Note: you can find documentation for specific workflow rubygem versions at http://rubygems.org/gems/workflow : select a version (optional, default is latest release), click "Documentation" link. When reading on github.com, the README refers to the upcoming release.
Workflow is a finite-state-machine-inspired API for modeling and interacting with what we tend to refer to as 'workflow'.
A lot of business modeling tends to involve workflow-like concepts, and the aim of this library is to make the expression of these concepts as clear as possible, using similar terminology as found in state machine theory.
So, a workflow has a state. It can only be in one state at a time. When a workflow changes state, we call that a transition. Transitions occur on an event, so events cause transitions to occur. Additionally, when an event fires, other arbitrary code can be executed, we call those actions. So any given state has a bunch of events, any event in a state causes a transition to another state and potentially causes code to be executed (an action). We can hook into states when they are entered, and exited from, and we can cause transitions to fail (guards), and we can hook in to every transition that occurs ever for whatever reason we can come up with.
Now, all that’s a mouthful, but we’ll demonstrate the API bit by bit with a real-ish world example.
Let’s say we’re modeling article submission from journalists. An article is written, then submitted. When it’s submitted, it’s awaiting review. Someone reviews the article, and then either accepts or rejects it. Here is the expression of this workflow using the API:
class Article
include Workflow
workflow do
state :new do
event :submit, :transitions_to => :awaiting_review
end
state :awaiting_review do
event :review, :transitions_to => :being_reviewed
end
state :being_reviewed do
event :accept, :transitions_to => :accepted
event :reject, :transitions_to => :rejected
end
state :accepted
state :rejected
end
endNice, isn’t it!
Note: the first state in the definition (:new in the example, but you
can name it as you wish) is used as the initial state - newly created
objects start their life cycle in that state.
Let’s create an article instance and check in which state it is:
article = Article.new
article.accepted? # => false
article.new? # => trueYou can also access the whole current_state object including the list
of possible events and other meta information:
article.current_state
=> #<Workflow::State:0x7f1e3d6731f0 @events={
:submit=>#<Workflow::Event:0x7f1e3d6730d8 @action=nil,
@transitions_to=:awaiting_review, @name=:submit, @meta={}>},
name:new, meta{}
You can also check, whether a state comes before or after another state (by the order they were defined):
article.current_state # => being_reviewed
article.current_state < :accepted # => true
article.current_state >= :accepted # => false
article.current_state.between? :awaiting_review, :rejected # => trueNow we can call the submit event, which transitions to the
:awaiting_review state:
article.submit!
article.awaiting_review? # => trueEvents are actually instance methods on a workflow, and depending on the state you’re in, you’ll have a different set of events used to transition to other states.
It is also easy to check, if a certain transition is possible from the
current state . article.can_submit? checks if there is a :submit
event (transition) defined for the current state.
gem install workflowImportant: If you’re interested in graphing your workflow state machine, you will also need to
install the activesupport and ruby-graphviz gems.
Versions up to and including 1.0.0 are also available as a single file download - lib/workflow.rb file.
After installation or downloading the library you can easily try out all the example code from this README in irb.
$ irb require 'rubygems' require 'workflow'
Now just copy and paste the source code from the beginning of this README file snippet by snippet and observe the output.
The best way is to use convention over configuration and to define a method with the same name as the event. Then it is automatically invoked when event is raised. For the Article workflow defined earlier it would be:
class Article
def reject
puts 'sending email to the author explaining the reason...'
end
endarticle.review!; article.reject! will cause state transition to
being_reviewed state, persist the new state (if integrated with
ActiveRecord), invoke this user defined reject method and finally
persist the rejected state.
Note: on successful transition from one state to another the workflow
gem immediately persists the new workflow state with update_column(),
bypassing any ActiveRecord callbacks including updated_at update.
This way it is possible to deal with the validation and to save the
pending changes to a record at some later point instead of the moment
when transition occurs.
