DistroPropaganda/code/rails30/depot_n/db/migrate/20110211000005_combine_items_in_cart.rb

#---
# Excerpted from "Agile Web Development with Rails",
# published by The Pragmatic Bookshelf.
# Copyrights apply to this code. It may not be used to create training material,
# courses, books, articles, and the like. Contact us if you are in doubt.
# We make no guarantees that this code is fit for any purpose.
# Visit http://www.pragmaticprogrammer.com/titles/rails4 for more book information.
#---
#---
# Excerpted from "Agile Web Development with Rails, 4rd Ed.",
# published by The Pragmatic Bookshelf.
# Copyrights apply to this code. It may not be used to create training material, 
# courses, books, articles, and the like. Contact us if you are in doubt.
# We make no guarantees that this code is fit for any purpose. 
# Visit http://www.pragmaticprogrammer.com/titles/rails4 for more book information.
#---
class CombineItemsInCart < ActiveRecord::Migration

  def self.up
    # replace multiple items for a single product in a cart with a single item
    Cart.all.each do |cart|
      # count the number of each product in the cart
      sums = cart.line_items.group(:product_id).sum(:quantity)

      sums.each do |product_id, quantity|
        if quantity > 1
          # remove individual items
          cart.line_items.where(:product_id=>product_id).delete_all

          # replace with a single item
          cart.line_items.create(:product_id=>product_id, :quantity=>quantity)
        end
      end
    end
  end

  def self.down
    # split items with quantity>1 into multiple items
    LineItem.where("quantity>1").each do |line_item|
      # add individual items
      line_item.quantity.times do 
        LineItem.create :cart_id=>line_item.cart_id,
          :product_id=>line_item.product_id, :quantity=>1
      end

      # remove original item
      line_item.destroy
    end
  end
end