Nested_for_form不显示field_for的字段

MY view is

我的观点是

<h3> Register New Items </h3>
<div class="row">
<div class="span2 offset4">
<%= nested_form_for @item_categories, :url => items_path, :method => :post, :html => { :class => "item_category"} do |f| %>
        <div><%= f.label :item_name %>
        <%= f.text_field :item_name %></div>
        </br>
         <% f.fields_for :item_companies do |c| %>
              <%= c.text_field :company_name %></div>
         <%end%>
        <div><%= f.submit "Submit" %></div>
    <% end %>
</div>
<h3> Register New Items <