You can also define event handler accepting/requiring additional arguments:
class Article
def review(reviewer = '')
puts "[#{reviewer}] is now reviewing the article"
end
end
article2 = Article.new
article2.submit!
article2.review!('Homer Simpson') # => [Homer Simpson] is now reviewing the articleAlternative way is to use a block (only recommended for short event implementation without further code nesting):
event :review, :transitions_to => :being_reviewed do |reviewer|
# store the reviewer
endWe’ve noticed, that mixing the list of events and states with the blocks invoked for particular transitions leads to a bumpy and poorly readable code due to a deep nesting. We tried (and dismissed) lambdas for this. Eventually we decided to invoke an optional user defined callback method with the same name as the event (convention over configuration) as explained before.
Note: Workflow 2.0 is a major refactoring for the worklow library.
If your application suddenly breaks after the workflow 2.0 release, you’ve
probably got your Gemfile wrong ;-). workflow uses
semantic versioning.
For highest compatibility please reference the desired major minor version.
Note on ActiveRecord/Rails 4.*, 5.\* Support:
Since integration with ActiveRecord makes over 90% of the issues and maintenance effort, and also to allow for an independent (faster) release cycle for Rails support, starting with workflow version 2.0 in January 2019 the support for ActiveRecord (4.*, 5.\* and newer) has been extracted into a separate gem. Read at workflow-activerecord, how to include the right gem.
To use legacy built-in ActiveRecord 2.3 - 4.* support, reference Workflow 1.2 in your Gemfile:
gem 'workflow', '~> 1.2'
If you do not use a relational database and ActiveRecord, you can still
integrate the workflow very easily. To implement persistence you just
need to override load_workflow_state and
persist_workflow_state(new_value) methods. Next section contains an example for
using CouchDB, a document oriented database.
Tim Lossen implemented support for remodel / redis key-value store.
We are using the compact couchtiny library here. But the implementation would look similar for the popular couchrest library.
require 'couchtiny'
require 'couchtiny/document'
require 'workflow'
class User < CouchTiny::Document
include Workflow
workflow do
state :submitted do
event :activate_via_link, :transitions_to => :proved_email
end
state :proved_email
end
def load_workflow_state
self[:workflow_state]
end
def persist_workflow_state(new_value)
self[:workflow_state] = new_value
save!
end
endPlease also have a look at the full source code.
I get a lot of requests to integrate persistence support for different databases, object-relational adapters, column stores, document databases.
To enable highest possible quality, avoid too many dependencies and to
avoid unneeded maintenance burden on the workflow core it is best to
implement such support as a separate gem.
Only support for the ActiveRecord will remain for the foreseeable
future. So Rails beginners can expect workflow to work with Rails out
of the box. Other already included adapters stay for a while but should
be extracted to separate gems.
If you want to implement support for your favorite ORM mapper or your
favorite NoSQL database, you just need to implement a module which
overrides the persistence methods load_workflow_state and
persist_workflow_state. Example:
module Workflow
module SuperCoolDb
module InstanceMethods
def load_workflow_state
# Load and return the workflow_state from some storage.
# You can use self.class.workflow_column configuration.
end
def persist_workflow_state(new_value)
# save the new_value workflow state
end
end
module ClassMethods
# class methods of your adapter go here
end
def self.included(klass)
klass.send :include, InstanceMethods
klass.extend ClassMethods
end
end
endThe user of the adapter can use it then as:
class Article
include Workflow
include Workflow:SuperCoolDb
workflow do
state :submitted
# ...
end
endI can then link to your implementation from this README. Please let me
also know, if you need any interface beyond load_workflow_state and
persist_workflow_state methods to implement an adapter for your
favorite database.
Conditions can be a "method name symbol" with a corresponding instance method, a proc or lambda which are added to events, like so:
state :off
event :turn_on, :transition_to => :on,
:if => :sufficient_battery_level?
event :turn_on, :transition_to => :low_battery,
:if => proc { |device| device.battery_level > 0 }
end
# corresponding instance method
def sufficient_battery_level?
battery_level > 10
endWhen calling a device.can_<fire_event>? check, or attempting a device.<event>!, each event is checked in turn:
-
With no
:ifcheck, proceed as usual. -
If an
:ifcheck is present, proceed if it evaluates to true, or drop to the next event. -
If you’ve run out of events to check (eg.
battery_level == 0), then the transition isn’t possible.
