Basic AggregateRoot pattern implementation.

my_aggregate_root.rb

module MyAggregateRoot
  def load(stream_name, event_store:)
    @version = -1
    event_store.read.stream(stream_name).forward.each do |event|
      apply(event)
      @version += 1
    end

    @stream_name        = stream_name
    @unpublished_events = []
  end

  def apply(event)
    send("apply_#{event.class.to_s.demodulize.underscore}", event)

    unpublished_events.push(event)
  end

  def store(event_store:)
    unpublished_events.each do |event|
      event_store.publish(
        event,
        stream_name:      @stream_name,
        expected_version: version
      )

      @version += 1
    end

    @unpublished_events = []
  end

  def unpublished_events
    @unpublished_events ||= []
  end

  def version
    @version ||= -1
  end
end