Ruby on Rails Finite State Machine Plugin: acts_as_state_machine

adzdavies

A few points:
# On calling of an event! method, acts_as_state_machine calls “update_attribute”. If you check the api docs, it calls ’save’ (not save! - so no exception raised), and furthermore BY-PASSES validations altogether.

The result?
You might want to guard with ‘valid?’ or call ’save!’ yourself in combination with the ‘event!’ method.

# As another consequence, your callback sequence is ever so slightly wrong:
* acts_as_state_machine :enter showering
* ActiveRecord::Base.before_save
* ActiveRecord::Base.save
* acts_as_state_machine :after showering
* ActiveRecord::Base.after_save
* acts_as_state_machine :exit sleeping

It will call after_save, _then_ the :after, then the :exit callbacks (at least in my version of acts_as_state_machine

However, you are 100% right with newly created records - because acts_as_state_machine uses ‘before_create’ callback.

BTW - Thanks for blogging - not enough info out there on this great little plugin!

Cheers,
Adam

T

Thanks for the great tutorial! One question though: is there a way to pass an argument to an event callback? I have a model for which I want to log a history record every time it changes state. The problem is, I need to pass a user specified date from the controller to be part of the history record.

Bottom line, I need to do something like this:

state :sleeping,
:enter => :get_into_bed,
:after => Proc.new {|model| model.whack_alarm_clock }

def get_into_bed
BedtimeHistory.create(:date_of_sleep => input_date_from_user)
end

Is it possible to get the input_date_from_user into the get_into_bed function?

Chetan Patil

Hi,
Thanks for the writeup. It helped me get started with acts_as_state_machine.

I made some enhancements to the plugin which are described here (using your example):
http://justbarebones.blogspot.com/2007/11/actsasstatemachine-enhancements.html

- c

Noah

Thanks for this. I also extended this useful plugin a tiny bit.

What if you want to execute something after every state transition? (say, for logging the change) Currently, that would require something like

state :one, :after => :logit
state :two, :after => :logit
…

Intead I wrote some code so that you can set all these up at once in the initial call:
acts_as_state_machine :initial => :created, :column => ’status’, :after => :logit

The same pattern could be applied for other callbacks as well. Email me at noahd1 at yahoo dot com for the code (pretty simple) if interested.

Noah

Hi Jason -

You sent me an email, but thought I’d respond here as well.

I think the kind of logic you’re suggesting really belongs in a controller and not in the state machine. So your controller logic would look more like:

unless params[:log_message].blank?
@person.log_message= #messge to be logged
@person.switch_to_happy! #state change
else
# throw an error … return back to user
end

If that doesn’t suit you, I would look into using a guard on the transition:

transitions :from => :sad, :to => :happy, :guard => Proc.new {|o| o.valid? }

though, how to throw back an error without rechecking that the object is valid again, I’m not entirely sure.

Adam

Hello,

I was wondering if there is a way to override the :initial state…or simply not have an initial. I have an :initial state of :pending in my Friendship model, however, i want to create friendship record with the state :accepted. I’ve tried Friendship.create(:state => “accepted”) and creating a new object using .new, setting the state, and calling save!, but when the record initially saves, :pending is set as the status.

Is there anyway to fix this so i do not have to save the record, refetch, change the state, and resave?

Dave

One potential gotcha is that invalid transitions return an empty array, rather than raise false or an exception.

For example:

state :fooish
state :barish
state :bazish

event :bar do
transitions :from => :fooish, :to => :bar
end

something.state = ‘baz’
something.bar! #=> []

A quick monkey patch would overload Event::fire(record):

def fire(record)
next_states = next_states(record) # line added
return false if next_states.empty? # line added
next_states.each do |transition| # line edited
break true if transition.perform(record)
end
end

something.state = ‘baz’
something.bar! #=> false

D

Tom Harrison

This is a really great tutorial. Thanks. You might want to check into your host, or perhaps something on the page here; it took a good 10 minutes to load for me. Then again, I had plenty to absorb as I did read

tayfun

Many thanks for the enlightening article.

Here are some intricacies I believe I cannot describe well:

>> person = Person.new
=> #
>> person.shower!
NoMethodError: You have a nil object when you didn’t expect it!

But,

>> person.state = ‘working’
=> “working”
>> person
=> #
>> person.shower!
=> true
>> person
=> #

It’s still sleeping in the end! So what I understand is that it doesn’t matter what you do until the record is saved. It will still be initialized like it is defined no matter what events you call before.

I guess in the end it’s not good setting the default value through migrations like you say in the article. It will not matter when it is saved.

Good day.

Nick Poulden

Thanks for this really useful article. I’ve been looking for some good documentation for this plugin for a while!

dkmenace

Has anyone got this plugin working with Rails 2.0.X?

Resonante

Epales!

how can i list the states on the view ?

Help!

thanks.

Erik Petersen

Just a addendum, the :enter callback takes a proc or symbol, the :after and :exit callbacks take a proc or an array of symbols thus you can chain callbacks:

:after => [:this, :then, :that] # => Yes!
:enter => [:that, :then, :this] # => No!

Thanks for the writeup!

Josh Aronson

What you refer to as adjectives are actually non-finite verb forms, or gerunds.