Q:

Multiple checkboxes for a has_many through not saving

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_books
end

class Book < ActiveRecord::Base
  attr_accessible :name, :publisher

  has_many :language_background_books
  has_many :language_background_and_interests, through: :language_background_books
end

# Join Table
class LanguageBackgroundBook < ActiveRecord::Base
  attr_accessible :language_background_and_interest_id, :book_id
  belongs_to :language_background_and_interest
  belongs_to :book
end

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. 

A:

I ended up reviewing my model design and simplified it. I also switched to Simple Form to ease up working with my complex forms. 

