DateTime.now还是Time.now？

Question

Which of the two should I be using in my Rails application:

DateTime.now or Time.now

Is there any harm in using both in the application?

Can there ever be any differences between the two in case of the above ( now ) example? (On my current system they are both showing the same time)

Answer 1

Use (Date)Time.current instead of (Date)Time.now

Rails extends the Time and DateTime objects, and includes the current property for retrieving the time the Rails environment is set to (default = UTC), as opposed to the server time (Could be anything).

This is critical- You should always be working in UTC time except when converting between timezones for user input or display- but many production systems are not UTC by default. (eg Heroku is set to PST (GMT -8))

See article here

Answer 2

In reference to Time.now (not DateTime.now ):

The object created will be created using the resolution available on your system clock, and so may include fractional seconds.

a = Time.new      #=> Wed Apr 09 08:56:03 CDT 2003
b = Time.new      #=> Wed Apr 09 08:56:03 CDT 2003
a == b            #=> false
"%.6f" % a.to_f   #=> "1049896563.230740"
"%.6f" % b.to_f   #=> "1049896563.231466"

Answer 3

If you want to get the time in the application's time zone, you'll need to call Time.zone.now , so that's what I generally use.

Time.now and DateTime.now will both return a time in the system's time, which often is set to UTC.