Passing parameters to acts_as_state_machine events

Posted by: Jake Dempsey on: January 19, 2010

• In: Ruby | Ruby on Rails
• Comment!

This morning I ran into a small roadblock working with the acts_as_state_machine gem. My code started like this:

class Communication < ActiveRecord::Base
  include AASM
  aasm_column :status

  aasm_state :draft
  aasm_state :pending
  aasm_state :approved
  aasm_state :rejected

  aasm_event :submit do
    transitions :to => :pending, :from => :draft
  end

  aasm_event :approve do
    transitions :to => :approved, :from => [:pending, :rejected]
  end

  aasm_event :reject do
    transitions :to => :rejected, :from => [:pending, :approved], :guard => :validate_rejection_reason
  end

  aasm_initial_state :draft

  def validate_rejection_reason
    if self.rejection_reason
      true
    else
      raise AASM::InvalidTransition.new('A rejection reason is required')
    end
  end
end

This is a basic example using AASM to provide an approval process for my Communication model. I wanted the ability to just call instance.reject(“some reason”) or instance.reject!(“some reason”). I was really thinking to hard about it. The assm_event just creates some methods for me….so why not just decorate those methods using ruby aliases. This is what I ended up with:

  include AASM
  aasm_column :status

  aasm_state :draft
  aasm_state :pending
  aasm_state :approved
  aasm_state :rejected

  aasm_event :submit do
    transitions :to => :pending, :from => :draft
  end

  aasm_event :approve do
    transitions :to => :approved, :from => [:pending, :rejected]
  end

  aasm_event :reject do
    transitions :to => :rejected, :from => [:pending, :approved], :guard => :validate_rejection_reason
  end
  alias old_reject reject
  alias old_reject! reject!

  aasm_initial_state :draft

  def reject(reason)
    self.rejection_reason = reason
    self.old_reject
  end

  def reject!(reason)
    self.rejection_reason = reason
    self.old_reject!
  end

  def validate_rejection_reason
    if self.rejection_reason
      true
    else
      raise AASM::InvalidTransition.new('A rejection reason is required')
    end
  end

Notice the use of alias for reject and reject!. Now you have to call reject with a rejection reason. There may be another way to get parameters in to the event call….but this is how I rolled mine