Class StateMachine::StateContext
In: lib/state_machine/state_context.rb
Parent: Module

Represents a module which will get evaluated within the context of a state.

Class-level methods are proxied to the owner class, injecting a custom :if condition along with method. This assumes that the method has support for a set of configuration options, including :if. This condition will check that the object‘s state matches this context‘s state.

Instance-level methods are used to define state-driven behavior on the state‘s owner class.

Examples

  class Vehicle
    class << self
      attr_accessor :validations

      def validate(options, &block)
        validations << options
      end
    end

    self.validations = []
    attr_accessor :state, :simulate

    def moving?
      self.class.validations.all? {|validation| validation[:if].call(self)}
    end
  end

In the above class, a simple set of validation behaviors have been defined. Each validation consists of a configuration like so: 

  Vehicle.validate :unless => :simulate
  Vehicle.validate :if => lambda {|vehicle| ...}

In order to scope validations to a particular state context, the class-level validate method can be invoked like so: 

  machine = StateMachine::Machine.new(Vehicle)
  context = StateMachine::StateContext.new(machine.state(:first_gear))
  context.validate(:unless => :simulate)

  vehicle = Vehicle.new     # => #<Vehicle:0xb7ce491c @simulate=nil, @state=nil>
  vehicle.moving?           # => false

  vehicle.state = 'first_gear'
  vehicle.moving?           # => true

  vehicle.simulate = true
  vehicle.moving?           # => false

Methods

method_missing   new   transition  

Included Modules

Assertions EvalHelpers

Attributes

machine  [R]  The state machine for which this context‘s state is defined
state  [R]  The state that must be present in an object for this context to be active

Public Class methods

new(state)

Creates a new context for the given state

[Source]

    # File lib/state_machine/state_context.rb, line 66
66:     def initialize(state)
67:       @state = state
68:       @machine = state.machine
69:       
70:       state_name = state.name
71:       machine_name = machine.name
72:       @condition = lambda {|object| object.class.state_machine(machine_name).states.matches?(object, state_name)}
73:     end

Public Instance methods

method_missing(*args, &block)

Hooks in condition-merging to methods that don‘t exist in this module

[Source]

     # File lib/state_machine/state_context.rb, line 100
100:     def method_missing(*args, &block)
101:       # Get the configuration
102:       if args.last.is_a?(Hash)
103:         options = args.last
104:       else
105:         args << options = {}
106:       end
107:       
108:       # Get any existing condition that may need to be merged
109:       if_condition = options.delete(:if)
110:       unless_condition = options.delete(:unless)
111:       
112:       # Provide scope access to configuration in case the block is evaluated
113:       # within the object instance
114:       proxy = self
115:       proxy_condition = @condition
116:       
117:       # Replace the configuration condition with the one configured for this
118:       # proxy, merging together any existing conditions
119:       options[:if] = lambda do |*args|
120:         # Block may be executed within the context of the actual object, so
121:         # it'll either be the first argument or the executing context
122:         object = args.first || self
123:         
124:         proxy.evaluate_method(object, proxy_condition) &&
125:         Array(if_condition).all? {|condition| proxy.evaluate_method(object, condition)} &&
126:         !Array(unless_condition).any? {|condition| proxy.evaluate_method(object, condition)}
127:       end
128:       
129:       # Evaluate the method on the owner class with the condition proxied
130:       # through
131:       machine.owner_class.send(*args, &block)
132:     end
transition(options)

Creates a new transition that determines what to change the current state to when an event fires from this state.

Since this transition is being defined within a state context, you do not need to specify the :from option for the transition. For example: 

  state_machine do
    state :parked do
      transition :to => :idling, :on => [:ignite, :shift_up]                          # Transitions to :idling
      transition :from => [:idling, :parked], :on => :park, :unless => :seatbelt_on?  # Transitions to :parked if seatbelt is off
    end
  end

See StateMachine::Machine#transition for a description of the possible configurations for defining transitions.

[Source]

    # File lib/state_machine/state_context.rb, line 91
91:     def transition(options)
92:       assert_valid_keys(options, :from, :to, :on, :if, :unless)
93:       raise ArgumentError, 'Must specify :on event' unless options[:on]
94:       raise ArgumentError, 'Must specify either :to or :from state' unless !options[:to] ^ !options[:from]
95:       
96:       machine.transition(options.merge(options[:to] ? {:from => state.name} : {:to => state.name}))
97:     end

[Validate]