state_machine
状态机管理类的行为
通常，一个 对象 处于何种状态常常取决于一系列 boolean 判断，根据 ‘判断值’ 来确定。
当你有多个类 都存在 这种需求 时，处理起来就会变得很累赘 和 烦嗦。
state_machine简化这种设计：一个真实的状态机(state_machine)包括状态states，事件events，转换 transitions和回调callbacks。
该API的设计是如此简单，你甚至都不需要(真正理解)什么状态机是:)
包含能各种 模块 的支持，现在我们只关心 Rails 中(默认)的两部分。
ActiveModel
class Vehicle
include ActiveModel::Dirty
include ActiveModel::Validations
include ActiveModel::Observing
attr_accessor :state
define_attribute_methods [:state]
state_machine :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
after_transition any => :parked do |vehicle, transition|
vehicle.seatbelt = 'off'
end
around_transition :benchmark
event :ignite do
transition :parked => :idling
end
state :first_gear, :second_gear do
validates_presence_of :seatbelt_on
end
end
def put_on_seatbelt
...
end
def benchmark
...
yield
...
end
end
class VehicleObserver < ActiveModel::Observer
# Callback for :ignite event *before* the transition is performed
def before_ignite(vehicle, transition)
# log message
end
# Generic transition callback *after* the transition is performed
def after_transition(vehicle, transition)
Audit.log(vehicle, transition)
end
# Generic callback after the transition fails to perform
def after_failure_to_transition(vehicle, transition)
Audit.error(vehicle, transition)
end
end
ActiveRecord
class Vehicle < ActiveRecord::Base
state_machine :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
after_transition any => :parked do |vehicle, transition|
vehicle.seatbelt = 'off'
end
around_transition :benchmark
event :ignite do
transition :parked => :idling
end
state :first_gear, :second_gear do
validates_presence_of :seatbelt_on
end
end
def put_on_seatbelt
...
end
def benchmark
...
yield
...
end
end
class VehicleObserver < ActiveRecord::Observer
# Callback for :ignite event *before* the transition is performed
def before_ignite(vehicle, transition)
# log message
end
# Generic transition callback *after* the transition is performed
def after_transition(vehicle, transition)
Audit.log(vehicle, transition)
end
end
通过例子来学习 ＝》
Class definition:
class Vehicle
attr_accessor :seatbelt_on, :time_used, :auto_shop_busy
state_machine :state, :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
after_transition :on => :crash, :do => :tow
after_transition :on => :repair, :do => :fix
after_transition any => :parked do |vehicle, transition|
vehicle.seatbelt_on = false
end
after_failure :on => :ignite, :do => :log_start_failure
around_transition do |vehicle, transition, block|
start = Time.now
block.call
vehicle.time_used += Time.now - start
end
event :park do
transition [:idling, :first_gear] => :parked
end
event :ignite do
transition :stalled => same, :parked => :idling
end
event :idle do
transition :first_gear => :idling
end
event :shift_up do
transition :idling => :first_gear, :first_gear => :second_gear, :second_gear => :third_gear
end
event :shift_down do
transition :third_gear => :second_gear, :second_gear => :first_gear
end
event :crash do
transition all - [:parked, :stalled] => :stalled, :if => lambda {|vehicle| !vehicle.passed_inspection?}
end
event :repair do
# The first transition that matches the state and passes its conditions
# will be used
transition :stalled => :parked, :unless => :auto_shop_busy
transition :stalled => same
end
state :parked do
def speed
0
end
end
state :idling, :first_gear do
def speed
10
end
end
state all - [:parked, :stalled, :idling] do
def moving?
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
上面例子中包含了很多东西，有的您可能用不到。具体点包括：
Initial states
Namespaced states
Transition callbacks
Conditional transitions
State-driven instance behavior
Customized state values
Parallel events
Path analysis
现在，您可以如下面这么用:
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 # => #<StateMachine::Transition attribute=:state event=:ignite from="parked" from_name=:parked to="idling" to_name=:idling>
vehicle.state_events # => [:ignite]
vehicle.state_transitions # => [#<StateMachine::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! # => StateMachine::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) # => StateMachine::InvalidTransition: 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 # => [[#<StateMachine::Transition ...], [#<StateMachine::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) # => [[
# #<StateMachine::Transition attribute=:state event=:ignite from="parked" ...>,
# #<StateMachine::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 StateMachine::MacroMethods#state_machine):
# vehicle.state = :parked
用于 Ruby on Rails
- 安装 gem
# In Gemfile
...
gem 'state_machine'
gem 'ruby-graphviz', :require => 'graphviz' # 可选: only required for graphing
然后 bundle install
- 创建 一个 model
和平常一样(Vehiche 这里仅用于举例):
$ rails generate model Vehicle state:string
$ rake db:migrate
- 配置 state machine
添加 state 到你的 model. 本例中为, app/models/vehicle.rb:
class Vehicle < ActiveRecord::Base
state_machine :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
...
end
end
- 跑 Rake tasks
rake state_machine:draw CLASS=Vehicle