Q:

rails routing - path issue

i've been scratching my head over this, but i keep getting this error

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

In my simple minded logic whenever i go for category_product_path and pass in the category, i should have the list of products within that category.  But i'm probably missing something.  This is my view file ... where i've tried several stuff without success
<% @products.each do |product| %>
    <tr>
        <td><%= link_to product.name, category_product_path(@category) %></td>
        <td><%= product.category_id %></td>
        <td><%= number_to_euro(product.price) %></td>
        <td><%= product.stock %></td>
        <td><%= image_tag(product.image.thumb) %></td>
        <br>
        </tr>
<% end %>

This is my routes
namespace :admin do
  resources :categories
  resources :products
  resources :orders
end
resources :categories, only: [:index, :show] do
  resources :products, only: [:index, :show]
end
resources :orders, only: [:new, :create]

And what i assume to be the problem, somewhere in the controllers (not the ones in the admin folder)
class CategoriesController < ApplicationController    
    before_action :set_category, only: [:show]
    def index
      @categories = Category.all
    end

    def show
      @products = @category.products
    end

    private

    def set_category
      @category = Category.find(params[:id])
    end
end

class ProductsController < ApplicationController
    before_action :set_product, only:[:show]
    def index
        @products = Product.all
    end

    def show
    end

    private

    def set_product
      @product = Product.find(params[:id])
    end
end

A:

You'll need to add both @category and product variables to your route:
<%= link_to product.name, category_product_path(@category, product) %>

--
Update
I don't know where you're calling your view, but if I'm right in thinking it's categories/:category_id/products/, then @category isn't being set:
#app/controllers/products_controller.rb
class ProductsController < ApplicationController
   def index
      @category = Category.find params[:category_id]
      @products = @category.products
   end
end 

If you're not doing this, it does suggest your @category value is not present.  To test this, manually insert a @category value:
<%= link_to product.name, category_product_path("2", product) %>

Tip: Multiple resource declarations
#config/routes.rb
namespace :admin do
  #needs a root
  resources :categories, :products, :orders
end
resources :categories, only: [:index, :show] do
  resources :products, only: [:index, :show]
end
resources :orders, only: [:new, :create]

