item.rb

class Item
  def self.find_each(params = {})
    return enum_for(:find_each) unless block_given?

    page = nil
    while page.nil? || page.current_page < page.total_pages
      if page.nil?
        page = all params
      else
        page = all params.merge(page: page.current_page + 1)
      end

      page.each do |item|
        yield item
      end
    end
  end

  def self.all(params = {})
   # snip
  end
end

# yields as it goes, retrieving pages as needed behind the scenes
Item.find_each do |item|
 puts item.name
end

# only retrieves the first two pages
# Ruby 1.9 doesn't do lazy map or reduce, I think?
Item.find_each.take(75).map(&:price).reduce(:+)

# only retrieves the first two pages
# Ruby 2 allows this?
Item.find_each.map(&:price).reduce(:+).take(75)