class StateMachine::Transition

A transition represents a state change for a specific attribute.

Transitions consist of:

Attributes

args[RW]

The arguments passed in to the event that triggered the transition (does not include the run_action boolean argument if specified)

from[R]

The original state value before the transition

machine[R]

The state machine for which this transition is defined

object[R]

The object being transitioned

result[R]

The result of invoking the action associated with the machine

to[R]

The new state value after the transition

transient[W]

Whether the transition is only existing temporarily for the object

Public Class Methods

pause_supported?() click to toggle source

Determines whether the curreny ruby implementation supports pausing and resuming transitions

# File lib/state_machine/transition.rb, line 89
def self.pause_supported?
  !defined?(RUBY_ENGINE) || %w(ruby maglev).include?(RUBY_ENGINE)
end

Public Instance Methods

==(other) click to toggle source

Determines equality of transitions by testing whether the object, states, and event involved in the transition are equal

# File lib/state_machine/transition.rb, line 320
def ==(other)
  other.instance_of?(self.class) &&
  other.object == object &&
  other.machine == machine &&
  other.from_name == from_name &&
  other.to_name == to_name &&
  other.event == event
end
action() click to toggle source

The action that will be run when this transition is performed

# File lib/state_machine/transition.rb, line 116
def action
  machine.action
end
attribute() click to toggle source

The attribute which this transition's machine is defined for

# File lib/state_machine/transition.rb, line 111
def attribute
  machine.attribute
end
attributes() click to toggle source

A hash of all the core attributes defined for this transition with their names as keys and values of the attributes as values.

Example

machine = StateMachine.new(Vehicle)
transition = StateMachine::Transition.new(Vehicle.new, machine, :ignite, :parked, :idling)
transition.attributes   # => {:object => #<Vehicle:0xb7d60ea4>, :attribute => :state, :event => :ignite, :from => 'parked', :to => 'idling'}
# File lib/state_machine/transition.rb, line 192
def attributes
  @attributes ||= {:object => object, :attribute => attribute, :event => event, :from => from, :to => to}
end
event() click to toggle source

The event that triggered the transition

# File lib/state_machine/transition.rb, line 121
def event
  @event.name
end
from_name() click to toggle source

The state name before the transition

# File lib/state_machine/transition.rb, line 136
def from_name
  @from_state.name
end
human_event() click to toggle source

The human-readable name of the event that triggered the transition

# File lib/state_machine/transition.rb, line 131
def human_event
  @event.human_name(@object.class)
end
human_from_name() click to toggle source

The human-readable state name before the transition

# File lib/state_machine/transition.rb, line 146
def human_from_name
  @from_state.human_name(@object.class)
end
human_to_name() click to toggle source

The new human-readable state name after the transition

# File lib/state_machine/transition.rb, line 161
def human_to_name
  @to_state.human_name(@object.class)
end
inspect() click to toggle source

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

For example,

transition = StateMachine::Transition.new(object, machine, :ignite, :parked, :idling)
transition   # => #<StateMachine::Transition attribute=:state event=:ignite from="parked" from_name=:parked to="idling" to_name=:idling>
# File lib/state_machine/transition.rb, line 335
def inspect
  "#<#{self.class} #{%w(attribute event from from_name to to_name).map {|attr| "#{attr}=#{send(attr).inspect}"} * ' '}>"
end
loopback?() click to toggle source

Does this transition represent a loopback (i.e. the from and to state are the same)

Example

machine = StateMachine.new(Vehicle)
StateMachine::Transition.new(Vehicle.new, machine, :park, :parked, :parked).loopback?   # => true
StateMachine::Transition.new(Vehicle.new, machine, :park, :idling, :parked).loopback?   # => false
# File lib/state_machine/transition.rb, line 173
def loopback?
  from_name == to_name
end
perform(*args) click to toggle source

Runs the actual transition and any before/after callbacks associated with the transition. The action associated with the transition/machine can be skipped by passing in false.

