Rails - Dec 2012 - Multiple checkboxes for a has_many through not saving

*I Copied this from StackOverflow since I did not get any response there. 
There is an update at the end. *

I am not sure why my checkboxes for a has_many through are not saving. This 
is a rather complex form (An online application for a language summer 
program) so in addition to regular applicant information, I am collecting 
attributes of a LanguageBackgroundAndInterest model using a fields_for. 
Part of these attributes are the books that the applicant used to learn the 
language. The code looks like this:

    <%= f.fields_for :language_background_and_interest do |builder| %>
      <div class="field"> 
      <%= hidden_field_tag
"language_background_and_interest[book_ids][]" %>
      <% Book.all.each do |book| %>
        <br><%= check_box_tag
"language_background_and_interest[book_ids][]", book.id %>
        <%= book.name.humanize %>
      <% end %>
      </div>
    <% end %>

Both the language_background_and_interest and books are joined together 
using a has_many_through like so:

class LanguageBackgroundAndInterest < ActiveRecord::Base
  attr_accessible :book_ids

  has_many :language_background_books
  has_many :books, through: :language_background_booksend
class Book < ActiveRecord::Base
  attr_accessible :name, :publisher

  has_many :language_background_books
  has_many :language_background_and_interests, through:
:language_background_booksend
# Join Tableclass LanguageBackgroundBook < ActiveRecord::Base
  attr_accessible :language_background_and_interest_id, :book_id
  belongs_to :language_background_and_interest
  belongs_to :bookend

I am not sure why the books from the checkboxes don''t get assigned to
the
appropriate background model. Any ideas?

PS: Granted, this design is rather ambiguous (Why not make books belong to 
an applicant?), but I currently want to put up a prototype and I am also 
constrained by a dubious requirement. So I need this working.

Update: 

I appended the word "attributes" bellow to the language_background
model in
the hope that the books_ids array gets inserted properly into the params 
hash with the other attributes. Inspecting the development.log, I can see 
the key language_background_and_interest_attributes twice: One for all the 
other data which get successfully saved, and one for the book_ids array 
which apparently gets ignored. Any ideas?

    <%= f.fields_for :language_background_and_interest do |builder| %>
      <div class="field"> 
      <%= hidden_field_tag
"language_background_and_interest_attributes[book_ids][]" %>
      <% Book.all.each do |book| %>
        <br><%= check_box_tag
"language_background_and_interest_attributes[book_ids][]", book.id
%>
        <%= book.name.humanize %>
      <% end %>
      </div>
    <% end %>

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On Dec 26, 12:15 am, why-el
<wael.khobala...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> I appended the word "attributes" bellow to the
language_background model in
> the hope that the books_ids array gets inserted properly into the params
> hash with the other attributes. Inspecting the development.log, I can see
> the key language_background_and_interest_attributes twice: One for all the
> other data which get successfully saved, and one for the book_ids array
> which apparently gets ignored. Any ideas?
>
What does that log look like? You''d probably need to nest it in the
hash for the parent attributes ie
some_model[language_background_and_interest_attributes][some_id]
[book_ids]

The some_id for a saved record would be just its id. If you''re adding
fields on the fly, then you''ll have to have the matching id - check
what other parameters get submitted

Fred

>     <%= f.fields_for :language_background_and_interest do |builder|
%>
>       <div class="field">
>       <%= hidden_field_tag
"language_background_and_interest_attributes[book_ids][]" %>
>       <% Book.all.each do |book| %>
>         <br><%= check_box_tag
"language_background_and_interest_attributes[book_ids][]", book.id
%>
>         <%= book.name.humanize %>
>       <% end %>
>       </div>
>     <% end %>
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