aasm_state_event.rb

module Concerns
  module AasmStateEvent
    extend ActiveSupport::Concern

    included do
      attr_accessor :state_event
    end

    # It behaves just like `save!`, but when `state_event` was set through
    # `assign_attributes` before, `save!` uses the given state with a `!` to
    # persist the record.
    #
    # Example
    # =======
    #
    # ```ruby
    # record.assign_attributes state_event: 'start_engine'
    # record.save! # => actually calles record.start_engine!
    # ```
    #
    def save!
      return super if state_event.blank?
      fail BadRequest.new, 'Event not defined' unless known_state_event?
      send :"#{state_event}!"
    end

    def known_state_event?
      aasm.events.map.include? state_event.to_s.to_sym
    end
  end
end

bad_request.rb

class BadRequest < StandardError
end

You should probably run super at the end of save! method, otherwise you're going to ignore other changes.

Saving the state is also saving the model, isn't it?

I have just checked the code, you are right. I'll change the code then when I have tested it. It will then look like this

    def save!
      return super if state_event.blank?
      fail BadRequest.new, 'Event not defined' unless known_state_event?
      send :"#{state_event}"
      super
    end