gistfile1.rb

class Message < ActiveRecord::Base
  scope :last_two_weeks, -> {
    where(:created_at => (2.weeks.ago..Time.now)) 
  }
  
  scope :for_month, (date) -> {
    where(:created_at => (date.beginning_of_month..date.end_of_month))
  }
  
  def self.sum_word_count
    sum(:word_count)
  end
end

dan.messages.for_month(2.months.ago).sum_word_count

dan.messages.last_two_weeks.sum_word_count

dan.messages.sum_word_count