accepts_nested_attributes_for causes duplicate entries in join model table

Tested with 2-3-stable branch and this seems to have been fixed.

I was just gonna ask that :) Thanks for the update.

Which commit was this, or which public release did this get rolled in? As I saw this in 2.3.5, upgraded to 2.3.8, and I'm still seeing it. Here is my model:

class User < ActiveRecord::Base
  has_many :conferences, :through => :conference_attendees, :order => 'end_date DESC'
  has_many :conference_attendees
  accepts_nested_attributes_for, :conferences, :allow_destroy => true
end

class Conference < ActiveRecord::Base
  has_many :users, :through => :conference_attendees
  has_many :conference_attendees, :dependent => :destroy
  accepts_nested_attributes_for :conference_attendees, :allow_destroy => true
end

class ConferenceAttendee < ActiveRecord::Base
  belongs_to :conference
  belongs_to :user
end

@user = User.first
# @user.id == 2
params = {"user"=>{"conferences_attributes"=>{"0"=>{"name"=>"Conf Name", "conference_attendees_attributes"=>{"0"=>{"role"=>"Attendee", "user_id"=>"1984"}}}}}}
@user.update_attributes params['user']

When I run this in Rails 2.3.8, I see the following in my logs:

  Conference Create (0.2ms)   INSERT INTO tech_conferences (name, created_at, updated_at) VALUES('Conf Name', '2010-06-26 03:01:07', '2010-06-26 03:01:07')
  ConferenceAttendee Create (0.2ms)   INSERT INTO tech_conference_attendees (created_at, updated_at, role, user_id, conference_id) VALUES('2010-06-26 03:01:07', '2010-06-26 03:01:07', 'Attendee', 1984, 1124)
  ConferenceAttendee Create (0.7ms)   INSERT INTO tech_conference_attendees (created_at, updated_at, role, user_id, conference_id) VALUES('2010-06-26 03:01:07', '2010-06-26 03:01:07', NULL, 2, 1124)

This varies slightly from the original poster. In my case, the second conference has a NULL value for the 'role' field in ConferenceAttendee, and also has the same user id as the @user although that ID was not specified in the params for ConferenceAttendee.

Also of note: I tried changing my accepts_nested_attributes_for :conference_attendees and added a :reject_if that rejects everything, and ran this again. The first ConferenceAttendee is not created, but the second one is.

My quick-and-dirty workaround for this right now is an after_save that deletes the record if it doesn't have a 'role' attribute, I'm just hoping this kluge doesn't get me fired. :) Please, if you've got a better temporary solution, I'm all ears.