No route matches {:action=>"show", :controller=>"carts"} missing required keys: [:id]


I follow the Agile Web development book.

Now as a extra challenge I try to make the card visible on a seperate page.

So I made this link :

  • <%= link_to ' Card'.html_safe, cart_path %>
  • But now I see the above error message.

    When I do card_path (:id) I see a message that there is no card with the id of id.


    What is the url you’re using to show this on a separate page ?

    if its in the pattern of “/cards/:id/something” then you dont have to provide the card path as rails picks up @card object to build the path or you’ll have to pass the card variable inside the path method.


    <% @cards.each do |card| %>

  • <%= link_to ' Card'.html_safe, cart_path(card) %>
  • <% end %>

    This way, rails would know “which” exact card this link should take them to.


    It’s is the form of /cards/:id

    I tried

  • <%= link_to ' Card'.html_safe, cart_path(cart) %>
  • <%= link_to ' Card'.html_safe, cart_path(card) %>
  • but on both I see this message :

    undefined local variable or method `cart'
    undefined local variable or method `card'


    If you’re on “/cards/:id”, then look at your cards_controller.rb , you’d see @card defined , hence you should use

  • <%= link_to ‘ Card’.html_safe, cart_path(@card) %>
  • But why would you goto to the show page ( /cards/:id/ ) when you’re already on the page ? regarding the cart, You have to follow the same procedure. define @cart in the controller/action and use it like this

  • <%= link_to ' Card'.html_safe, cart_path(@cart) %>
  • If you can give more info on what you’re trying to do (app structure) , We can help you a bit better :slight_smile:

    PS: i haven’t read the book



    Im at the home page and I want to make a link to /card/:id

    According to rake routes I have to use cart_path.

    The carts route looks like this :

    class CartsController < ApplicationController

    before_action :set_cart, only: [:show, :edit, :update, :destroy]

    def index @carts = Cart.all end

    def show end

    def new @cart = end

    Which uses this file :

    module CurrentCart extend ActiveSupport::Concern

    def set_cart
        @cart = Cart.find(session[:cart_id])
        rescue ActiveRecord::RecordNotFound
        @cart = Cart.create
        session[:cart_id] =


    So I have to figure out how to make the id of the card avaible on the url.