title: accepts_nested_attributes_for + belongs_to does not show fields
body: <p>I have two models:</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    acts_as_authentic
    has_many :orders
  end
  </code></pre>
  
  <p>and</p>
  
  <pre><code>class Order &lt; ActiveRecord::Base
    belongs_to :user
    accepts_nested_attributes_for :user
  end
  </code></pre>
  
  <p>the idea is that if the user is already logged in, I just want to make a order for that user, but if he is not logged in, then I will ask him to register in the same time as making order. 
  here is the form for orders</p>
  
  <pre><code>&lt;%= form_for(@order) do |f| %&gt;
    &lt;div class="field"&gt;
      &lt;%= f.label :quantity %&gt;&lt;br /&gt;
      &lt;%= f.number_field :quantity %&gt;
    &lt;/div&gt;
  
    &lt;% if current_user %&gt;
    &lt;div class="field"&gt;
      &lt;%= current_user.email%&gt;
    &lt;/div&gt;
    &lt;%else%&gt;
      &lt;%= f.fields_for(:user) do |user_form| %&gt;
          &lt;%= render "newuser_fields", :f =&gt; user_form %&gt;
      &lt;% end %&gt;
    &lt;% end %&gt;
    &lt;div class="actions"&gt;
      &lt;%= f.submit %&gt;
    &lt;/div&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>and new users fields are:</p>
  
  <pre><code>&lt;div class="field"&gt;
    &lt;%= f.label :email %&gt;&lt;br /&gt;
    &lt;%= f.text_field :email %&gt;
  &lt;/div&gt;
  &lt;div class="field"&gt;
    &lt;%= f.label :password %&gt;&lt;br /&gt;
    &lt;%= f.password_field :password %&gt;
  &lt;/div&gt;
  &lt;div class="field"&gt;
    &lt;%= f.label :password_confirmation %&gt;&lt;br /&gt;
    &lt;%= f.password_field :password_confirmation %&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>The problem is that it won't show fields for user!</p>
  
  <p>Any suggestions?</p>