There are cases where default value is not set in STI since Rails 8.0.1

[k-tsuchiya-jp]

Steps to reproduce

$ rails _8.0.1_ new hoge_app
$ cd hoge_app
$ rails g model vehicle type:string color:string price:integer release_date:datetime
$ rails g model car --parent=Vehicle
$ rails db:migrate

# Gemfile
source "https://rubygems.org"

gem "rails", "~> 8.0.1"
gem "default_value_for"

# app/models/vehicle.rb
class Vehicle < ApplicationRecord
  default_value_for :color, "black"
end

# app/models/car.rb
class Car < Vehicle
  default_value_for :price, 100
  default_value_for :release_date, DateTime.now
end

$ bundle install
$ rails r 'p Car.new'
#<Car id: nil, type: "Car", color: "black", price: nil, release_date: "2024-12-26 04:30:36.002660000 +0000", created_at: nil, updated_at: nil>

Expected behavior

$ rails r 'p Car.new'
#<Car id: nil, type: "Car", color: "black", price: 100, release_date: "2024-12-26 04:30:36.002660000 +0000", created_at: nil, updated_at: nil>

Actual behavior

• price is set to nil

System configuration

Rails version: 8.0.1
Ruby version: 3.3.5
DefaultValueFor version: 4.1.0

Additional information

It seems to be caused by the modification of class_attribute method in Rails 8.0.1.
rails/rails#53640

[k-tsuchiya-jp]

Before Rails 8.0.1, inherited singleton methods were included in singleton_methods(false), but starting from Rails 8.0.1, inherited singleton methods are no longer included in singleton_methods(false).
As a result, init_hash is always set to true, causing only one attribute in the child class to have its default value set.

default_value_for/lib/default_value_for.rb

Lines 78 to 85 in 2196b23

	else
	init_hash = !singleton_methods(false).include?(:_default_attribute_values)
	end
	if init_hash
	self._default_attribute_values = {}
	self._default_attribute_values_not_allowing_nil = []
	end

[jrafanie]

Thank you @k-tsuchiya-jp for this very good bug report with rails 8. Thank you for the bug report and the proposed solution in #101. I'll review it over there.

[jrafanie]

@k-tsuchiya-jp pushed 4.1.1... thanks again!

[k-tsuchiya-jp]

@jrafanie
Thank you for Merge and Release!
I was on vacation for New Year holidays.
I appreciate your support.