accepts_nested_attributes_for + belongs_to does not show fields

See more:

Ruby

I have two models:

class User < ActiveRecord::Base
  acts_as_authentic
  has_many :orders
end

and

class Order < ActiveRecord::Base
  belongs_to :user
  accepts_nested_attributes_for :user
end

The idea is that if the user is already logged in, I just want to make an order for that user, but if he is not logged in, then I will ask him to register in the same time as making an order. Here is the form for orders:

<%= form_for(@order) do |f| %>
  <div class="field">
    <%= f.label :quantity %><br />
    <%= f.number_field :quantity %>
  </div>

  <% if current_user %>
  <div class="field">
    <%= current_user.email%>
  </div>
  <%else%>
    <%= f.fields_for(:user) do |user_form| %>
        <%= render "newuser_fields", :f => user_form %>
    <% end %>
  <% end %>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

and new users fields are:

<div class="field">
  <%= f.label :email %><br />
  <%= f.text_field :email %>
</div>
<div class="field">
  <%= f.label :password %><br />
  <%= f.password_field :password %>
</div>
<div class="field">
  <%= f.label :password_confirmation %><br />
  <%= f.password_field :password_confirmation %>
</div>

The problem is that it won't show fields for user!

Any suggestions?