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.

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.

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.

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

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]>

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

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

Defining transitions

The options for a new transition uses the Hash syntax to map beginning states to ending states. For example,

  transition :parked => :idling, :idling => :first_gear

In this case, when the event is fired, this transition will cause the state to be idling if it‘s current state is parked or first_gear if it‘s current state is idling.

To help define these implicit transitions, a set of helpers are available for slightly more complex matching:

  • all - Matches every state in the machine
  • all - [:parked, :idling, …] - Matches every state except those specified
  • any - An alias for all (matches every state in the machine)
  • same - Matches the same state being transitioned from

See StateMachine::MatcherHelpers for more information.

Examples:

  transition all => nil                               # Transitions to nil regardless of the current state
  transition all => :idling                           # Transitions to :idling regardless of the current state
  transition all - [:idling, :first_gear] => :idling  # Transitions every state but :idling and :first_gear to :idling
  transition nil => :idling                           # Transitions to :idling from the nil state
  transition :parked => :idling                       # Transitions to :idling if :parked
  transition [:parked, :stalled] => :idling           # Transitions to :idling if :parked or :stalled

  transition :parked => same                          # Loops :parked back to :parked
  transition [:parked, :stalled] => same              # Loops either :parked or :stalled back to the same state
  transition all - :parked => same                    # Loops every state but :parked back to the same state

  # Transitions to :idling if :parked, :first_gear if :idling, or :second_gear if :first_gear
  transition :parked => :idling, :idling => :first_gear, :first_gear => :second_gear

Verbose transitions

Transitions can also be defined use an explicit set of deprecated configuration options:

  • :from - A state or array of states that can be transitioned from. If not specified, then the transition can occur for any state.
  • :to - The state that‘s being transitioned to. If not specified, then the transition will simply loop back (i.e. the state will not change).
  • :except_from - A state or array of states that cannot be transitioned from.

Examples:

  transition :to => nil
  transition :to => :idling
  transition :except_from => [:idling, :first_gear], :to => :idling
  transition :from => nil, :to => :idling
  transition :from => [:parked, :stalled], :to => :idling

  transition :from => :parked
  transition :from => [:parked, :stalled]
  transition :except_from => :parked

Notice that the above examples are the verbose equivalent of the examples described initially.

Conditions

In addition to the state requirements for each transition, a condition can also be defined to help determine whether that transition is available. These options will work on both the normal and verbose syntax.

Configuration options:

  • :if - A method, proc or string to call to determine if the transition should occur (e.g. :if => :moving?, or :if => lambda {|vehicle| vehicle.speed > 60}). The condition should return or evaluate to true or false.
  • :unless - A method, proc or string to call to determine if the transition should not occur (e.g. :unless => :stopped?, or :unless => lambda {|vehicle| vehicle.speed <= 60}). The condition should return or evaluate to true or false.

Examples:

  transition :parked => :idling, :if => :moving?
  transition :parked => :idling, :unless => :stopped?
  transition :idling => :first_gear, :first_gear => :second_gear, :if => :seatbelt_on?

  transition :from => :parked, :to => :idling, :if => :moving?
  transition :from => :parked, :to => :idling, :unless => :stopped?

Order of operations

Transitions are evaluated in the order in which they‘re defined. As a result, if more than one transition applies to a given object, then the first transition that matches will be performed.

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.

Protected Instance methods

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

[Validate]