Can't mass-assign protected attributes: quantities - ruby-on-rails

Question

I'm getting this error:
Can't mass-assign protected attributes: quantities
I looked up all the threads concerning this issue in the site, but couldn't find something to answer my problem. Here are the code snippets:
product.rb
class Product < ActiveRecord::Base
attr_accessible :name, :quantities_attributes
has_many :quantities
accepts_nested_attributes_for :quantities, :allow_destroy => :true,
:reject_if => proc { |attrs| attrs.all? { |k, v| v.blank? } }
new.html.erb
<% if #was_submitted %>
<%= form_for(:new_product_array, :url => products_path) do |f| %>
<% prefix ||= 0 %>
<% #new_product_array.each do |n| %>
<% n.quantities.build %>
<% prefix += 1 %>
<%= f.fields_for(prefix.to_s ) do |child| %>
<div class="field">
<%= child.label :name %><br />
<%= child.text_field :name%>
</div>
<%= render :partial => 'quantities/form',
:locals => {:form => child} %>
<% end %>
<% end %>
<div class="actions">
<%= submit_tag :submit %>
</div>
<% end %>
<% else %>
<%= form_tag new_product_path, :method => 'get' do %>
<p align=center>
How many Items are you Adding? (1-100)
<%= number_field_tag 'amount', 1, :in => 1...100 %>
</br>
To which storage?
<%= number_field_tag 'storage', 1, :in => 1...100 %>
<%= submit_tag "Next", :name => 'submitted' %>
</p>
<% end %>
<% end %>
<%= link_to 'Back', products_path %>
product_controller.rb
def new
#product = Product.new
if params['submitted']
#was_submitted = true
#amount_form = params['amount']
#new_product_array = []
(1..#amount_form.to_i).each do
#new_product_array << Product.new
end
#storage_form = params['storage']
else
#was_submitted = false
end
respond_to do |format|
format.html # new.html.erb
format.json { render :json => #product }
end
end
def create
i=0
logger.info params[:new_product_array].inspect
params[:new_product_array].each do |new_product|
if new_product.last[:name] != nil
#new_product_array[i] = Product.new(new_product.last)
#new_product_array[i].save
i+=1
end
end
redirect_to(products_path)
end
quantity.rb
class Quantity < ActiveRecord::Base
belongs_to :product
attr_accessible :amount, :storage
end
quantity/_form.html.erb
<%= form.fields_for :quantities do |quant| %>
<div class="field">
<%= quant.label :storage %><br />
<%= quant.number_field :storage %>
</div>
<div class="field">
<%= quant.label :amount %><br />
<%= quant.number_field :amount %>
</div>
<% unless quant.object.nil? || quant.object.new_record? %>
<div class="field">
<%= quant.label :_destroy, 'Remove:' %>
<%= quant.check_box :_destroy %>
</div>
<% end %>
<% end %>
Overall what Im trying to do, is ask the user how much products to add, then make a form with the number of fields the user specifies and with one submit button add all of the products, whereas when you add a product you also add a quantity record which holds more information on the product.

Answer 1

You need a line like this:
attr_accessible :name, :quantities_attributes, :quantities

Answer 2

You have very bad code, it can be much simplier 100%.
Your problem is that form dont' know nothing about your resource (product), so it can't render 'smartly' fields "quantities_attributes", it renders "quantities" instead.