A helper for building scopes that deal with moving windows.

require 'moving_window'

class Review < ActiveRecord::Base
  scope :recent, MovingWindow.scope { 6.months.ago }
end

Review.recent # Returns reviews from the last 6 months.

You can specify an end to the window with an array. The ordering does not matter:

scope :a_while_ago, MovingWindow.scope { [3.months.ago, 6.months.ago] }

By default, created_at is used. If you want to specify a different column:

scope :recently_published, MovingWindow.scope(:published_at) { 6.months.ago }

Dates in the future will also work.

Note: There's no need to worry about invoking the scope with a lambda. The timestamps will be re-evaluated on each call.

You'll find that .scope won't work outside of an active record model. Invoke things manually instead:

window = MovingWindow.new { 6.months.ago }
window.filter(Review, :column => :published_at)

Arel is fully supported:

window.filter(Review.published).limit(5)

You can find all records that lie outside of the moving window by negating it:

scope :not_recent, MovingWindow.scope { 6.months.ago }.not

If you're calling things manually:

window.filter(Review, :negate => true)