Class StateMachine::Event
In: lib/state_machine/event.rb
Parent: Object

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.

Methods

Included Modules

Assertions MatcherHelpers

Attributes

branches  [R]  The list of branches that determine what state this event transitions objects to when fired
human_name  [W]  The human-readable name for the event
known_states  [R]  A list of all of the states known to this event using the configured branches/transitions as the source
machine  [RW]  The state machine for which this event is defined
name  [R]  The name of the event
qualified_name  [R]  The fully-qualified name of the event, scoped by the machine‘s namespace

Public Instance methods

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.

[Source]

     # File lib/state_machine/event.rb, line 130
130:     def can_fire?(object, requirements = {})
131:       !transition_for(object, requirements).nil?
132:     end

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

[Source]

    # File lib/state_machine/event.rb, line 90
90:     def context(&block)
91:       instance_eval(&block)
92:     end

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.

[Source]

     # File lib/state_machine/event.rb, line 202
202:     def draw(graph)
203:       valid_states = machine.states.by_priority.map {|state| state.name}
204:       branches.collect {|branch| branch.draw(graph, name, valid_states)}.flatten
205:     end

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.

[Source]

     # File lib/state_machine/event.rb, line 168
168:     def fire(object, *args)
169:       machine.reset(object)
170:       
171:       if transition = transition_for(object)
172:         transition.perform(*args)
173:       else
174:         on_failure(object)
175:         false
176:       end
177:     end

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

[Source]

    # File lib/state_machine/event.rb, line 84
84:     def human_name(klass = @machine.owner_class)
85:       @human_name.is_a?(Proc) ? @human_name.call(self, klass) : @human_name
86:     end

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]>

[Source]

     # File lib/state_machine/event.rb, line 214
214:     def inspect
215:       transitions = branches.map do |branch|
216:         branch.state_requirements.map do |state_requirement|
217:           "#{state_requirement[:from].description} => #{state_requirement[:to].description}"
218:         end * ', '
219:       end
220:       
221:       "#<#{self.class} name=#{name.inspect} transitions=[#{transitions * ', '}]>"
222:     end

Converts the name of this event to a string

[Source]

    # File lib/state_machine/event.rb, line 70
70:     def name_to_s
71:       name.to_s
72:     end

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

[Source]

     # File lib/state_machine/event.rb, line 181
181:     def on_failure(object)
182:       state = machine.states.match!(object)
183:       machine.invalidate(object, :state, :invalid_transition, [[:event, human_name(object.class)], [:state, state.human_name(object.class)]])
184:       
185:       Transition.new(object, machine, name, state.name, state.name).run_callbacks(:before => false)
186:     end

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.

[Source]

     # File lib/state_machine/event.rb, line 192
192:     def reset
193:       @branches = []
194:       @known_states = []
195:     end

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.

[Source]

     # File lib/state_machine/event.rb, line 110
110:     def transition(options)
111:       raise ArgumentError, 'Must specify as least one transition requirement' if options.empty?
112:       
113:       # Only a certain subset of explicit options are allowed for transition
114:       # requirements
115:       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?
116:       
117:       branches << branch = Branch.new(options.merge(:on => name))
118:       @known_states |= branch.known_states
119:       branch
120:     end

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.

[Source]

     # File lib/state_machine/event.rb, line 144
144:     def transition_for(object, requirements = {})
145:       assert_valid_keys(requirements, :from, :to, :guard)
146:       requirements[:from] = machine.states.match!(object).name unless custom_from_state = requirements.include?(:from)
147:       
148:       branches.each do |branch|
149:         if match = branch.match(object, requirements)
150:           # Branch allows for the transition to occur
151:           from = requirements[:from]
152:           to = match[:to].values.empty? ? from : match[:to].values.first
153:           
154:           return Transition.new(object, machine, name, from, to, !custom_from_state)
155:         end
156:       end
157:       
158:       # No transition matched
159:       nil
160:     end

Protected Instance methods

Add the various instance methods that can transition the object using the current event

[Source]

     # File lib/state_machine/event.rb, line 227
227:       def add_actions
228:         # Checks whether the event can be fired on the current object
229:         machine.define_helper(:instance, "can_#{qualified_name}?") do |machine, object, *args|
230:           machine.event(name).can_fire?(object, *args)
231:         end
232:         
233:         # Gets the next transition that would be performed if the event were
234:         # fired now
235:         machine.define_helper(:instance, "#{qualified_name}_transition") do |machine, object, *args|
236:           machine.event(name).transition_for(object, *args)
237:         end
238:         
239:         # Fires the event
240:         machine.define_helper(:instance, qualified_name) do |machine, object, *args|
241:           machine.event(name).fire(object, *args)
242:         end
243:         
244:         # Fires the event, raising an exception if it fails
245:         machine.define_helper(:instance, "#{qualified_name}!") do |machine, object, *args|
246:           object.send(qualified_name, *args) || raise(StateMachine::InvalidTransition.new(object, machine, name))
247:         end
248:       end

[Validate]