time_scopes.rb

#
# This module is a collection of named_scope for time column.
# Requires MySQL to work because of usage of MySQL functions.
# But you can easly replace that part to work with another databases.
#
# Example
#
#   class Article < ActiveRecord::Base
#     include TimeScopes[:created_at]
#   end
#
#   Article.year(2010).month(8)   # Gives you all articles created at 2010-08.
#   Article.day_of_week(:monday)  # Gives you all articles created at Monday.
#
module TimeScopes
  def self.[](column)
    Module.new do
      (class << self; self; end).send(:define_method, :included) do |base|
        base.class_eval do
          named_scope :year, lambda { |year|
            { :conditions => ["YEAR(#{column}) = ?", year] } unless year.blank?
          }

          named_scope :month, lambda { |month|
            { :conditions => ["MONTH(#{column}) = ?", month] } unless month.blank?
          }

          named_scope :day, lambda { |day|
            { :conditions => ["DAY(#{column}) = ?", day] } unless day.blank?
          }

          named_scope :day_of_week, lambda { |day_of_week|
            day_of_week = %w(:sunday :monday :tuesday :wednesday :thursday :friday :saturday).index(day_of_week)
            { :conditions => ["DAYOFWEEK(#{column}) = ?", day_of_week] } unless day_of_week.nil?
          }
        end
      end
    end
  end
end