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true end end state :parked, :stalled, :idling do def moving? false end end end state_machine :alarm_state, initial: :active, namespace: :'alarm' do event :enable do transition all => :active end event :disable do transition all => :off end state :active, :value => 1 state :off, :value => 0 end def initialize @seatbelt_on = false @time_used = 0 @auto_shop_busy = true super() # NOTE: This *must* be called, otherwise states won't get initialized end def put_on_seatbelt @seatbelt_on = true end def passed_inspection? false end def tow # tow the vehicle end def fix # get the vehicle fixed by a mechanic end def log_start_failure # log a failed attempt to start the vehicle end end ``` **Note** the comment made on the `initialize` method in the class. In order for state machine attributes to be properly initialized, `super()` must be called. See `StateMachines:MacroMethods` for more information about this. Using the above class as an example, you can interact with the state machine like so: ```ruby vehicle = Vehicle.new # => #<Vehicle:0xb7cf4eac @state="parked", @seatbelt_on=false> vehicle.state # => "parked" vehicle.state_name # => :parked vehicle.human_state_name # => "parked" vehicle.parked? # => true vehicle.can_ignite? # => true vehicle.ignite_transition # => #<StateMachines:Transition attribute=:state event=:ignite from="parked" from_name=:parked to="idling" to_name=:idling> vehicle.state_events # => [:ignite] vehicle.state_transitions # => [#<StateMachines:Transition attribute=:state event=:ignite from="parked" from_name=:parked to="idling" to_name=:idling>] vehicle.speed # => 0 vehicle.moving? # => false vehicle.ignite # => true vehicle.parked? # => false vehicle.idling? # => true vehicle.speed # => 10 vehicle # => #<Vehicle:0xb7cf4eac @state="idling", @seatbelt_on=true> vehicle.shift_up # => true vehicle.speed # => 10 vehicle.moving? # => true vehicle # => #<Vehicle:0xb7cf4eac @state="first_gear", @seatbelt_on=true> # A generic event helper is available to fire without going through the event's instance method vehicle.fire_state_event(:shift_up) # => true # Call state-driven behavior that's undefined for the state raises a NoMethodError vehicle.speed # => NoMethodError: super: no superclass method `speed' for #<Vehicle:0xb7cf4eac> vehicle # => #<Vehicle:0xb7cf4eac @state="second_gear", @seatbelt_on=true> # The bang (!) operator can raise exceptions if the event fails vehicle.park! # => StateMachines:InvalidTransition: Cannot transition state via :park from :second_gear # Generic state predicates can raise exceptions if the value does not exist vehicle.state?(:parked) # => false vehicle.state?(:invalid) # => IndexError: :invalid is an invalid name # Namespaced machines have uniquely-generated methods vehicle.alarm_state # => 1 vehicle.alarm_state_name # => :active vehicle.can_disable_alarm? # => true vehicle.disable_alarm # => true vehicle.alarm_state # => 0 vehicle.alarm_state_name # => :off vehicle.can_enable_alarm? # => true vehicle.alarm_off? # => true vehicle.alarm_active? # => false # Events can be fired in parallel vehicle.fire_events(:shift_down, :enable_alarm) # => true vehicle.state_name # => :first_gear vehicle.alarm_state_name # => :active vehicle.fire_events!(:ignite, :enable_alarm) # => StateMachines:InvalidParallelTransition: Cannot run events in parallel: ignite, enable_alarm # Human-friendly names can be accessed for states/events Vehicle.human_state_name(:first_gear) # => "first gear" Vehicle.human_alarm_state_name(:active) # => "active" Vehicle.human_state_event_name(:shift_down) # => "shift down" Vehicle.human_alarm_state_event_name(:enable) # => "enable" # States / events can also be references by the string version of their name Vehicle.human_state_name('first_gear') # => "first gear" Vehicle.human_state_event_name('shift_down') # => "shift down" # Available transition paths can be analyzed for an object vehicle.state_paths # => [[#<StateMachines:Transition ...], [#<StateMachines:Transition ...], ...] vehicle.state_paths.to_states # => [:parked, :idling, :first_gear, :stalled, :second_gear, :third_gear] vehicle.state_paths.events # => [:park, :ignite, :shift_up, :idle, :crash, :repair, :shift_down] # Find all paths that start and end on certain states vehicle.state_paths(:from => :parked, :to => :first_gear) # => [[ # #<StateMachines:Transition attribute=:state event=:ignite from="parked" ...>, # #<StateMachines:Transition attribute=:state event=:shift_up from="idling" ...