class Parent
  include Mongoid::Document
  include Mongoid::Timestamps

  embeds_one :child, cascade_callbacks: true
end

class Child
  include Mongoid::Document
  include Mongoid::Timestamps

  after_save :run_callback

  field :updateable_field

  embedded_in :parent

  def run_callback
    puts("after save my updated_at time is #{updated_at}")
  end
end

puts("Create the starting conditions")
parent = Parent.new
parent.child = Child.new

puts("Save the parent, which will output a string where {{updated_at}} is nil in the after_save run_callback on Child")
parent.save!

puts("Show the updated_at values _are_ set correctly afterwards")
puts("Parent updated at #{parent.updated_at}, Child updated at #{parent.child.updated_at}")

puts("Update the Child and save it directly - {{updated_at}} in callback is correct")
parent.child.updateable_field = 'new_value'
parent.child.save!

puts("Update the Child and save the Parent - {{updated_at}} in callback is incorrect")
parent.child.updateable_field = 'newer_value'
parent.save!

puts("But again, afterwards, it _is_ correct")
puts("Parent updated at #{parent.updated_at}, Child updated at #{parent.child.updated_at}")

Create the starting conditions

Save the parent, which will output a string where {{updated_at}} is nil in the after_save run_callback on Child            
after save my updated_at time is

Show the updated_at values _are_ set correctly afterwards
Parent updated at 2022-12-16 10:47:48 UTC, Child updated at 2022-12-16 10:47:48 UTC

Update the Child and save it directly - {{updated_at}} in callback is correct
after save my updated_at time is 2022-12-16 10:59:28 UTC

Update the Child and save the Parent - {{updated_at}} in callback is incorrect
after save my updated_at time is 2022-12-16 10:59:28 UTC 

But again, afterwards, it _is_ correct
Parent updated at 2022-12-16 11:00:00 UTC, Child updated at 2022-12-16 11:00:00 UTC