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 125
125:     def can_fire?(object, requirements = {})
126:       !transition_for(object, requirements).nil?
127:     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 85
85:     def context(&block)
86:       instance_eval(&block)
87:     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 197
197:     def draw(graph)
198:       valid_states = machine.states.by_priority.map {|state| state.name}
199:       branches.collect {|branch| branch.draw(graph, name, valid_states)}.flatten
200:     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 163
163:     def fire(object, *args)
164:       machine.reset(object)
165:       
166:       if transition = transition_for(object)
167:         transition.perform(*args)
168:       else
169:         on_failure(object)
170:         false
171:       end
172:     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 79
79:     def human_name(klass = @machine.owner_class)
80:       @human_name.is_a?(Proc) ? @human_name.call(self, klass) : @human_name
81:     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 209
209:     def inspect
210:       transitions = branches.map do |branch|
211:         branch.state_requirements.map do |state_requirement|
212:           "#{state_requirement[:from].description} => #{state_requirement[:to].description}"
213:         end * ', '
214:       end
215:       
216:       "#<#{self.class} name=#{name.inspect} transitions=[#{transitions * ', '}]>"
217:     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 176
176:     def on_failure(object)
177:       state = machine.states.match!(object)
178:       machine.invalidate(object, :state, :invalid_transition, [[:event, human_name(object.class)], [:state, state.human_name(object.class)]])
179:       
180:       Transition.new(object, machine, name, state.name, state.name).run_callbacks(:before => false)
181:     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 187
187:     def reset
188:       @branches = []
189:       @known_states = []
190:     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 105
105:     def transition(options)
106:       raise ArgumentError, 'Must specify as least one transition requirement' if options.empty?
107:       
108:       # Only a certain subset of explicit options are allowed for transition
109:       # requirements
110:       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?
111:       
112:       branches << branch = Branch.new(options.merge(:on => name))
113:       @known_states |= branch.known_states
114:       branch
115:     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 139
139:     def transition_for(object, requirements = {})
140:       assert_valid_keys(requirements, :from, :to, :guard)
141:       requirements[:from] = machine.states.match!(object).name unless custom_from_state = requirements.include?(:from)
142:       
143:       branches.each do |branch|
144:         if match = branch.match(object, requirements)
145:           # Branch allows for the transition to occur
146:           from = requirements[:from]
147:           to = match[:to].values.empty? ? from : match[:to].values.first
148:           
149:           return Transition.new(object, machine, name, from, to, !custom_from_state)
150:         end
151:       end
152:       
153:       # No transition matched
154:       nil
155:     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 222
222:       def add_actions
223:         # Checks whether the event can be fired on the current object
224:         machine.define_helper(:instance, "can_#{qualified_name}?") do |machine, object, *args|
225:           machine.event(name).can_fire?(object, *args)
226:         end
227:         
228:         # Gets the next transition that would be performed if the event were
229:         # fired now
230:         machine.define_helper(:instance, "#{qualified_name}_transition") do |machine, object, *args|
231:           machine.event(name).transition_for(object, *args)
232:         end
233:         
234:         # Fires the event
235:         machine.define_helper(:instance, qualified_name) do |machine, object, *args|
236:           machine.event(name).fire(object, *args)
237:         end
238:         
239:         # Fires the event, raising an exception if it fails
240:         machine.define_helper(:instance, "#{qualified_name}!") do |machine, object, *args|
241:           object.send(qualified_name, *args) || raise(StateMachine::InvalidTransition.new(object, machine, name))
242:         end
243:       end

[Validate]