> # ]] # Skipping state_machine and writing to attributes directly vehicle.state = "parked" vehicle.state # => "parked" vehicle.state_name # => :parked # *Note* that the following is not supported (see StateMachines:MacroMethods#state_machine): # vehicle.state = :parked ``` ## Additional Topics ### Explicit vs. Implicit Event Transitions Every event defined for a state machine generates an instance method on the class that allows the event to be explicitly triggered. Most of the examples in the state_machine documentation use this technique. However, with some types of integrations, like ActiveRecord, you can also *implicitly* fire events by setting a special attribute on the instance. Suppose you're using the ActiveRecord integration and the following model is defined: ```ruby class Vehicle < ActiveRecord::Base state_machine initial: :parked do event :ignite do transition parked: :idling end end end ``` To trigger the `ignite` event, you would typically call the `Vehicle#ignite` method like so: ```ruby vehicle = Vehicle.create # => #<Vehicle id=1 state="parked"> vehicle.ignite # => true vehicle.state # => "idling" ``` This is referred to as an *explicit* event transition. The same behavior can also be achieved *implicitly* by setting the state event attribute and invoking the action associated with the state machine. For example: ```ruby vehicle = Vehicle.create # => #<Vehicle id=1 state="parked"> vehicle.state_event = 'ignite' # => 'ignite' vehicle.save # => true vehicle.state # => 'idling' vehicle.state_event # => nil ``` As you can see, the `ignite` event was automatically triggered when the `save` action was called. This is particularly useful if you want to allow users to drive the state transitions from a web API. See each integration's API documentation for more information on the implicit approach. ### Symbols vs. Strings In all of the examples used throughout the documentation, you'll notice that states and events are almost always referenced as symbols. This isn't a requirement, but rather a suggested best practice. You can very well define your state machine with Strings like so: ```ruby class Vehicle state_machine initial: 'parked' do event 'ignite' do transition 'parked' => 'idling' end # ... end end ``` You could even use numbers as your state / event names. The **important** thing to keep in mind is that the type being used for referencing states / events in your machine definition must be **consistent**. If you're using Symbols, then all states / events must use Symbols. Otherwise you'll encounter the following error: ```ruby class Vehicle state_machine do event :ignite do transition parked: 'idling' end end end # => ArgumentError: "idling" state defined as String, :parked defined as Symbol; all states must be consistent ``` There **is** an exception to this rule. The consistency is only required within the definition itself. However, when the machine's helper methods are called with input from external sources, such as a web form, state_machine will map that input to a String / Symbol. For example: ```ruby class Vehicle state_machine initial: :parked do event :ignite do transition parked: :idling end end end v = Vehicle.new # => #<Vehicle:0xb71da5f8 @state="parked"> v.state?('parked') # => true v.state?(:parked) # => true ``` **Note** that none of this actually has to do with the type of the value that gets stored. By default, all state values are assumed to be string -- regardless of whether the state names are symbols or strings. If you want to store states as symbols instead you'll have to be explicit about it: ```ruby class Vehicle state_machine initial: :parked do event :ignite do transition parked: :idling end states.each do |state| self.state(state.name, :value => state.name.to_sym) end end end v = Vehicle.new # => #<Vehicle:0xb71da5f8 @state=:parked> v.state?('parked') # => true v.state?(:parked) # => true ``` ### Syntax flexibility Although state_machine introduces a simplified syntax, it still remains backwards compatible with previous versions and other state-related libraries by providing some flexibility around how transitions are defined. See below for an overview of these syntaxes. #### Verbose syntax In general, it's recommended that state machines use the implicit syntax for transitions. However, you can be a little more explicit and verbose about transitions by using the `:from`, `:except_from`, `:to`, and `:except_to` options. For example, transitions and callbacks can be defined like so: ```ruby class Vehicle state_machine initial: :parked do before_transition from: :parked, except_to: :parked, do: :put_on_seatbelt after_transition to: :parked do |vehicle, transition| vehicle.seatbelt = 'off' end event :ignite do transition from: :parked, to: :idling end end end ``` #### Transition context Some flexibility is provided around the context in which transitions can be defined. In almost all examples throughout the documentation, transitions are defined within the context of an event. If you prefer to have state machines defined in the context of a **state** either out of preference or in order to easily migrate from a different library, you can do so as