访问父模型中的嵌套子属性？

Question

I have the following form for release, with fields for tracks being accepted as nested attributes within my release model.

<%= form_for(@release) do |f| %>
<%= f.hidden_field :user_id, :value => current_user.id, :class => "text" %>
<%= f.text_field :title, :class => "text" %>

<%= f.fields_for :tracks do |builder| %>
<%= render 'track_fields', :f => builder %>
<% end %>

<% end %>

My release model contains:

  accepts_nested_attributes_for :tracks, :reject_if => lambda { |a| a[:name].blank? }, :allow_destroy => :true
  accepts_nested_attributes_for :releases_tracks

  before_save :order_tracks
  before_update :order_tracks


  def order_tracks 
    releases_tracks.each { |t| t.position = track_attributes.position }
    tracks.each { |t| t.user_id = user_id}
    tracks.each { |t| t.label_id = label_id}
  end

  def track_attributes=(track_attributes)
    track_attributes.each do |attributes|
    tracks.build(attributes)
    artists_tracks.build(attributes)
    end
  end

Everything works well, except the line below where i'm trying to take the position value entered in the fields_for part of the form. I can access values from the parent form, user_id for example, but how do I access the child values?

releases_tracks.each { |t| t.position = track_attributes.position }

Thanks all!

(Note: I don't want to use acts_as_list for this)

Answer 1

try to use:

releases_tracks.each { |t| t.position = track_attributes[:position] }  or 
releases_tracks.each { |t| t.position = track_attributes["position"] }