Problems with routing

I have an application that has one purchase_order for each purchase_request.

My models are set up like so

purchase_order.rb

...
belongs_to :purchase_request
...

purchase_request.rb

...
has_one :purchase_order
...

My routes are set up like so:

routes.rb

  resources :purchase_requests do
    :purchase_orders
  end

and in my view I link to it like so:

<%= link_to "Purchase Order", new_purchase_request_purchase_order_path(@purchase_request) %>

and in my form I have:

 <%= f.hidden_field :purchase_request %>

but it is not loading the id of the purchase_request. Any help would be great

I am not sure if this is the proper way to do it but what I did:

in the purchase_orders_controller I placed:

...
def new
@purchase_request = PurchaseRequest.find(params[:purchase_request_id])
...

then in the new view i did:

<%= render 'form', :purchase_request_id=>@purchase_request.id %>

and last but not least, I put this in my _form partial:

<%= f.hidden_field :purchase_request_id, :value=>purchase_request_id %>