state-machines/state_machine - Next state in transitions

Question

I'm using https://github.com/state-machines/state_machines for Rails for storing and doing work before and after a state change of an object.

What I'd like to do is have a single method which can be called in a before_transition for a given set of events, and for a given event, have the method called by the before_transition do something a bit differently.

For example, say the method is called log_state_change, something like:

def log_state_change
  case <???>
  when "successful"
    Rails.logger.info "Successful"
  when "failure"
    Rails.logger.info "Failure"
  when "starting_run"
    Rails.logger.info "Starting run" 
  else
    Rails.logger.error "Unknown"
end

I can find no methods that would fit for <???> above. Perhaps someone more familiar with this gem could assist please?

Answer 1

You can accept an argument on your before_transition callback and obtain all data you need to implement an expected behaviour.

The code which passes the argument you can find at the source code of the library. You can implement this logic with around_transition as well.

require 'state_machines'

class Light

  state_machine :state, initial: :off do

    before_transition from: any, do: :log_me

    event :light do
      transition all => :on
    end

    event :dark do
      transition [:on] => :off
    end

  end

  def log_me(transition)
    case transition.event
    when :light
      p "`light` event was called to transition from #{transition.from} to #{transition.to}"
    when :dark
      p "`dark` event was called to transition from #{transition.from} to #{transition.to}"
    else
      p "`#{transition.event}` was called to transition from #{transition.from} to #{transition.to}"
    end
  end
end

a = Light.new

a.light # => "`light` event was called to transition from off to on"
a.dark # => "`dark` event was called to transition from on to off"