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https://github.com/troessner/transitions

State machine extracted from ActiveModel
https://github.com/troessner/transitions

Last synced: about 2 months ago
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State machine extracted from ActiveModel

Host: GitHub
URL: https://github.com/troessner/transitions
Owner: troessner
License: mit
Created: 2010-02-20T14:30:30.000Z (over 14 years ago)
Default Branch: master
Last Pushed: 2022-03-31T10:12:04.000Z (over 2 years ago)
Last Synced: 2024-07-06T02:31:32.404Z (3 months ago)
Language: Ruby
Homepage:
Size: 299 KB
Stars: 535
Watchers: 14
Forks: 95
Open Issues: 6
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE.txt

Awesome Lists containing this project

awesome-ruby-toolbox - Transitions - Lightweight state machine extracted from ActiveModel (Rails Plugins / State Machines)
awesome-ruby - transitions - A ruby state machine implementation. (State Machines)

README

### Overview
[![Build status](https://secure.travis-ci.org/troessner/transitions.png?branch=master)](http://travis-ci.org/troessner/transitions)
[![Gem Version](https://badge.fury.io/rb/transitions.png)](http://badge.fury.io/rb/transitions)
[![Code Climate](https://codeclimate.com/github/troessner/transitions.png)](https://codeclimate.com/github/troessner/transitions)
[![Dependency Status](https://gemnasium.com/troessner/transitions.png)](https://gemnasium.com/troessner/transitions)
[![Inline docs](http://inch-ci.org/github/troessner/transitions.png)](http://inch-ci.org/github/troessner/transitions)

### Synopsis

`transitions` is a ruby state machine implementation.

### Installation

#### Rails

This goes into your Gemfile:
```ruby
gem "transitions", :require => ["transitions", "active_model/transitions"]
```

… and this into your ORM model:
```ruby
include ActiveModel::Transitions
```

#### Standalone
```shell
gem install transitions
```

… and this into your class:
```ruby
include Transitions
```

### Using transitions
```ruby
class Product
include ActiveModel::Transitions

state_machine do
state :available # first one is initial state
state :out_of_stock, :exit => :exit_out_of_stock
state :discontinued, :enter => lambda { |product| product.cancel_orders }

event :discontinued do
transitions :to => :discontinued, :from => [:available, :out_of_stock], :on_transition => :do_discontinue
end
event :out_of_stock, :success => :reorder do
transitions :to => :out_of_stock, :from => [:available, :discontinued]
end
event :available do
transitions :to => :available, :from => [:out_of_stock], :guard => lambda { |product| product.in_stock > 0 }
end
end
end
```
In this example we assume that you are in a rails project using Bundler, which
would automatically require `transitions`. If this is not the case then you
have to add
```ruby
require 'transitions'
```

wherever you load your dependencies in your application.

**Known limitations:**

* You can only use one state machine per model. While in theory you can
define two or more, this won't work as you would expect. Not supporting
this was intentional, if you're interested in the rational look up version
0.1.0 in the CHANGELOG.

* Use symbols, not strings for declaring the state machine. Using strings is
**not** supported as is using whitespace in names (because `transitions`
possibly generates methods out of this).

### Features

#### Getting and setting the current state

Use the (surprise ahead) `current_state` method - in case you didn't set a
state explicitly you'll get back the state that you defined as initial state.
```ruby
>> Product.new.current_state
=> :available
```

You can also set a new state explicitly via `update_current_state(new_state,
persist = true / false)` but you should never do this unless you really know
what you're doing and why - rather use events / state transitions (see below).

Predicate methods are also available using the name of the state.
```ruby
>> Product.new.available?
=> true
```

#### Events

When you declare an event, say `discontinue`, three methods are declared for
you: `discontinue`, `discontinue!` and `can_discontinue?`. The first two
events will modify the `state` attribute on successful transition, but only
the bang(!)-version will call `save!`. The `can_discontinue?` method will not
modify state but instead returns a boolean letting you know if a given
transition is possible.

