Rails DateTime object isn't what I expect

I'm a Java developer who is very new to Ruby so if this question is a little too basic, please go easy on me. :) I'm here to learn if someone can point me in the开发者_Go百科 right direction.

I'm writing an application that deals with times and will need to take time zones into account. I was curious what Ruby offers for dealing with timezones and I found that Rails provides a DateTime class that should do what I need. http://api.rubyonrails.org/classes/DateTime.html#method-i-in_time_zone

However, when I create a DateTime, it doesn't seem to have the methods I expect. Can someone explain what is going on here? Here is what I'm seeing in irb:

>> dt = DateTime.now
NameError: uninitialized constant DateTime
    from (irb):1
>> require 'rails'
=> true
>> dt = DateTime.now
=> #<DateTime: 212158799144191849/86400000000,-1/4,2299161>
>> dt.respond_to? "in_time_zone"
=> false

Since DateTime isn't defined until I require rails, I assumed I was using the Rails DateTime but it doesn't seem to have the methods I'm expecting based on the documentation.

---

DateTime is a core class, and part of Date. It is available if you require 'date' in your code; You don't have to use Rails to access it.

require 'date'

asdf = DateTime.parse(`date`)
asdf # => #<DateTime: 2010-12-10T21:41:59-07:00 (212158802519/86400,-7/24,2299161)>
asdf.class # => DateTime
asdf.to_s # => "2010-12-10T21:41:59-07:00"

The class you're after is part of ActiveSupport, which is part of Rails, but you don't have to load Rails to access it:

require 'active_support/all'
asdf.in_time_zone # => Fri, 10 Dec 2010 21:43:42 -0700

or

require 'active_support/core_ext'
asdf.in_time_zone # => Fri, 10 Dec 2010 21:59:48 -0700

Ruby's Time class has good support for timezones also, so you might want to get familiar with it too.

---

You don't need whole Rails stack for timezone support. You can install and use just active_support. But you can as well check out tzinfo gem.