UpdateTimestampFieldsToUtc.rb

class UpdateTimestampFieldsToUtc < ActiveRecord::Migration

  cattr_accessor :use_utc
  
  def self.up
    transaction do
      @@use_utc = true
      adjust_models
    end
  end

  def self.down
    transaction do
      @@use_utc = false
      adjust_models
    end
  end
  
  class << self
  
    def adjust_models
      adjust_fields(Task, ['created_at', 'start_at', 'stop_at'])
      adjust_fields(Order, ['created_at'])
      adjust_fields(Project, ['created_at'])
      adjust_fields(User, ['created_at', 'activated_at', 'remember_token_expires_at'])
    end

    def adjust_fields(model, fields)
      # for each of this model's objects
      model.all.each do |obj|
        # build a set of updates
        updates = []
        fields.each do |f|
          # go to either utc or eastern, based on setting of @use_utc
          unless obj.send(f.to_sym).blank?
            # do a direct db update to avoid active record translation to utc!
            interval = @@use_utc ? adjust_to_utc(obj.send(f.to_sym)) : adjust_to_eastern(obj.send(f.to_sym))
            updates << "#{f} = #{f} + '#{interval} hours'::interval"
          end # unless
        end # fields.each
        unless updates.empty?
          sql = "UPDATE #{model.table_name} SET #{updates.join(', ')} WHERE id = #{obj.id};"
          puts sql
          ActiveRecord::Base.connection.execute(sql)
        end
      end # model.each
    end

    def adjust_to_utc(time)
      time.dst? ? 4 : 5
    end
  
    def adjust_to_eastern(time)
      time.dst? ? -4 : -5
    end
  
  end # class << self
end