In addition, a `can_transition?` method is added to the object that expects one or more event names as arguments. This semi-verbose method name is used to avoid collisions with [https://github.com/ryanb/cancan](the authorization gem CanCan).
```ruby
>> Product.new.can_transition? :out_of_stock
=> true
```

If you need to get all available transitions for the current state you can simply call:
```ruby
>> Product.new.available_transitions
=> [:discontinued, :out_of_stock]
```

#### Callback overview

`transitions` offers you the possibility to define a couple of callbacks during the different stages / places of transitioning from one state to another. So let's say you have an event `discontinue` which transitions the current state from `in_stock` to `sold_out`. The callback sequence would look like this:

| discontinue event |
|
|
|
| current_state `in_stock` | ----> executes `exit` callback
|
|
|
| current_state `in_stock` | ----> executes `on_transition` callback if and only the `guard` check was successfull. If not successfull, the chain aborts here and the `event_failed` callback is executed
|
|
|
| current_state `in_stock` | ----> executes `enter` callback for new state `sold_out`
|
|
|
| current_state `in_stock` | ----> executes `event_fired` callback
|
|
|
| current_state `in_stock` | ----> move state from `in_stock` to `sold_out`
|
|
|
| current_state `sold_out` | ----> executes `success` callback of the `discontinue` event

This all looks very complicated (I know), but don't worry, in 99% of all cases you don't have to care about the details and the usage itself is straightforward as you can see in the examples below where each callback is explained a little more throrough.

#### Callback # 1: State callbacks `enter` and `exit`

If you want to trigger a method call when the object enters or exits a state regardless
of the transition that made that happen, use `enter` and `exit`.

`exit` will be called before the transition out of the state is executed. If you want the method
to only be called if the transition is successful, then use another approach.

`enter` will be called after the transition has been made but before the object is persisted. If you want
the method to only be called after a successful transition to a new state including persistence,
use the `success` argument to an event instead.

An example:

```ruby
class Motor < ActiveRecord::Base
include ActiveModel::Transitions

state_machine do
state :off, enter: :turn_power_off
state :on, exit: :prepare_shutdown
end
end
```

#### Callback # 2: Transition callback `on_transition`

Each event definition takes an optional `on_transition` argument, which allows
you to execute code on transition. This callback is executed after the `exit` callback of the former state (if it has been defined) but before the `enter` callback of the new state and only if the `guard` check succeeds. There is no check if the callback itself succeeds (meaning that `transitions` does not evaluate its return value somewhere). However, you can easily add some properly abstracted error handling yourself by raising an exception in this callback and then handling this exception in the (also defined by you) `event_failed` callback (see below and / or the wonderful ascii diagram above).

You can pass in a Symbol, a String, a Proc or an Array containing method names
as Symbol or String like this:
```ruby
event :discontinue do
transitions :to => :discontinued, :from => [:available, :out_of_stock], :on_transition => [:do_discontinue, :notify_clerk]
end
```

Any arguments passed to the event method will be passed on to the `on_transition` callback.

#### Callback #3 : Event callback `success`

In case you need to trigger a method call after a successful transition you
can use `success`. This will be called after the `save!` is complete (if you
use the `state_name!` method) and should be used for any methods that require
that the object be persisted.
```ruby
event :discontinue, :success => :notify_admin do
transitions :to => :discontinued, :from => [:available, :out_of_stock]
end
```

In addition to just specify the method name on the record as a symbol you can
pass a lambda to perfom some more complex success callbacks:
```ruby
event :discontinue, :success => lambda { |order| AdminNotifier.notify_about_discontinued_order(order) } do
transitions :to => :discontinued, :from => [:available, :out_of_stock]
end
```

If you need it, you can even call multiple methods or lambdas just passing an
array:
```ruby
event :discontinue, :success => [:notify_admin, lambda { |order| AdminNotifier.notify_about_discontinued_order(order) }] do
transitions :to => :discontinued, :from => [:available, :out_of_stock]
end
```

#### Callback caveats

Since callbacks will not be called by you but by `transitions` the scope is different when they are called and you'll run into problems if you use classes / modules in those callbacks that have the same names like `transitions` ones, e.g. "Event":

```Ruby
def event_fired(current_state, new_state, event)
Event.create!
end
```

This will crash because `transitions` uses an Event class as well, and, since the scope has changed when `transitions` calls this method, `transitions` will use it's own Event class here, not yours.
In this case you can try to prefix your models with the "::" operator and see if that solves your problems. See https://github.com/troessner/transitions/issues/123 for details.

