Full code for http://code.dblock.org/2015/01/15/first-class-mongoid-queries-with-collection-snapshots.html

2015-01-15-first-class-mongoid-queries-with-collection-snapshots.rb

require 'mongoid'
require 'mongoid_collection_snapshot'

Mongoid.load!("mongoid.yml", :development)

class Widget
  include Mongoid::Document

end

class Gadget
  include Mongoid::Document

end

class WidgetAndGadget
  include Mongoid::Document

  belongs_to :widget, inverse_of: nil
  belongs_to :gadget, inverse_of: nil

  def self.pair!
    WidgetAndGadget.destroy_all
    Widget.all.each do |widget|
      Gadget.all.each do |gadget|
        WidgetAndGadget.create!(widget: widget, gadget: gadget) if Random.rand(2) == 1
      end
    end
  end

  def self.pair_incrementally!
    widgets_and_gadgets = []
    Widget.all.each do |widget|
      Gadget.all.each do |gadget|
        next unless Random.rand(2) == 1
        widget = WidgetAndGadget.where(widget: widget, gadget: gadget).first
        widget ||= WidgetAndGadget.create!(widget: widget, gadget: gadget)
        widgets_and_gadgets << widget
      end
    end
    (WidgetAndGadget.all.to_a - widgets_and_gadgets).each do |pair|
      pair.destroy
    end
  end
end

class WidgetsAndGadgets
  include Mongoid::CollectionSnapshot

  document do
    belongs_to :widget, inverse_of: nil
    belongs_to :gadget, inverse_of: nil
  end

  def build
    Widget.all.each do |widget|
      Gadget.all.each do |gadget|
        next unless Random.rand(2) == 1
        collection_snapshot.insert(widget_id: widget.id, gadget_id: gadget.id)
      end
    end
  end
end

=begin
Widget.delete_all
Gadget.delete_all

10.times { Widget.create! }
10.times { Gadget.create! }

WidgetAndGadget.pair!
puts "#{WidgetAndGadget.count} widgets and gadgets paired!"

WidgetAndGadget.pair_incrementally!
puts "#{WidgetAndGadget.count} widgets and gadgets paired incrementally!"
=end

index1 = WidgetsAndGadgets.create!
puts "#{index1.collection_snapshot.find.count} widgets and gadgets paired incrementally!"

index2 = WidgetsAndGadgets.create!
puts "#{index2.collection_snapshot.find.count} widgets and gadgets paired incrementally!"

WidgetsAndGadgets.latest.documents.each do |pair|
  puts "#{pair.widget} x #{pair.gadget}"
end

Gemfile

source 'http://rubygems.org'

gem 'mongoid'
gem 'mongoid_collection_snapshot', github: 'dblock/mongoid_collection_snapshot', branch: 'collection-snapshot-mongoid'

mongoid.yml

development:
  sessions:
    default:
      database: first-class-mongoid-queries
      hosts:
        - localhost:27017