active_record_type_issue.rb

require 'bundler/inline'

gemfile(true) do
  source 'https://rubygems.org'

  gem 'rails', github: 'rails/rails'
  gem 'sqlite3'
  gem 'uuidtools'
end

require 'active_record'
require 'minitest/autorun'
require 'logger'

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table 'tokens', id: :binary, limit: 16, force: true
  create_table 'users', force: true

  create_table 'token_users', force: true do |t|
    t.integer 'user_id'
    t.binary 'token_id', limit: 16, null: false
  end
end

class UuidType < ActiveRecord::Type::Binary
  def serialize(value)
    super(cast_to_uuid(value)&.raw)
  end

  def deserialize(value)
    cast_to_uuid(super(value)).to_s
  end

  def cast_value(value)
    cast_to_uuid(value).to_s
  end

  private

  def cast_to_uuid(value)
    return if value.nil?

    case value.size
    when 16 then UUIDTools::UUID.parse_raw(value)
    when 36 then UUIDTools::UUID.parse(value)
    end
  end
end

class User < ActiveRecord::Base
end

class Token < ActiveRecord::Base
  attribute :id, UuidType.new, default: SecureRandom.uuid

  has_many :token_users
  has_many :users, through: :token_users
end

class TokenUser < ActiveRecord::Base
  attribute :token_id, UuidType.new

  belongs_to :user
  belongs_to :token
end

class IssueTest < Minitest::Test
  def test_association_with_uuid
    token = Token.create!
    token.users << User.create!

    assert_equal 1, token.reload.token_users.count
    assert_equal 1, token.reload.users.count
  end
end

https://stackoverflow.com/questions/55446330/has-many-through-association-doesnt-work-when-using-a-custom-activerecordty