Simple pagination

article.rb

class Article < ActiveRecord::Base
  extend Pagination

  self.per_page = 20
end

# Article.page(params[:page])
# Article.page(params[:page]).per_page(params[:per_page])
# Article.paginate(page: params[:page], per_page: params[:per_page])

pagination.rb

module Pagination
  attr_writer :per_page

  def page(page)
    set_page page
    build_query
  end

  def per_page(per_page)
    set_per_page per_page
    build_query
  end

  def paginate(options = {})
    extract_options options
    build_query
  end

private

  def build_query
    return all unless @page && @per_page

    all.tap do |rel|
      rel.limit  = @per_page
      rel.offset = @per_page * (@page - 1)
    end
  end

  def extract_options(options)
    set_page(options[:page]) if options.has_key?(:page)
    set_per_page(options[:per_page]) if options.has_key?(:per_page)
  end

  def set_page(page)
    @page = page ? page.to_i : 1
  end

  def set_per_page(per_page)
    @per_page = per_page.to_i
  end
end