A simple workflow system using state machines

A simple workflow systemDavid Petersonpeterson@orbitec.com.auWhat is a workflow? A process that moves through a sequence of steps (from start and finish) in order to performsome functionExamples׏ Fulfilling an order● Publishing documents / content● Approving a requestA few things in common ...● Typically multi-step● Performed asynchronously● May be long-running● Steps may be conditional● Each step may need to do an operationThe IdeaMany simple workflowscan be modelled as afinite state machine(Not all)acts_as_state_machine● AASM to friends!● Rails plugin by Scott Barron● Provides:●A simple FSM implementation●A DSL for expressing FSM in Ruby codehttp://elitists.textdriven.com/svn/plugins/acts_as_state_machine/trunk/# Basic workflow exampleclass ActionWorkflow < ActiveRecord::Base acts_as_state_machine :initial => :created, :column => 'status' state :created state :approved state :rejected state :cancelled event :approve { transitions :to => :approved, :from => :created } event :cancel { transitions :to => :cancelled, :from =>[:created, :approved, :rejected] } ...endAASM provides some methods● An action! method for each event● A query? method for each stateExamples: workflow.approve! # moves to approved state workflow.cancelled? # Returns booleanGuards event :approve { transitions :to => :approved, :from => :created, :guard => Proc.new {|w| !w.expired?}}● Allows conditions on transitions● Transition is not available unless condition is met● Some conditions may be expressed best in your code, not in guards