Need HELP with 340 RailsCast

app datatables products_datatable.rb

class ProductsDatatable
  delegate :params, :h, :link_to, :number_to_currency, to: :@view

  def initialize(view)
    @view = view
  end

  def as_json(options = {})
    {
      sEcho: params[:sEcho].to_i,
      iTotalRecords: Product.count,
      iTotalDisplayRecords: products.total_entries,
      aaData: data
    }
  end

private

  def data
    products.map do |product|
      [
        link_to(product.name, product),
        h(product.category),
        h(product.released_on.strftime("%B %e, %Y")),
        number_to_currency(product.price)
      ]
    end
  end

  def products
    @products ||= fetch_products
  end

  def fetch_products
    products = Product.order("#{sort_column} #{sort_direction}")
    products = products.page(page).per_page(per_page)
    if params[:sSearch].present?
      products = products.where("name like :search or category like :search", search: "%#{params[:sSearch]}%")
    end
    products
  end

  def page
    params[:iDisplayStart].to_i/per_page + 1
  end

  def per_page
    params[:iDisplayLength].to_i > 0 ? params[:iDisplayLength].to_i : 10
  end

  def sort_column
    columns = %w[name category released_on price]
    columns[params[:iSortCol_0].to_i]
  end

  def sort_direction
    params[:sSortDir_0] == "desc" ? "desc" : "asc"
  end
end

app controllers products_controller.rb

class ProductsController < ApplicationController
  def index
    respond_to do |format|
      format.html
      format.json { render json: ProductsDatatable.new(view_context) }
    end
  end

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

app views products index.html.erb

<h1>Products</h1>

<table id="products" class="display" data-source="<%= products_url(format: "json") %>">
  <thead>
    <tr>
      <th>Product Name</th>
      <th>Category</th>
      <th>Release Date</th>
      <th>Price</th>
    </tr>
  </thead>
  <tbody>
  </tbody>
</table>