datetime.to_formatted_s(:db) # => "2007-12-04 00:00:00"
datetime.to_formatted_s(:short) # => "04 Dec 00:00"
datetime.to_formatted_s(:long) # => "December 04, 2007 00:00"
datetime.to_formatted_s(:long_ordinal) # => "December 4th, 2007 00:00"
datetime.to_formatted_s(:rfc822) # => "Tue, 04 Dec 2007 00:00:00 +0000"
datetime.to_formatted_s(:iso8601) # => "2007-12-04T00:00:00+00:00"