Как отобразить изображение в индексном режиме

Я использую carrierwave и пытаюсь отображать изображения продуктов в индексном режиме. Это мои модели, контроллеры и представления

product.rb

 class Product < ActiveRecord::Base
   has_many :order_items
   belongs_to :category, required: false
   has_many :product_attachments
   accepts_nested_attributes_for :product_attachments

   mount_uploader :image, ImageUploader
   default_scope { where(active: true) }
end

product_attachment.rb

   class ProductAttachment < ApplicationRecord
     mount_uploader :image, ImageUploader
     belongs_to :product
   end

products_controller.rb (извлечение)

class ProductsController < ApplicationController
  def index
  @products = Product.all
  @order_item = current_order.order_items.new
end


def show
  @product = Product.find(params[:id])
  @product_attachments = @product.product_attachments.all
end

def new
  @product = Product.new
  @product_attachment = @product.product_attachments.build
  @categories = Category.all.map{|c| [ c.name, c.id ] }
end

def create
  @product = Product.new(product_params)
  @product.category_id = params[:category_id] 

  respond_to do |format|
  if @product.save
    params[:product_attachments]['image'].each do |a|
      @product_attachment = @product.product_attachments.create!(:image => a,     :product_id => @product.id)
    end
    format.html { redirect_to @product, notice: 'Product was successfully created.' }
  else
    format.html { render action: 'new' }
   end
  end
end

private
  def product_params
    params.require(:product).permit(:name,:price, :active,  :description, product_attachments_attributes: 
[:id, :product_id, :image], category_attributes: [:category_id, :category])
   end
end

index.html.erb

<div class = "row">
  <div class = "col-xs-offset-1 ">
   <% @products.each do |product| %>
     <%= render "product_row", product: product, order_item: @order_item %>
   <% end %>
</div>

_product_row.html.erb

<div class = "well">

  <div class = "row">

  <div class = "container-fluid row">
  <div class = "col-md-5 col-lg-5 col-sm-5 col-xs-5 binder">
    <br><%= image_tag product.image_url.to_s %><br><br>
 </div>
  <div class = "col-md-4 col-lg-4 col-sm-4 col-xs-4 binder">
    <h4 class = "text-left"><%= product.name.split.map(&:capitalize).join(' ') %> </h4>
    <h4 class = "text-left"><span style = "color: green"><%= number_to_currency(product.price, :unit => "€") %></span></h4>
    <h4><%= link_to Category.find(product.category_id).name, category_path(product.category_id) %></h4>
    <h6 class = "text-left"><%= link_to 'Delete', product_path(product), method: :delete,
          data: { confirm: 'Are you sure?' } %></h6><br><br>
  </div>

 <div class = "col-md-3 col-lg-3 col-sm-3 col-xs-3 binder">

  <%= form_for order_item, remote: true do |f| %>
    <div class = "input-group">
      <%= f.number_field :quantity, value: 1, class: "form-control", min: 1 %>
      <div class = "input-group-btn">
        <%= f.hidden_field :product_id, value: product.id %>
        <%= f.submit "Add to Cart", class: "btn btn-primary text-right" %>
      </div>
    </div>
  <% end %>
 </div>
 </div>

 </div>
</div>

С <%= image_tag product.image_url.to_s %> образ не появляется. Когда я меняю его на <%= image_tag product_attachments.first.image_url.to_s %>, я получаю следующую ошибку:

 undefined local variable or method `product_attachments' for #<#<Class:0x00007f28544ccc68>:0x00007f285dd3aab8>

Я новичок в Ruby и не знаю, что делаю не так и как это исправить. Любая помощь будет оценена по достоинству. Я использую Ruby версии 2.5.1 и rails 5.2.0 на ubuntu.