global callbacks caused by after_all_transitions

See https://github.com/aasm/aasm/issues/297

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