title: form_for with module and namespace
body: <p>I have the follow models in Finance module:</p>
  
  <pre><code>class Finance::BillRec &lt; ActiveRecord::Base
    ...
    has_many :bill_rec_offs, :dependent =&gt; :destroy
    ...
  end
  
  class Finance::BillRecOff &lt; ActiveRecord::Base
    ...
    belongs_to :bill_rec
    ...
  end
  </code></pre>
  
  <p>I'm doing this on my form_for:</p>
  
  <pre><code>&lt;%= form_for([@bill_rec, @bill_rec_off]) do |f| %&gt;
    ...
  &lt;% end %&gt;
  </code></pre>
  
  <p>routes.rb</p>
  
  <pre><code>namespace :finance do
    resources :bill_recs do
      resources :bill_rec_offs
    end
  end
  </code></pre>
  
  <p>And the error:</p>
  
  <pre><code>undefined method `finance_bill_rec_finance_bill_rec_offs_path' for #&lt;#&lt;Class:0x000000070757e0&gt;:0x0000000708bec8&gt;
  </code></pre>
  
  <p>However, the route finance_bill_rec_bill_rec_off_path(@bill_rec_off) works well.</p>
  
  <p>How can I do on a form_for with namespace and nested routes with module?</p>