date_formats.yml

---
us: %m/%d/%Y

gistfile1.rb

Date::DATE_FORMATS.merge!(YAML.load_file(Rails.root.join('config', 'date_formats.yml')))

class String
  def to_time(format = :db)
    Time.strptime(self, Date::DATE_FORMATS[format])
  end

  def to_date(format = :db)
    Time.strptime(self, Date::DATE_FORMATS[format]).to_date
  end
end

class Time
  def to_s(format = nil)
    return super unless format
    strftime(Date::DATE_FORMATS[format])
  end
end