Convert UTC to local time in Rails 3

问题

I\'m having trouble converting a UTC Time or TimeWithZone to local time in Rails 3.

Say moment is some Time variable in UTC (e.g. moment = Time.now.utc). How do I convert moment to my time zone, taking care of DST (i.e. using EST/EDT)?

More precisely, I\'d like to printout \"Monday March 14, 9 AM\" if the time correspond to this morning 9 AM EDT and \"Monday March 7, 9 AM\" if the time was 9 AM EST last monday.

Hopefully there\'s another way?

Edit: I first thought that \"EDT\" should be a recognized timezone, but \"EDT\" is not an actual timezone, more like the state of a timezone. For instance it would not make any sense to ask for Time.utc(2011,1,1).in_time_zone(\"EDT\"). It is a bit confusing, as \"EST\" is an actual timezone, used in a few places that do not use Daylight savings time and are (UTC-5) yearlong.

回答1:

Rails has its own names. See them with:

rake time:zones:us

You can also run rake time:zones:all for all time zones. To see more zone-related rake tasks: rake -D time

So, to convert to EST, catering for DST automatically:

Time.now.in_time_zone("Eastern Time (US & Canada)")

回答2:

Time#localtime will give you the time in the current time zone of the machine running the code:

> moment = Time.now.utc
  => 2011-03-14 15:15:58 UTC 
> moment.localtime
  => 2011-03-14 08:15:58 -0700

Update: If you want to conver to specific time zones rather than your own timezone, you're on the right track. However, instead of worrying about EST vs EDT, just pass in the general Eastern Time zone -- it will know based on the day whether it is EDT or EST:

> Time.now.utc.in_time_zone("Eastern Time (US & Canada)")
  => Mon, 14 Mar 2011 11:21:05 EDT -04:00 
> (Time.now.utc + 10.months).in_time_zone("Eastern Time (US & Canada)")
  => Sat, 14 Jan 2012 10:21:18 EST -05:00

回答3:

There is actually a nice Gem called local_time by basecamp to do all of that on client side only, I believe:

https://github.com/basecamp/local_time

回答4:

It is easy to configure it using your system local zone, Just in your application.rb add this

config.time_zone = Time.now.zone

Then, rails should show you timestamps in your localtime or you can use something like this instruction to get the localtime

Post.created_at.localtime

回答5:

Don't know why but in my case it doesn't work the way suggested earlier. But it works like this:

Time.now.change(offset: "-3000")

Of course you need to change offset value to yours.

回答6:

If you're actually doing it just because you want to get the user's timezone then all you have to do is change your timezone in you config/applications.rb.

Like this:

Rails, by default, will save your time record in UTC even if you specify the current timezone.