Class: StateMachines::Event

Inherits:
Object
  • Object
show all
Includes:
MatcherHelpers
Defined in:
lib/state_machines/event.rb

Overview

An event defines an action that transitions an attribute from one state to another. The state that an attribute is transitioned to depends on the branches configured for the event.

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from MatcherHelpers

#all, #same

Constructor Details

#initialize(machine, name, options = {}) ⇒ Event

Creates a new event within the context of the given machine

Configuration options:

  • :human_name - The human-readable version of this event's name


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# File 'lib/state_machines/event.rb', line 33

def initialize(machine, name, options = {}) #:nodoc:
  options.assert_valid_keys(:human_name)

  @machine = machine
  @name = name
  @qualified_name = machine.namespace ? :"#{name}_#{machine.namespace}" : name
  @human_name = options[:human_name] || @name.to_s.tr('_', ' ')
  reset

  # Output a warning if another event has a conflicting qualified name
  if conflict = machine.owner_class.state_machines.detect { |_other_name, other_machine| other_machine != @machine && other_machine.events[qualified_name, :qualified_name] }
    _name, other_machine = conflict
    warn "Event #{qualified_name.inspect} for #{machine.name.inspect} is already defined in #{other_machine.name.inspect}"
  else
    add_actions
  end
end

Instance Attribute Details

#branches ⇒ Object (readonly)

The list of branches that determine what state this event transitions objects to when fired


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# File 'lib/state_machines/event.rb', line 23

def branches
  @branches
end

#human_name(klass = @machine.owner_class) ⇒ Object

Transforms the event name into a more human-readable format, such as “turn on” instead of “turn_on”


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# File 'lib/state_machines/event.rb', line 61

def human_name(klass = @machine.owner_class)
  @human_name.is_a?(Proc) ? @human_name.call(self, klass) : @human_name
end

#known_states ⇒ Object (readonly)

A list of all of the states known to this event using the configured branches/transitions as the source


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# File 'lib/state_machines/event.rb', line 27

def known_states
  @known_states
end

#machine ⇒ Object

The state machine for which this event is defined


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# File 'lib/state_machines/event.rb', line 10

def machine
  @machine
end

#name ⇒ Object (readonly)

The name of the event


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# File 'lib/state_machines/event.rb', line 13

def name
  @name
end

#qualified_name ⇒ Object (readonly)

The fully-qualified name of the event, scoped by the machine's namespace


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# File 'lib/state_machines/event.rb', line 16

def qualified_name
  @qualified_name
end

Instance Method Details

#can_fire?(object, requirements = {}) ⇒ Boolean

Determines whether any transitions can be performed for this event based on the current state of the given object.

If the event can't be fired, then this will return false, otherwise true.

Note that this will not take the object context into account. Although a transition may be possible based on the state machine definition, object-specific behaviors (like validations) may prevent it from firing.

Returns:

  • (Boolean) 

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# File 'lib/state_machines/event.rb', line 107

def can_fire?(object, requirements = {})
  !transition_for(object, requirements).nil?
end

#context(&block) ⇒ Object

Evaluates the given block within the context of this event. This simply provides a DSL-like syntax for defining transitions.


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# File 'lib/state_machines/event.rb', line 67

def context(&block)
  instance_eval(&block)
end

#draw(graph, options = {}) ⇒ Object 


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# File 'lib/state_machines/event.rb', line 183

def draw(graph, options = {})
  fail NotImplementedError
end

#fire(object, *args) ⇒ Object

Attempts to perform the next available transition on the given object. If no transitions can be made, then this will return false, otherwise true.

Any additional arguments are passed to the StateMachines::Transition#perform instance method.


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# File 'lib/state_machines/event.rb', line 151

def fire(object, *args)
  machine.reset(object)

  if transition = transition_for(object)
    transition.perform(*args)
  else
    on_failure(object, *args)
    false
  end
end

#initialize_copy(orig) ⇒ Object

Creates a copy of this event in addition to the list of associated branches to prevent conflicts across events within a class hierarchy.


