Broken code that should update Mongo document.

gistfile1.rb

#!/usr/bin/env ruby

#
# This is intended to test Mongo's atomic-update operation. It fails; see below.
#

require 'mongomatic'

class VideoGroup < Mongomatic::Base

  Mongomatic.db = Mongo::Connection.new.db('mydatabase')

end

#
# first set up a sample database with a video groups with a couple of videos
#

VideoGroup.drop

video_group = VideoGroup.new
video_group['videos'] = [
  {
    'video_id' => 'video1',
  },
  {
    'video_id' => 'video2',
  },
]
video_group.insert

#
# now update just one video in the video group
#

video_group = VideoGroup.find_one('videos.video_id' => 'video1') or raise "Failed to find video group"

video_group.update!({ 'videos.video_id' => 'video1' }, '$set' => {
  'videos.$.views' => 123,
})
#XXX this fails with 'can't append to array using string field name [$]'

#
# finally check to make sure the video got properly updated
#

video_group = VideoGroup.find_one('videos.video_id' => 'video1') or raise "Failed to find video group"
video = video_group['videos'].find { |v| v['video_id'] == 'video1' }
raise "Failed to set video attributes" unless video['views'] == 123