Class: StateMachine::Event

Inherits:
Object
  • Object
show all
Includes:
Assertions, MatcherHelpers
Defined in:
lib/state_machine/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

Methods included from Assertions

#assert_exclusive_keys, #assert_valid_keys

Constructor Details

- (Event) initialize(machine, name, options = {})

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_machine/event.rb', line 51

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

- (Object) branches (readonly)

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



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# File 'lib/state_machine/event.rb', line 41

def branches
  @branches
end

- (Object) human_name(klass = @machine.owner_class)

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_machine/event.rb', line 79

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

- (Object) known_states (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_machine/event.rb', line 45

def known_states
  @known_states
end

- (Object) machine

The state machine for which this event is defined



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# File 'lib/state_machine/event.rb', line 28

def machine
  @machine
end

- (Object) name (readonly)

The name of the event



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# File 'lib/state_machine/event.rb', line 31

def name
  @name
end

- (Object) qualified_name (readonly)

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



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# File 'lib/state_machine/event.rb', line 34

def qualified_name
  @qualified_name
end

Instance Method Details

- (Boolean) can_fire?(object, requirements = {})

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_machine/event.rb', line 125

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

- (Object) context(&block)

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_machine/event.rb', line 85

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

- (Object) draw(graph)

Draws a representation of this event on the given graph. This will create 1 or more edges on the graph for each branch (i.e. transition) configured.

A collection of the generated edges will be returned.



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# File 'lib/state_machine/event.rb', line 197

def draw(graph)
  valid_states = machine.states.by_priority.map {|state| state.name}
  branches.collect {|branch| branch.draw(graph, name, valid_states)}.flatten
end

- (Object) fire(object, *args)

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 StateMachine::Transition#perform instance method.



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# File 'lib/state_machine/event.rb', line 163

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

- (Object) initialize_copy(orig)

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_machine/event.rb', line 71

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

- (Object) inspect

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

For example,

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


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# File 'lib/state_machine/event.rb', line 209

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

- (Object) on_failure(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_machine/event.rb', line 176

def on_failure(object)
  state = machine.states.match!(object)
  machine.invalidate(object, :state, :invalid_transition, [[:event, human_name(object.class)], [:state, state.human_name(object.class)]])
  
  Transition.new(object, machine, name, state.name, state.name).run_callbacks(:before => false)
end

- (Object) reset

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_machine/event.rb', line 187

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

- (Object) transition(options)

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

Raises:

  • (ArgumentError)


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# File 'lib/state_machine/event.rb', line 105

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
  assert_valid_keys(options, :from, :to, :except_from, :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

- (Object) transition_for(object, requirements = {})

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_machine/event.rb', line 139

def transition_for(object, requirements = {})
  assert_valid_keys(requirements, :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 = match[:to].values.empty? ? from : match[:to].values.first
      
      return Transition.new(object, machine, name, from, to, !custom_from_state)
    end
  end
  
  # No transition matched
  nil
end