Examples

class Vehicle
  state_machine :action => :save do
    ...
  end
end

vehicle = Vehicle.new
transition = StateMachine::Transition.new(vehicle, machine, :ignite, :parked, :idling)
transition.perform                  # => Runs the +save+ action after setting the state attribute
transition.perform(false)           # => Only sets the state attribute
transition.perform(Time.now)        # => Passes in additional arguments and runs the +save+ action
transition.perform(Time.now, false) # => Passes in additional arguments and only sets the state attribute
# File lib/state_machine/transition.rb, line 214
def perform(*args)
  run_action = [true, false].include?(args.last) ? args.pop : true
  self.args = args
  
  # Run the transition
  !!TransitionCollection.new([self], :actions => run_action).perform
end
persist() click to toggle source

Transitions the current value of the state to that specified by the transition. Once the state is persisted, it cannot be persisted again until this transition is reset.

Example

class Vehicle
  state_machine do
    event :ignite do
      transition :parked => :idling
    end
  end
end

vehicle = Vehicle.new
transition = StateMachine::Transition.new(vehicle, Vehicle.state_machine, :ignite, :parked, :idling)
transition.persist

vehicle.state   # => 'idling'
# File lib/state_machine/transition.rb, line 275
def persist
  unless @persisted
    machine.write(object, :state, to)
    @persisted = true
  end
end
qualified_event() click to toggle source

The fully-qualified name of the event that triggered the transition

# File lib/state_machine/transition.rb, line 126
def qualified_event
  @event.qualified_name
end
qualified_from_name() click to toggle source

The fully-qualified state name before the transition

# File lib/state_machine/transition.rb, line 141
def qualified_from_name
  @from_state.qualified_name
end
qualified_to_name() click to toggle source

The new fully-qualified state name after the transition

# File lib/state_machine/transition.rb, line 156
def qualified_to_name
  @to_state.qualified_name
end
reset() click to toggle source

Resets any tracking of which callbacks have already been run and whether the state has already been persisted

# File lib/state_machine/transition.rb, line 313
def reset
  @before_run = @persisted = @after_run = false
  @paused_block = nil
end
rollback() click to toggle source

Rolls back changes made to the object's state via this transition. This will revert the state back to the from value.

Example

class Vehicle
  state_machine :initial => :parked do
    event :ignite do
      transition :parked => :idling
    end
  end
end

vehicle = Vehicle.new     # => #<Vehicle:0xb7b7f568 @state="parked">
transition = StateMachine::Transition.new(vehicle, Vehicle.state_machine, :ignite, :parked, :idling)

# Persist the new state
vehicle.state             # => "parked"
transition.persist
vehicle.state             # => "idling"

# Roll back to the original state
transition.rollback
vehicle.state             # => "parked"
# File lib/state_machine/transition.rb, line 306
def rollback
  reset
  machine.write(object, :state, from)
end
run_callbacks(options = {}, &block) click to toggle source

Runs the before / after callbacks for this transition. If a block is provided, then it will be executed between the before and after callbacks.

Configuration options:

  • before - Whether to run before callbacks.

  • after - Whether to run after callbacks. If false, then any around callbacks will be paused until called again with after enabled. Default is true.

This will return true if all before callbacks gets executed. After callbacks will not have an effect on the result.

# File lib/state_machine/transition.rb, line 242
def run_callbacks(options = {}, &block)
  options = {:before => true, :after => true}.merge(options)
  @success = false
  
  halted = pausable { before(options[:after], &block) } if options[:before]
  
  # After callbacks are only run if:
  # * An around callback didn't halt after yielding
  # * They're enabled or the run didn't succeed
  after if !(@before_run && halted) && (options[:after] || !@success)
  
  @before_run
end
to_name() click to toggle source

The new state name after the transition

# File lib/state_machine/transition.rb, line 151
def to_name
  @to_state.name
end
transient?() click to toggle source

Is this transition existing for a short period only? If this is set, it indicates that the transition (or the event backing it) should not be written to the object if it fails.

