Routing Error No route matches {:action=>"show"

Question

I only have 2 weeks learning ruby on rails, in my app the users can register their cars, from their profile (code below) the app sent to the registration cars page,

<div class="container">
        <fieldset>
            <h1><%= @user.email %></h1>
             <br> 
             <h2>now you are able to...</h2>
             <br>
             <ul>
                <li>
                    <strong>new car registration: </strong>
                    <%= link_to "new car", new_user_car_path(current_user)%>
                </li>
            </ul>
        </fieldset>
    </div>

it works before but i don't know what i did that now it show this:

Routing Error

No route matches {:action=>"show", :user_id=>#<User id: 27, email: "[email protected]", encrypted_password: "$2a$10$EZtvPWiXgMfUlAqvuvGAzODMaas/y4rGkJPKJtg4PnC6...", reset_password_token: nil, reset_password_sent_at: nil, remember_created_at: nil, sign_in_count: 1, current_sign_in_at: "2012-07-24 19:07:54", last_sign_in_at: "2012-07-24 19:07:54", current_sign_in_ip: "127.0.0.1", last_sign_in_ip: "127.0.0.1", name: nil, created_at: "2012-07-24 19:07:54", updated_at: "2012-07-24 19:07:54">, :controller=>"cars"}

Try running rake routes for more information on available routes.

also I put my carsController

class CarsController < ApplicationController
  def new
    @car = Car.new
  end

  def create
    @car = current_user.Car.new(params[:car])
    if @car.save
      flash[:notice] = "new car created success"
      #redirect_to current_user, :flash => { :success => "car created!" }
    else
      #redirect_to new_user_car_path, 
      flash[:notice] = "sorry try again"
    end
  end

  def index
    @car=Car.all
  end

  def show
   @car = current_user.car.find(params[:id])
   #@car = Car.find(params[:id])
   #redirect_to @user
  end
end

and my routes.rb

Estaciones::Application.routes.draw do
root :to => "static_pages#home"
match '/contact', :to=>'static_pages#contact'
match '/about', :to=>'static_pages#about'
devise_for :users
resources :users do
resources :cars
end

my rake routes:

root        /                                       static_pages#home
             contact        /contact(.:format)                      static_pages#contact
               about        /about(.:format)                        static_pages#about
    new_user_session GET    /users/sign_in(.:format)                devise/sessions#new
        user_session POST   /users/sign_in(.:format)                 devise/sessions#create
destroy_user_session DELETE /users/sign_out(.:format)               devise/sessions#destroy
       user_password POST   /users/password(.:format)               devise/passwords#create
   new_user_password GET    /users/password/new(.:format)           devise/passwords#new
  edit_user_password GET    /users/password/edit(.:format)          devise/passwords#edit
                     PUT    /users/password(.:format)               devise/passwords#update
cancel_user_registration GET    /users/cancel(.:format)                 devise/registrations#cancel
   user_registration POST   /users(.:format)                        devise/registrations#create
 new_user_registration GET    /users/sign_up(.:format)                devise/registrations#new
edit_user_registration GET    /users/edit(.:format)                   devise/registrations#edit
                     PUT    /users(.:format)                        devise/registrations#update
                     DELETE /users(.:format)                        devise/registrations#destroy
           user_cars GET    /users/:user_id/cars(.:format)          cars#index
                     POST   /users/:user_id/cars(.:format)          cars#create
        new_user_car GET    /users/:user_id/cars/new(.:format)      cars#new
       edit_user_car GET    /users/:user_id/cars/:id/edit(.:format) cars#edit
            user_car GET    /users/:user_id/cars/:id(.:format)      cars#show
                     PUT    /users/:user_id/cars/:id(.:format)      cars#update
                     DELETE /users/:user_id/cars/:id(.:format)      cars#destroy
               users GET    /users(.:format)                        users#index
                     POST   /users(.:format)                        users#create
            new_user GET    /users/new(.:format)                    users#new
           edit_user GET    /users/:id/edit(.:format)               users#edit
                user GET    /users/:id(.:format)                    users#show
                     PUT    /users/:id(.:format)                    users#update
                     DELETE /users/:id(.:format)                    users#destroy

this is the new.html.erb for new cars

<div class="container">
<h2>new car registration</h2>

<%= form_for(:users, :url => user_car_path(current_user)) do |f| %>
  <div><%= f.label :brand %><br />
    <%= f.text_field :brand %></div>

    <div><%= f.label :color %><br />
    <%= f.text_field :color %></div>

    <div><%= f.label :model %><br />
    <%= f.text_field :model %></div>

  <div><%= f.label :year %><br />
  <%= f.text_field :year %></div>

    <div><%= f.submit "new car",:class => "btn btn-primary" %></div>
<% end %>

Answer 1

<%= link_to "new car", new_user_car_path(current_user)%>

should be ok given your route

     new_user_car GET    /users/:user_id/cars/new(.:format)      cars#new

but the error says that a car#show (not new!) is missing, so maybe look for that.

When is the error exactly thrown?

ADDITION: now that you've posted the form,

I think the line producing the error is

<%= form_for(:users, :url => user_car_path(current_user)) do |f| %>

because user_car_path needs both a user and a car - so you would need

user_car_path(current_user,@car)

I've used just this in my form:

<%= form_for ([@user,@car]) do |f| %>

but the bottom line is, every time you're referencing a car, you need also the enclosing user reference.