class StateMachine::Event
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.
Attributes
The list of branches that determine what state this event transitions objects to when fired
The human-readable name for the event
A list of all of the states known to this event using the configured branches/transitions as the source
The state machine for which this event is defined
The name of the event
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.
# File lib/state_machine/event.rb, line 125 def can_fire?(object, requirements = {}) !transition_for(object, requirements).nil? end
Evaluates the given block within the context of this event. This simply provides a DSL-like syntax for defining transitions.
# File lib/state_machine/event.rb, line 85 def context(&block) instance_eval(&block) 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.
Configuration options:
-
:human_name
- Whether to use the event's human name for the node's label that gets drawn on the graph
# File lib/state_machine/event.rb, line 204 def draw(graph, options = {}) valid_states = machine.states.by_priority.map {|state| state.name} branches.each do |branch| branch.draw(graph, options[:human_name] ? human_name : name, valid_states) end true 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.
# File lib/state_machine/event.rb, line 168 def fire(object, *args) machine.reset(object) if transition = transition_for(object) transition.perform(*args) else on_failure(object) false end end
Transforms the event name into a more human-readable format, such as “turn on” instead of “turn_on”
# 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
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]>
# File lib/state_machine/event.rb, line 220 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
Marks the object as invalid and runs any failure callbacks associated with this event. This should get called anytime this event fails to transition.
# File lib/state_machine/event.rb, line 181 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
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.
# File lib/state_machine/event.rb, line 192 def reset @branches = [] @known_states = [] 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.
# 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, :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
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.
# 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 = if match[:to].is_a?(LoopbackMatcher) from else values = requirements.include?(:to) ? [requirements[:to]].flatten : [from] | machine.states.keys(: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
Protected Instance Methods
Add the various instance methods that can transition the object using the current event
# File lib/state_machine/event.rb, line 233 def add_actions # Checks whether the event can be fired on the current object machine.define_helper(:instance, "can_#{qualified_name}?") do |machine, object, *args| machine.event(name).can_fire?(object, *args) end # Gets the next transition that would be performed if the event were # fired now machine.define_helper(:instance, "#{qualified_name}_transition") do |machine, object, *args| machine.event(name).transition_for(object, *args) end # Fires the event machine.define_helper(:instance, qualified_name) do |machine, object, *args| machine.event(name).fire(object, *args) end # Fires the event, raising an exception if it fails machine.define_helper(:instance, "#{qualified_name}!") do |machine, object, *args| object.send(qualified_name, *args) || raise(StateMachine::InvalidTransition.new(object, machine, name)) end end