#### Automatic scope generation

`transitions` will automatically generate scopes for you if you are using
ActiveRecord and tell it to do so via the `auto_scopes` option:

Given a model like this:
```ruby
class Order < ActiveRecord::Base
include ActiveModel::Transitions
state_machine :auto_scopes => true do
state :pick_line_items
state :picking_line_items
event :move_cart do
transitions to: :pick_line_items, from: :picking_line_items
end
end
end
```

you can use this feature a la:
```ruby
>> Order.pick_line_items
=> []
>> Order.create!
=> #
>> Order.pick_line_items
=> [#]
```

#### Using `guard`

Each event definition takes an optional `guard` argument, which acts as a
predicate for the transition.

You can pass in Symbols, Strings, or Procs like this:
```ruby
event :discontinue do
transitions :to => :discontinued, :from => [:available, :out_of_stock], :guard => :can_discontinue
end
```

or
```ruby
event :discontinue do
transitions :to => :discontinued, :from => [:available, :out_of_stock], :guard => [:can_discontinue, :super_sure?]
end
```

Any arguments passed to the event method will be passed on to the `guard`
predicate.

Note that guards will **not** raise on failure on their own. This means that if you want to
treat the failure of a guard exceptional you'll need to raise an exception yourself explicitly
in that guard (see [here](https://github.com/troessner/transitions/issues/149) for the
corresponding discussion).

#### Timestamps

If you'd like to note the time of a state change, Transitions comes with
timestamps free! To activate them, simply pass the `timestamp` option to the
event definition with a value of either true or the name of the timestamp
column. *NOTE - This should be either true, a String, a Symbol, or an Array of
these*
```ruby
# This will look for an attribute called exploded_at or exploded_on (in that order)
# If present, it will be updated
event :explode, :timestamp => true do
transitions :from => :complete, :to => :exploded
end

# This will look for an attribute named repaired_on to update upon save
event :rebuild, :timestamp => :repaired_on do
transitions :from => :exploded, :to => :rebuilt
end
```

#### Using `event_fired` and `event_failed`

In case you define `event_fired` and / or `event_failed`, `transitions` will
use those callbacks correspondingly.

You can use those callbacks like this:
```ruby
def event_fired(current_state, new_state, event)
MyLogger.info "Event fired #{event.inspect}"
end

def event_failed(event)
MyLogger.warn "Event failed #{event.inspect}"
end
```

#### Listing all the available states and events

You can easily get a listing of all available states:
```ruby
Order.available_states # Uses the default state machine
# => [:pick_line_items, :picking_line_items]
```

Same goes for the available events:
```ruby
Order.available_events
# => [:move_cart]
```

#### Explicitly setting the initial state with the `initial` option
```ruby
state_machine :initial => :closed do
state :open
state :closed
end
```

The explicitly specified state **must** be one of the states listed in the state definition below, otherwise `transitions` will raise a rather unhelpful exception like "NoMethodError: undefined method `call_action' for nil:NilClass" (there's a ticket to fix this already: https://github.com/troessner/transitions/issues/112)

### Configuring a different column name with ActiveRecord

To use a different column than `state` to track it's value simply do this:
```ruby
class Product < ActiveRecord::Base
include Transitions

state_machine :attribute_name => :different_column do

...

end
end
```

### Ruby Compatibility

Supported versions:

* 2.1
* 2.2

Supported implementations:

* MRI
* Rubinius
* Jruby

### Supported Rails versions:

* 3
* 4

### Known bugs / limitations

* Right now it seems like `transitions` does not play well with `mongoid`. A
possible fix had to be rolled back due to other side effects:
https://github.com/troessner/transitions/issues/76. Since I know virtually
zero about mongoid, a pull request would be highly appreciated.
* Multiple state machines are not and will not be supported. For the rationale
behind this see the Changelog.

### Associated projects

* [GraphvizTransitions](https://github.com/itkin/graphviz_transitions) - Adds support for generating graphs based on states, events and transitions

### Documentation, Guides & Examples

* [Online API Documentation](http://rdoc.info/github/troessner/transitions/master/Transitions)
* [Railscasts #392: A Tour of State Machines](http://railscasts.com/episodes/392-a-tour-of-state-machines) (requires Pro subscription)