While trying to upgrade from 7.5.1 to 8.0.2 I noticed the new "uncastable type" behavior documented here: https://www.mongodb.com/docs/mongoid/master/release-notes/mongoid-8.0/#storing-retrieving-evolving-uncastable-values.

And unfortunately it created a lot of failures in my application where I use ActiveSupport::Duration (e.g. 5.minutes, 2.hours, 23.seconds, etc..). These types are castable to Integer and Float and usually stored in these kind of fields depending on the precision wanted so they are definitely not "uncastable". I have them stored in Float for the last 10 years and noticed they are not accepted any more, it just keeps nil since 8.0.2. I thought: Ok that's annoying but maybe that's what AR does so it could make sense to align even if would be pretty annoying to have to manually convert everywhere, but AFAICS it's not the case, I just tested in AR 7.0.3.1 (latest version) and it casts duration to integer or float attributes without problem.

So before spending hours rewriting my app for a potential bug, I would rather ask if breaking this is actually a desired divergence from AR in Mongoid ? And what would justify this ? I support this is more likely a missed case in the way Mongoid casts values which doesn't play well with Duration? (I suppose it doesn't use the standard `to_f`? because Duration responds to it).

Here is a simple reproduction example:

#!/usr/bin/env ruby

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'mongoid', '7.5.1'
  gem 'activesupport'
end

require 'mongoid'

Mongoid.configure { |c| c.clients.default = { hosts: ['localhost'], database: 'test' } }
puts Mongoid::VERSION
puts Mongo::VERSION

class Model
  include Mongoid::Document
  include Mongoid::Timestamps

  field :a, type: Integer
  field :b, type: Float
end

model = Model.new(a: 2.hours, b: 1.minute / 178.0)
p model
# With 8.0.2:
#<Model _id: 62e93da5756457011a9a825f, created_at: nil, updated_at: nil, a: nil, b: nil>

# With 7.5.1:
#<Model _id: 62e93dcd756457019ae0d98a, created_at: nil, updated_at: nil, a: 7200, b: 0.33707865168539325>

p 2.hours.to_i
# 7200
p 2.hours.to_f
# 7200.0

Thanks for the clarification and sorry if I missed any existing discussion about this, I searched for it but couldn't find anything yet.