require "bundler/inline"

gemfile do
  source "https://rubygems.org"
  gem "mongoid", "9.1.0"
end

require "mongoid"

Mongoid.configure do |config|
  config.clients.default = {
    hosts: [ENV.fetch("MONGO_HOST", "localhost:27017")],
    database: "mongoid_embeds_many_clear_repro",
    options: { direct_connection: true }
  }
end
Mongoid.logger.level = Logger::WARN
Mongo::Logger.logger.level = Logger::WARNclass Root
  include Mongoid::Document
  embeds_one :section
end

class Section
  include Mongoid::Document
  embedded_in :root
  embeds_many :items
end

class Item
  include Mongoid::Document
  embedded_in :section
  field :name, type: String
end

Root.collection.dropdef stored_item_names(root)
  doc = Root.collection.find(_id: root.id).first
  Array(doc && doc.dig("section", "items")).map { |item| item["name"] }
end

root = Root.create!
section = root.build_section
section.items.build(name: "one")
section.items.build(name: "two")
root.save! # memoizes the root's _descendants while building the atomic update
puts "after build + save: #{stored_item_names(root).inspect}" # => ["one", "two"]
root.section.items.clear
puts "after clear:        #{stored_item_names(root).inspect}" # => [] ($unset was issued)
puts "in memory:          #{root.section.items.map(&:name).inspect}" # => []
root.save!
puts "after save:         #{stored_item_names(root).inspect}" # => ["one", "two"] (!!)
puts "in memory:          #{root.section.items.map(&:name).inspect}" # => []
puts "reloaded:           #{Root.find(root.id).section.items.map(&:name).inspect}" # => ["one", "two"]