Ryan Screen Cast Code:

Controller

class ProductsController < ApplicationController
  helper_method :sort_column, :sort_direction

  def index
    @products = Product.order(sort_column + " " + sort_direction)
  end

  # ...

  private

  def sort_column
    Product.column_names.include?(params[:sort]) ? params[:sort] : "name"
  end

  def sort_direction
    %w[asc desc].include?(params[:direction]) ? params[:direction] : "asc"
  end
end

Helper

def sortable(column, title = nil)
  title ||= column.titleize
  css_class = column == sort_column ? "current #{sort_direction}" : nil
  direction = column == sort_column && sort_direction == "asc" ? "desc" : "asc"
  link_to title, {:sort => column, :direction => direction}, {:class => css_class}
end

index.html.erb

<tr>
  <th><%= sortable "name" %></th>
  <th><%= sortable "price" %></th>
  <th><%= sortable "released_at", "Released" %></th>
</tr>

concept

<tr>
  <th class=<%= @selected %> ><%= sortable "name" %></th>
  <th class=<%= @selected %> ><%= sortable "price" %></th>
  <th class=<%= @selected %> ><%= sortable "released_at", "Released" %></th>
</tr>

CSS

.pretty th .current {
  padding-right: 12px;
  background-repeat: no-repeat;
  background-position: right center;
}

.pretty th .asc {
  background-image: url(/images/up_arrow.gif);
}

.pretty th .desc {
  background-image: url(/images/down_arrow.gif);
}

css ruby-on-rails-3