How do I sum up records within Rails 3?

Question

I have an ItemsSold model which has the total number of magazines, books, videos, greeting_cards, pens sold for a single day. How do I elegantly return an array with the weekly sold totals for each item for the last arbitrary number of weeks?

I have a model file:

#items_sold.rb
class ItemsSold < ActiveRecord::Base
    attr_accessible :magazines, :books, :videos, :greeting_cards, :pens, :sold_date

end

My table is defined as follows:

t.integer :magazines
t.integer :books
t.integer :videos
t.integer :greeting_cards
t.integer :pens
t.datetime :sold_date

Also, is it possible to return monthly totals for the last year, too?

Answer 1

See ActiveRecord::Calculations#sum

by_week = (1...10).inject({}) do |wh, weeks_ago|
  startat = weeks_ago.weeks.ago
  endat = (weeks_ago - 1).weeks.ago
  wh[weeks_ago] = [:magazines, :books, :videos, :greeting_cards, :pens].inject({}) do |sh, attr|
    sh[attr] = ItemsSold.where("sold_date > ? and sold_date <= ?", startat, endat).sum(attr.to_s)
    sh
  end
  wh
end

That will return a hash like {1 => {:magazines => 5, :books => 33, ...}, 2 => {{:magazines => 13, :books => 28, ...}}, ...}, where each key is a week number (1 for this past week, 2 for two weeks ago, etc..) and the value is another hash with the sums.