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# File 'lib/state_machines/event.rb', line 53

def initialize_copy(orig) #:nodoc:
  super
  @branches = @branches.dup
  @known_states = @known_states.dup
end

#inspect ⇒ Object

Generates a nicely formatted description of this event's contents.

For example,

event = StateMachines::Event.new(machine, :park)
event.transition all - :idling => :parked, :idling => same
event   # => #<StateMachines::Event name=:park transitions=[all - :idling => :parked, :idling => same]>


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# File 'lib/state_machines/event.rb', line 194

def inspect
  transitions = branches.map do |branch|
    branch.state_requirements.map do |state_requirement|
      "#{state_requirement[:from].description} => #{state_requirement[:to].description}"
    end * ', '
  end

  "#<#{self.class} name=#{name.inspect} transitions=[#{transitions * ', '}]>"
end

#on_failure(object, *args) ⇒ Object

Marks the object as invalid and runs any failure callbacks associated with this event. This should get called anytime this event fails to transition.


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# File 'lib/state_machines/event.rb', line 164

def on_failure(object, *args)
  state = machine.states.match!(object)
  machine.invalidate(object, :state, :invalid_transition, [[:event, human_name(object.class)], [:state, state.human_name(object.class)]])

  transition = Transition.new(object, machine, name, state.name, state.name)
  transition.args = args if args.any?
  transition.run_callbacks(:before => false)
end

#reset ⇒ Object

Resets back to the initial state of the event, with no branches / known states associated. This allows you to redefine an event in situations where you either are re-using an existing state machine implementation or are subclassing machines.


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# File 'lib/state_machines/event.rb', line 177

def reset
  @branches = []
  @known_states = []
end

#transition(options) ⇒ Object

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

Since this transition is being defined within an event context, you do not need to specify the :on option for the transition. For example:

state_machine do
  event :ignite do
    transition :parked => :idling, :idling => same, :if => :seatbelt_on? # Transitions to :idling if seatbelt is on
    transition all => :parked, :unless => :seatbelt_on?                  # Transitions to :parked if seatbelt is off
  end
end

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

Raises:

  • (ArgumentError) 

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# File 'lib/state_machines/event.rb', line 87

def transition(options)
  raise ArgumentError, 'Must specify as least one transition requirement' if options.empty?

  # Only a certain subset of explicit options are allowed for transition
  # requirements
  options.assert_valid_keys(:from, :to, :except_from, :except_to, :if, :unless) if (options.keys - [:from, :to, :on, :except_from, :except_to, :except_on, :if, :unless]).empty?

  branches << branch = Branch.new(options.merge(:on => name))
  @known_states |= branch.known_states
  branch
end

#transition_for(object, requirements = {}) ⇒ Object

Finds and builds the next transition that can be performed on the given object. If no transitions can be made, then this will return nil.

Valid requirement options:

  • :from - One or more states being transitioned from. If none are specified, then this will be the object's current state.

  • :to - One or more states being transitioned to. If none are specified, then this will match any to state.

  • :guard - Whether to guard transitions with the if/unless conditionals defined for each one. Default is true.


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# File 'lib/state_machines/event.rb', line 121

def transition_for(object, requirements = {})
  requirements.assert_valid_keys(:from, :to, :guard)
  requirements[:from] = machine.states.match!(object).name unless custom_from_state = requirements.include?(:from)

  branches.each do |branch|
    if match = branch.match(object, requirements)
      # Branch allows for the transition to occur
      from = requirements[:from]
      to = if match[:to].is_a?(LoopbackMatcher)
             from
           else
             values = requirements.include?(:to) ? [requirements[:to]].flatten : [from] | machine.states.map { |state| state.name }

             match[:to].filter(values).first
           end

      return Transition.new(object, machine, name, from, to, !custom_from_state)
    end
  end

  # No transition matched
  nil
end