There is a bug introduced from Rails 3.0.0 -> 3.0.1

It changes the way new models are saved when their class has "accepts_nested_attributes_for" set and one of the associations is not a new record. 


ActiveRecord::RecordNotFound: Couldn't find Account with ID=1 for Customer with ID=
/...../activerecord-3.0.1/lib/active_record/nested_attributes.rb:413:in `raise_nested_attributes_record_not_found'

Here is the ticket: https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/6314-accepts_nested_attributes_for


Here is a github project, that has the error.

https://github.com/23inhouse/accepts_nested_attributes_test.git
git://github.com/23inhouse/accepts_nested_attributes_test.git

You can clone the project.

bundle install
rake db:migrate
rake test:functional

then edit the Gemfile and change:

# gem 'rails', '3.0.1' # fails

to this

gem 'rails', '3.0.0' # passes

bundle update
rake test:functional