You can also pass additional arguments, which can be evaluated by :if methods or procs. See examples in conditionals_test.rb
We already had a look at the declaring callbacks for particular workflow
events. If you would like to react to all transitions to/from the same state
in the same way you can use the on_entry/on_exit hooks. You can either define it
with a block inside the workflow definition or through naming
convention, e.g. for the state :pending just define the method
on_pending_exit(new_state, event, *args) somewhere in your class.
If you want to be informed about everything happening everywhere, e.g. for
logging then you can use the universal on_transition hook:
workflow do
state :one do
event :increment, :transitions_to => :two
end
state :two
on_transition do |from, to, triggering_event, *event_args|
Log.info "#{from} -> #{to}"
end
endIf you want to do custom exception handling internal to workflow, you can define an on_error hook in your workflow.
For example:
workflow do
state :first do
event :forward, :transitions_to => :second
end
state :second
on_error do |error, from, to, event, *args|
Log.info "Exception(#{error.class}) on #{from} -> #{to}"
end
endIf forward! results in an exception, on_error is invoked and the workflow stays in a 'first' state. This capability
is particularly useful if your errors are transient and you want to queue up a job to retry in the future without
affecting the existing workflow state.
If you want to halt the transition conditionally, you can just raise an
exception in your [transition event handler](#transition_event_handler).
There is a helper called halt!, which raises the
Workflow::TransitionHalted exception. You can provide an additional
halted_because parameter.
def reject(reason)
halt! 'We do not reject articles unless the reason is important' \
unless reason =~ /important/i
endThe traditional halt (without the exclamation mark) is still supported
too. This just prevents the state change without raising an
exception.
You can check halted? and halted_because values later.
The whole event sequence is as follows:
-
before_transition
-
event specific action
-
on_transition (if action did not halt)
-
on_exit
-
PERSIST WORKFLOW STATE (i.e. transition) or on_error
-
on_entry
-
after_transition
You can easily reflect on workflow specification programmatically - for the whole class or for the current object. Examples:
article2.current_state.events # lists possible events from here
article2.current_state.events[:reject].transitions_to # => :rejected
Article.workflow_spec.states.keys
#=> [:rejected, :awaiting_review, :being_reviewed, :accepted, :new]
Article.workflow_spec.state_names
#=> [:rejected, :awaiting_review, :being_reviewed, :accepted, :new]
# list all events for all states
Article.workflow_spec.states.values.collect &:eventsYou can also store and later retrieve additional meta data for every state and every event:
class MyProcess
include Workflow
workflow do
state :main, :meta => {:importance => 8}
state :supplemental, :meta => {:importance => 1}
end
end
puts MyProcess.workflow_spec.states[:supplemental].meta[:importance] # => 1The workflow library itself uses this feature to tweak the graphical representation of the workflow. See below.
For an advance example please see workflow_from_json_test.rb.
In case you have very extensive workflow definition or would like to reuse
workflow definition for different classes, you can include parts like in
the including a child workflow definition example.
You can generate a graphical representation of the workflow for
a particular class for documentation purposes.
Use Workflow::create_workflow_diagram(class) in your rake task like:
namespace :doc do
desc "Generate a workflow graph for a model passed e.g. as 'MODEL=Order'."
task :workflow => :environment do
require 'workflow/draw'
Workflow::Draw::workflow_diagram(ENV['MODEL'].constantize)
end
endsudo apt-get install graphviz # Linux
brew install graphviz # Mac OS
cd workflow
gem install bundler
bundle install
# run all the tests
bundle exec rake test-
❏ unit tests for the new behavior provided: new tests fail without you change, all tests succeed with your change
-
❏ documentation update included
ActiveAdmin-Workflow - is an integration with ActiveAdmin.
Author: Vladimir Dobriakov, https://infrastructure-as-code.de
Copyright (c) 2010-2024 Vladimir Dobriakov and Contributors
Copyright (c) 2008-2009 Vodafone
Copyright (c) 2007-2008 Ryan Allen, FlashDen Pty Ltd
Based on the work of Ryan Allen and Scott Barron
Licensed under MIT license, see the MIT-LICENSE file.
