Context

Using `Mongoid::Timestamps` in parent as well as embedded documents, requires to enable `cascaded_callbacks` to the relationship, provided that `parent.save` will also `touch` the `updated_at` date of the embedded docs.

Mongoid::VERSION
# => "6.4.2" 

• After[ researching among issues and fixes|https://jira.mongodb.org/browse/MONGOID-3282?jql=project%20%3D%20%2212981%22%20AND%20text%20~%20%22timeless%22%20ORDER%20BY%20priority%20DESC%2C%20updated%20DESC], I could not see any related bug report.

The issue

Looking at the code, it seems that it makes sure that `cascadable_children` gets their own `timeless` (count increment). However, for some reason, this doesn't work as expected?

Recreation

The embedded document

class Bar
  include Mongoid::Document
  include Mongoid::Timestamps
  embedded_in :foo, class_name: "Foo"
  
  field :completed, type: Boolean, default: false
  field :baz, type: String
end 

The root/parent document

class Foo
  include Mongoid::Document
  include Mongoid::Timestamps
  
  embeds_many :bars, class_name: "Bar", cascade_callbacks: true
  
  field :completed, type: Boolean, default: false
end 

The test case

foo = Foo.create({bars: [{baz: "baz"}]})
foo.updated_at
# => Fri, 07 Jun 2024 04:46:45.187964828 NZST +12:00 
foo.bars.first.updated_at
# => Fri, 07 Jun 2024 04:46:45.187867405 NZST +12:00

• Observe how both dates are at 4.46 am NZ

The above shows that cascaded_callbacks propagated the `updated_at` change to the embedded doc (`bar`).

Now let's change content and persist with `timeless`:

foo.changed?
# => false

foo.bars.first.completed = true
foo.completed = true

foo.changed?
# => true

foo.timeless.save

foo.updated_at
# => Fri, 07 Jun 2024 04:46:45.187964828 NZST +12:00
foo.bars.first.updated_at
# => Fri, 07 Jun 2024 04:51:08.430987097 NZST +12:00

While the root document (`foo`) has actually preserved the `updated_at` date, the embeded doc got its timestamp updated.