This package contains AASM, a library for adding finite state machines to Ruby classes.
AASM started as the acts_as_state_machine plugin but has evolved into a more generic library that no longer targets only ActiveRecord models. It currently provides adapters for ActiveRecord and Mongoid, but it can be used for any Ruby class, no matter what parent class it has (if any).
Adding a state machine is as simple as including the AASM module and start defining states and events together with their transitions:
class Job
include AASM
aasm do
state :sleeping, :initial => true
state :running
state :cleaning
event :run do
transitions :from => :sleeping, :to => :running
end
event :clean do
transitions :from => :running, :to => :cleaning
end
event :sleep do
transitions :from => [:running, :cleaning], :to => :sleeping
end
end
endThis provides you with a couple of public methods for instances of the class Job:
job = Job.new
job.sleeping? # => true
job.may_run? # => true
job.run
job.running? # => true
job.sleeping? # => false
job.may_run? # => false
job.run # => raises AASM::InvalidTransitionIf you don't like exceptions and prefer a simple true or false as response, tell
AASM not to be whiny:
class Job
...
aasm :whiny_transitions => false do
...
end
end
job.running? # => true
job.may_run? # => false
job.run # => falseYou can define a number of callbacks for your transitions. These methods will be called, when certain criteria are met, like entering a particular state:
class Job
include AASM
aasm do
state :sleeping, :initial => true, :before_enter => :do_something
state :running
event :run, :after => Proc.new { |user| notify_somebody(user) } do
transitions :from => :sleeping, :to => :running, :on_transition => Proc.new {|obj, *args| obj.set_process(*args) }
end
event :sleep do
after do
...
end
error do |e|
...
end
transitions :from => :running, :to => :sleeping
end
end
def set_process(name)
...
end
def do_something
...
end
def notify_somebody(user)
...
end
endIn this case do_something is called before actually entering the state sleeping,
while notify_somebody is called after the transition run (from sleeping to running)
is finished.
Here you can see a list of all possible callbacks, together with their order of calling:
event:before
previous_state:before_exit
new_state:before_enter
...update state...
previous_state:after_exit
new_state:after_enter
event:afterAlso, you can pass parameters to events:
job = Job.new
job.run(:running, :defragmentation)In this case the set_process would be called with :defagmentation argument.
In case of an error during the event processing the error is rescued and passed to :error
callback, which can handle it or re-raise it for further propagation.
Let's assume you want to allow particular transitions only if a defined condition is
given. For this you can set up a guard per transition, which will run before actually
running the transition. If the guard returns false the transition will be
denied (raising AASM::InvalidTransition or returning false itself):
class Job
include AASM
aasm do
state :sleeping, :initial => true
state :running
state :cleaning
event :run do
transitions :from => :sleeping, :to => :running
end
event :clean do
transitions :from => :running, :to => :cleaning
end
event :sleep do
transitions :from => :running, :to => :sleeping, :guard => :cleaning_needed?
end
end
def cleaning_needed?
false
end
end
job = Job.new
job.run
job.may_sleep? # => false
job.sleep # => raises AASM::InvalidTransitionAASM comes with support for ActiveRecord and allows automatical persisting of the object's state in the database.
class Job < ActiveRecord::Base
include AASM
aasm do # default column: aasm_state
state :sleeping, :initial => true
state :running
event :run do
transitions :from => :sleeping, :to => :running
end
event :sleep do
transitions :from => :running, :to => :sleeping
end
end
endYou can tell AASM to auto-save the object or leave it unsaved
job = Job.new
job.run # not saved
job.run! # savedSaving includes running all validations on the Job class. If you want make sure
the state gets saved without running validations (and thereby maybe persisting an
invalid object state), simply tell AASM to skip the validations:
class Job < ActiveRecord::Base
include AASM
aasm :skip_validation_on_save => true do
state :sleeping, :initial => true
state :running
event :run do
transitions :from => :sleeping, :to => :running
end
event :sleep do
transitions :from => :running, :to => :sleeping
end
end
endAASM also supports persistence to Mongodb if you're using Mongoid. Make sure to include Mongoid::Document before you include AASM.
class Job
include Mongoid::Document
include AASM
aasm do
...
end
endAASM will automatically create scope methods for each state in the model.
class Job < ActiveRecord::Base
include AASM
aasm do
state :sleeping, :initial => true
state :running
state :cleaning
end
def sleeping
"This method name is in already use"
end
endclass JobsController < ApplicationController
def index
@running_jobs = jobs.running
@recent_cleaning_jobs = jobs.cleaning.where('created_at >= ?', 3.days.ago)
# @sleeping_jobs = jobs.sleeping #=> "This method name is in already use"
end
endIf you don't need scopes (or simply don't want them), disable their creation when
defining the AASM states, like this:
class Job < ActiveRecord::Base
include AASM
aasm :create_scopes => false do
state :sleeping, :initial => true
state :running
state :cleaning
end
endSince version 3.0.13 AASM supports ActiveRecord transactions. So whenever a transition callback or the state update fails, all changes to any database record are rolled back. Mongodb does not support transactions.
If you want to make sure a depending action happens only after the transaction is committed,
use the after_commit callback, like this:
class Job < ActiveRecord::Base
include AASM
aasm do
state :sleeping, :initial => true
state :running
event :run, :after_commit => :notify_about_running_job do
transitions :from => :sleeping, :to => :running
end
end
def notify_about_running_job
...
end
endAs a default AASM uses the column aasm_state to store the states. You can override
this by defining your favorite column name, using :column like this:
class Job < ActiveRecord::Base
include AASM
aasm :column => 'my_state' do
...
end
endWhatever column name is used, make sure to add a migration to provide this column
(of type string):
class AddJobState < ActiveRecord::Migration
def self.up
add_column :jobs, :aasm_state, :string
end
def self.down
remove_column :jobs, :aasm_state
end
endAASM supports a couple of methods to find out which states or events are provided or permissible.
Given the Job class from above:
job = Job.new
job.aasm.states
=> [:sleeping, :running, :cleaning]
job.aasm.states(:permissible => true)
=> [:running]
job.run
job.aasm.states(:permissible => true)
=> [:cleaning, :sleeping]
job.aasm.events
=> [:run, :clean, :sleep]% gem install aasm# Gemfile
gem 'aasm'% rake build
% sudo gem install pkg/aasm-x.y.z.gemLook at the CHANGELOG for details.
Feel free to
- create an issue on GitHub
- ask a question on StackOverflow (tag with
aasm) - send us a tweet @aasm
This software is provided "as is" and without any express or implied warranties, including, without limitation, the implied warranties of merchantibility and fitness for a particular purpose.
Copyright (c) 2006-2012 Scott Barron
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The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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