title: rails ActiveAdmin nested form has_one accepts_attributes_for formtastic issue
body: <p>I am using ActiveAdmin and Rails 3.1 -- having problem understanding whether the following is a bug, or if there is some way to do it correctly that I am not understanding. I am trying to use a nested model with a has one relationship, so that I can create a page and fill out it's meta data in 1 step. --
  (page has_one meta_data, accepts_nested_attributes_for meta_data)</p>
  
  <p><strong>Example 1)</strong>
  in this example, when I click new page, meta data section is there but there are no input fields -- also, if I edit the record, it shows up correctly, however the fieldset is duplicated in the second section... and if I remove the f.inputs wrapping semantic_field_for (which would make sense), then it breaks completely and shows nothing in the meta data area...</p>
  
  <pre><code>form do |f|
    f.inputs "Page Information" do
      f.input :name
      f.input :uri
      f.input :view
      f.input :body, :as =&gt; :text
      f.input :active
    end
  
    f.inputs "Meta Data" do
      f.semantic_fields_for :meta_data do |meta_form|
        meta_form.inputs :title, :description, :keywords, :name =&gt; "Meta Information"
      end
    end  
  end
  </code></pre>
  
  <p>I understand the meta data probably isn't being instantiated, but I am not sure how I am supposed to do that in the form block? (or if I can even do it) -- The only way I am able to get this to work is by doing using a custom form, and building the meta data in the view, which looks like this</p>
  
  <p><strong>2) How I am working around it, but seems hacky</strong></p>
  
  <pre><code>&lt;%= semantic_form_for [:admin, @page] do |f| %&gt;
    &lt;% @page.build_meta_data %&gt;
    &lt;%= f.inputs :name =&gt; "Page Information" do  %&gt;
      &lt;%= f.input :name %&gt;
      &lt;%= f.input :uri %&gt;
      &lt;%= f.input :view %&gt;
      &lt;%= f.input :body, :as =&gt; :text %&gt;
      &lt;%= f.input :active %&gt;
    &lt;% end %&gt;
    &lt;%= f.semantic_fields_for :meta_data do |meta_form| %&gt;
      &lt;%= meta_form.inputs :title, :description, :keywords, :name =&gt; "Meta Information" %&gt;
    &lt;% end %&gt;
  
    &lt;%= f.buttons %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>Thanks in advance for any help or clarification.</p>
  
  <p>(note to moderators I started another thread on this but was not as clear and didn't have the workaround solution I do now yet, so if one of the questions should be deleted please delete the other)</p>