Rails does not display error messages on a form in a custom method

I've created a custom method called checkout in my 开发者_开发问答app. I create an order (which is done my adding products to my "cart"), assign it to my client, and then I head to my checkout screen where I confirm the items and enter their customer order number and complete the order (submit).

Everything works great except that it doesn't display error messages. I'm able to display a flash error notice (seen in complete_order method) when things go wrong but it doesn't specify the details like a normal form would. The error messages should appear if the customer order number is not unique for that client.

Below is the custom method (checkout) related code.

Order Model:

validates_uniqueness_of :customer_order_number, :scope => :client_id

Orders_controller:

  def checkout
    @order = current_order
  end

  def complete_order
    @order = current_order

    respond_to do |format|
      if @order.update_attributes(params[:order])
        @order.complete #sets submitted datetime and state to 'complete'
        flash[:notice] = 'Thank you! Your order is being processed.'
        format.html { redirect_to( products_path ) }
        format.xml  { head :ok }
      else
        flash[:error] = 'Please review your items' #added to confirm an error is present
        format.html { redirect_to( checkout_path ) }
        format.xml  { render :xml => @order.errors, :status => :unprocessable_entity }
      end
    end

  end

And the form in the checkout view:

<% form_for @order, :url => { :controller => "orders", :action => "complete_order" } do |f| %>

  <%= f.error_messages %>


    <%= f.text_field :customer_order_number, :label => "Purchase Order Number" %>

    <p>
    <%= f.submit 'Complete Order', :confirm => 'Are you sure?' %> <small> or <%= link_to 'cancel', current_cart_path %></small>
  </p>

<% end %>

Any idea how I can display the specific error messages?

Change redirect_to to render in else condition otherwise checkout method get called again & no error will displayed.

else
     format.html { render :action => 'checkout' }