title: has_many nested form with a has_one nested form within it
body: <p>I am currently trying to make a form for a model, which has a dynamic number of nested models.  I'm using Nested Forms (as described in <a href="http://railscasts.com/episodes/197-nested-model-form-part-2" rel="nofollow">RailsCasts 197</a>).  To make things even more complicated, each of my nested models has a <code>has_one</code> association with a third model, which I would also like to be added to the form.</p>
  
  <p>For any who are wondering about over normalization or an improper approach, this example is a simplified version of the problem I'm facing.  In reality, things are slightly more complex, and this is the approach we've decided to take.</p>
  
  <p>Some example code to illustrate the problem below:</p>
  
  <pre class="lang-rb prettyprint-override"><code>#MODELS
  class Test 
    attr_accessible :test_name, :test_description, :questions_attributes
    has_many :questions
    accepts_nested_attributes_for :questions
  end
  
  class Question
    attr_accessible :question, :answer_attributes
    belongs_to :test
    has_one :answer
    accepts_nested_attributes_for :answer
  end
  
  class Answer
    attr_accessible :answer
    belongs_to :question
  end
  
  #CONTROLLER
  class TestsController &lt; ApplicationController
  
    #GET /tests/new
    def new
      @test = Test.new
      @questions = @test.questions.build
      @answers = @questions.build_answer
    end
  
  end
  
  #VIEW
  &lt;%= form_for @test do |f| %&gt;
    &lt;%= f.label :test_name %&gt;
    &lt;%= f.text_box :test_name %&gt;
    &lt;%= f.label :test_description %&gt;
    &lt;%= f.text_area :test_description %&gt;
    &lt;%= f.fields_for :questions do |questions_builder| %&gt;
      &lt;%= questions_builder.label :question %&gt;
      &lt;%= questions_builder.text_box :question %&gt;
        &lt;%= questions_builder.fields_for :answer do |answers_builder| %&gt;
          &lt;%= answers_builder.label :answer %&gt;
          &lt;%= answers_builder.text_box :answer %&gt;
        &lt;% end %&gt;
    &lt;% end %&gt;
    &lt;%= link_to_add_fields 'New', f, :questions %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>This code example works fully for the first instance of Question. The issue occurs when another question is dynamically added to be created; the answer fields are not displayed. I believe this is because they are only built for the first question in the controller. Is there a way to achieve this using nested_attributes?</p>