A Time object being converted to epoch and back loses its milliseconds in Ruby

Question

I seem to have found a bug in Ruby, but I'm not sure so I'm posting it here.

I have a Rails app that fetches the latest objects after a given timestamp, which is the timestamp of the last object being shown on the page.

But for some reason it was always returning the last object duplicated. After a while, we decided to convert it to epoch, but it didn't work.

After trying to find where the issue might is, I've come up with the given code:

require 'date'
DateTime.strptime("1358895408.915", "%s").strftime("%s")
# => "1358895408"

Isn't this supposed to work? Am I missing something? How can I safely parse time and keep the milliseconds intact?

sawa · Accepted Answer · 2013-01-23T02:17:32.033

2

(Edited under suggestion following Andrew Marshall)

Use Time.at. That will preserve milliseconds. It takes a numeric instead of a string.

Time.at(BigDecimal.new('1358895408.915'))
.strftime("%s.%L")
# => "1358895408.915"

edited Jan 23 '13 at 02:17

answered Jan 23 '13 at 01:42

sawa

1

Passing a BigDecimal (e.g. `Time.at(BigDecimal.new('1358895408.915'))`) avoids the potential for floating-point related precision issues. – Andrew Marshall Jan 23 '13 at 01:47
1

Being picky: `Time.at` takes any Numeric, not just Float. (+1 btw) – Andrew Marshall Jan 23 '13 at 02:07

1 Answers1