simple nested form question

hi, im having a 1<>N, Bol<>BolLines model, and trying to use nested urls, but the form is confusing me..maybe someone can enlighten me:

url: http://192.168.0.111:3000/bols/6/bol_lines/new

<% form_for @bol_line do |f| %>   <%= f.error_messages %>

<!-- PROBLEM   <p>     <%= f.label :bol_id %><br />     <%= f.text_field :bol_id %>   </p> <!-- PROBLEM

  <p>     <%= f.label :package_type_id %><br />     <%= f.collection_select :package_type_id, PackageType.all, :id, :title %>   </p>

  <p>     <%= f.label :item_id %><br />     <%= f.collection_select :item_id, Item.find(:all, :order => :title ), :id, :title %>   </p>

  <p>     <%= f.label :amount_packages %><br />     <%= f.text_field :amount_packages %>   </p>   <p><%= f.submit "Submit" %></p> <% end %>

problem: leaving the as "problem" commented lines out, im lossing my "parent_id", since it doesnt get posted. (this happens all in the EDIT-view). now is this correct or am i doing something wrong? thx tom