require 'mongoid'

Mongoid.connect_to 'positional_operators_test'

class Artwork
  include Mongoid::Document
  field :title, type: String
  embeds_many :images
end

class Image
  include Mongoid::Document
  embedded_in :artwork
  field :filename, type: String
  field :width, type: Integer
  field :height, type: Integer
end

artwork = Artwork.create!(title: "Mona Lisa")
image1 = Image.new(filename: "framed.jpg")
artwork.images << image1
image2 = Image.new(filename: "unframed.jpg")
artwork.images << image2

#Artwork.collection.where(_id: artwork.id).update("$pull" => { "images" => { _id: image1.id } })
Artwork.collection.find(_id: artwork.id).update_one("$pull" => { "images" => { _id: image1.id } })

image2.update_attributes!(width: 30, height: 40)

p artwork.reload.images.count # should be 1, in Mongoid 5 it's 2