Nested Attributes and Unpermitted parameters - ruby-on-rails

Question

I have a form that is passing nested attributes it works for the 'Child' but the 'books' don't appear to be saving.
I have 3 models. Each Child can have 2 books:
class Child < ActiveRecord::Base
has_many :hires
has_many :books, through: :hires
end
class Hire < ActiveRecord::Base
belongs_to :book
belongs_to :child
accepts_nested_attributes_for :book
accepts_nested_attributes_for :child
end
class Book < ActiveRecord::Base
has_many :hires
has_many :children, through: :hires
belongs_to :genres
end
The controller looks like this:
class HiresController < ApplicationController
...
def new
#hire = Hire.new
2.times { #hire.build_book }
end
def create
#hire = Hire.new(hire_params)
respond_to do |format|
if #hire.save
format.html { redirect_to #hire, notice: 'Hire was successfully created.' }
format.json { render :show, status: :created, location: #hire }
else
format.html { render :new }
format.json { render json: #hire.errors, status: :unprocessable_entity }
end
end
end
...
private
# Use callbacks to share common setup or constraints between actions.
def set_hire
#hire = Hire.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def hire_params
params.require(:hire).permit(:child_id, books_attributes: [ :id, :book_id, :_destroy])
end
end
The hash that is being submitted looks like this:
Processing by HiresController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"+2xxx==", "hire"=>{"child_id"=>"2", "books"=>{"book_id"=>"5"}}, "commit"=>"Create Hire"}
Unpermitted parameter: books
I can't work out why i'm getting the unpermitted params error? Any advice?
* EDIT - included the view as I now suspect this might play a part *
<%= form_for(#hire) do |f| %>
<%= f.select(:child_id, Child.all.collect {|a| [a.nickname, a.id]}) -%>
<%= f.label :child_id %><br>
<%= f.fields_for :books do |books_form| %>
<%= books_form.label :book_id %><br>
<%= books_form.select(:book_id, Book.all.collect {|a| [a.Title, a.id]}) -%>
<%= books_form.label :book_id %><br>
<%= books_form.select(:book_id, Book.all.collect {|a| [a.Title, a.id]}) -%>
<% end %>
<div class="actions">
<%= f.submit %>
</div>
<% end %>

Answer 1

You need to use the following:
#app/controllers/hires_controller.rb
class HiresController < ApplicationController
def new
#hire = Hire.new
2.times do
#hire.build_book
end
end
end
The rest of it looks okay.
The problem you have is pretty typical; when you use f.fields_for, you have to build the associative objects, otherwise the fields_for won't create the correct field names.
The field names you're looking for will be [books_attributes][0][book_id] etc.
Since your form is passing all the attributes you'd expect (without the _attributes suffix), I can only surmise that your building of the associated objects is incorrect:
2.times { #hire.books.build }
... should be ...
2.times { #hire.build_book }
When you have singular associations, you have to build the associative object singularly: build_object, whilst with plural, you can use the plural.build call.