# File lib/state_machine/transition.rb, line 180
def transient?
  @transient
end
within_transaction() { || ... } click to toggle source

Runs a block within a transaction for the object being transitioned. By default, transactions are a no-op unless otherwise defined by the machine's integration.

# File lib/state_machine/transition.rb, line 225
def within_transaction
  machine.within_transaction(object) do
    yield
  end
end

Private Instance Methods

after() click to toggle source

Runs the machine's after callbacks for this transition. Only callbacks that are configured to match the event, from state, and to state will be invoked.

Once the callbacks are run, they cannot be run again until this transition is reset.

Halting

If any callback throws a :halt exception, it will be caught and the callback chain will be automatically stopped. However, this exception will not bubble up to the caller since after callbacks should never halt the execution of a perform.

# File lib/state_machine/transition.rb, line 444
def after
  unless @after_run
    # First resume previously paused callbacks
    if resume
      catch(:halt) do
        type = @success ? :after : :failure
        machine.callbacks[type].each {|callback| callback.call(object, context, self)}
      end
    end
    
    @after_run = true
  end
end
before(complete = true, index = 0) { |: {}| ... } click to toggle source

Runs the machine's before callbacks for this transition. Only callbacks that are configured to match the event, from state, and to state will be invoked.

Once the callbacks are run, they cannot be run again until this transition is reset.

# File lib/state_machine/transition.rb, line 399
def before(complete = true, index = 0, &block)
  unless @before_run
    while callback = machine.callbacks[:before][index]
      index += 1
      
      if callback.type == :around
        # Around callback: need to handle recursively.  Execution only gets
        # paused if:
        # * The block fails and the callback doesn't run on failures OR
        # * The block succeeds, but after callbacks are disabled (in which
        #   case a continuation is stored for later execution)
        return if catch(:cancel) do
          callback.call(object, context, self) do
            before(complete, index, &block)
            
            pause if @success && !complete
            throw :cancel, true unless @success
          end
        end
      else
        # Normal before callback
        callback.call(object, context, self)
      end
    end
    
    @before_run = true
  end
  
  action = {:success => true}.merge(block_given? ? yield : {})
  @result, @success = action[:result], action[:success]
end
context() click to toggle source

Gets a hash of the context defining this unique transition (including event, from state, and to state).

Example

machine = StateMachine.new(Vehicle)
transition = StateMachine::Transition.new(Vehicle.new, machine, :ignite, :parked, :idling)
transition.context    # => {:on => :ignite, :from => :parked, :to => :idling}
# File lib/state_machine/transition.rb, line 466
def context
  @context ||= {:on => event, :from => from_name, :to => to_name}
end
pausable() { || ... } click to toggle source

Runs a block that may get paused. If the block doesn't pause, then execution will continue as normal. If the block gets paused, then it will take care of switching the execution context when it's resumed.

This will return true if the given block halts for a reason other than getting paused.

# File lib/state_machine/transition.rb, line 346
def pausable
  begin
    halted = !catch(:halt) { yield; true }
  rescue Exception => error
    raise unless @resume_block
  end
  
  if @resume_block
    @resume_block.call(halted, error)
  else
    halted
  end
end
pause() click to toggle source

Pauses the current callback execution. This should only occur within around callbacks when the remainder of the callback will be executed at a later point in time.

# File lib/state_machine/transition.rb, line 363
def pause
  raise ArgumentError, 'around_transition callbacks cannot be called in multiple execution contexts in java implementations of Ruby. Use before/after_transitions instead.' unless self.class.pause_supported?
  
  unless @resume_block
    require 'continuation' unless defined?(callcc)
    callcc do |block|
      @paused_block = block
      throw :halt, true
    end
  end
end
resume() click to toggle source

Resumes the execution of a previously paused callback execution. Once the paused callbacks complete, the current execution will continue.

# File lib/state_machine/transition.rb, line 377
def resume
  if @paused_block
    halted, error = callcc do |block|
      @resume_block = block
      @paused_block.call
    end
    
    @resume_block = @paused_block = nil
    
    raise error if error
    !halted
  else
    true
  end
end