shown below: ```ruby class Vehicle state_machine initial: :parked do ... state :parked do transition to: :idling, :on => [:ignite, :shift_up], if: :seatbelt_on? def speed 0 end end state :first_gear do transition to: :second_gear, on: :shift_up def speed 10 end end state :idling, :first_gear do transition to: :parked, on: :park end end end ``` In the above example, there's no need to specify the `from` state for each transition since it's inferred from the context. You can also define transitions completely outside the context of a particular state / event. This may be useful in cases where you're building a state machine from a data store instead of part of the class definition. See the example below: ```ruby class Vehicle state_machine initial: :parked do ... transition parked: :idling, :on => [:ignite, :shift_up] transition first_gear: :second_gear, second_gear: :third_gear, on: :shift_up transition [:idling, :first_gear] => :parked, on: :park transition [:idling, :first_gear] => :parked, on: :park transition all - [:parked, :stalled]: :stalled, unless: :auto_shop_busy? end end ``` Notice that in these alternative syntaxes: * You can continue to configure `:if` and `:unless` conditions * You can continue to define `from` states (when in the machine context) using the `all`, `any`, and `same` helper methods ### Static / Dynamic definitions In most cases, the definition of a state machine is **static**. That is to say, the states, events and possible transitions are known ahead of time even though they may depend on data that's only known at runtime. For example, certain transitions may only be available depending on an attribute on that object it's being run on. All of the documentation in this library define static machines like so: ```ruby class Vehicle state_machine :state, initial: :parked do event :park do transition [:idling, :first_gear] => :parked end ... end end ``` However, there may be cases where the definition of a state machine is **dynamic**. This means that you don't know the possible states or events for a machine until runtime. For example, you may allow users in your application to manage the state machine of a project or task in your system. This means that the list of transitions (and their associated states / events) could be stored externally, such as in a database. In a case like this, you can define dynamically-generated state machines like so: ```ruby class Vehicle attr_accessor :state # Make sure the machine gets initialized so the initial state gets set properly def initialize(*) super machine end # Replace this with an external source (like a db) def transitions [ {parked: :idling, on: :ignite}, {idling: :first_gear, first_gear: :second_gear, on: :shift_up} # ... ] end # Create a state machine for this vehicle instance dynamically based on the # transitions defined from the source above def machine vehicle = self @machine ||= Machine.new(vehicle, initial: :parked, action: :save) do vehicle.transitions.each {|attrs| transition(attrs)} end end def save # Save the state change... true end end # Generic class for building machines class Machine def self.new(object, *args, &block) machine_class = Class.new machine = machine_class.state_machine(*args, &block) attribute = machine.attribute action = machine.action # Delegate attributes machine_class.class_eval do define_method(:definition) { machine } define_method(attribute) { object.send(attribute) } define_method("#{attribute}=") {|value| object.send("#{attribute}=", value) } define_method(action) { object.send(action) } if action end machine_class.new end end vehicle = Vehicle.new # => #<Vehicle:0xb708412c @state="parked" ...> vehicle.state # => "parked" vehicle.machine.ignite # => true vehicle.machine.state # => "idling vehicle.state # => "idling" vehicle.machine.state_transitions # => [#<StateMachines:Transition ...>] vehicle.machine.definition.states.keys # => :first_gear, :second_gear, :parked, :idling ``` As you can see, state_machine provides enough flexibility for you to be able to create new machine definitions on the fly based on an external source of transitions. ## Dependencies Ruby versions officially supported and tested: * Ruby (MRI) 2.0.0+ * JRuby * Rubinius For graphing state machine: * [state_machines-graphviz](http://github.com/state-machines/state_machines-graphviz) For documenting state machines: * [state_machines-yard](http://github.com/state-machines/state_machines-yard) ## TODO * Add matchers/assertions for rspec and minitest ## Contributing 1. Fork it ( https://github.com/state-machines/state_machines/fork ) 2. Create your feature branch (`git checkout -b my-new-feature`) 3. Commit your changes (`git commit -am 'Add some feature'`) 4. Push to the branch (`git push origin my-new-feature`) 5. Create a new Pull Request |
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