Convert to/from DateTime and Time in Ruby

Question

How do you convert between a DateTime and a Time object in Ruby?

Answer 1

You'll need two slightly different conversions.

To convert from Time to DateTime you can amend the Time class as follows:

require 'date'
class Time
  def to_datetime
    # Convert seconds + microseconds into a fractional number of seconds
    seconds = sec + Rational(usec, 10**6)

    # Convert a UTC offset measured in minutes to one measured in a
    # fraction of a day.
    offset = Rational(utc_offset, 60 * 60 * 24)
    DateTime.new(year, month, day, hour, min, seconds, offset)
  end
end

Similar adjustments to Date will let you convert DateTime to Time .

class Date
  def to_gm_time
    to_time(new_offset, :gm)
  end

  def to_local_time
    to_time(new_offset(DateTime.now.offset-offset), :local)
  end

  private
  def to_time(dest, method)
    #Convert a fraction of a day to a number of microseconds
    usec = (dest.sec_fraction * 60 * 60 * 24 * (10**6)).to_i
    Time.send(method, dest.year, dest.month, dest.day, dest.hour, dest.min,
              dest.sec, usec)
  end
end

Note that you have to choose between local time and GM/UTC time.

Both the above code snippits are taken from O'Reilly's Ruby Cookbook. Their code reuse policy permits this.

Answer 2

This isn't really that hard.

require 'date'

date_time = DateTime.now
# #<DateTime: blah>
date_time.to_time
# #<Time: blah>

time = Time.now
# #<Time: blah>
time.to_datetime
# #<DateTime: blah>

Answer 3

require 'time'
require 'date'

t = Time.now
d = DateTime.now

dd = DateTime.parse(t.to_s)
tt = Time.parse(d.to_s)

Answer 4

Can't add comment at proper location, this will have to do.

@Gordon Wilson:

Works for me with the following caveat: to_local_time() returns the utc time instead. I believe the 'DateTime.now.offset-offset' is overkill, since you are specifying ':local' already. The two terms cancel each other out.

Answer 5

Unfortunately, the DateTime.to_time, Time.to_datetime and Time.parse functions don't retain the timezone info. Everything is converted to local timezone during conversion. Date arithmetics still work but you won't be able to display the dates with their original timezones. That context information is often important. For example, if I want to see transactions performed during business hours in New York I probably prefer to see them displayed in their original timezones, not my local timezone in Australia (which 12 hrs ahead of New York).

The conversion methods below do keep that tz info.

For Ruby 1.8, look at Gordon Wilson's answer. It's from the good old reliable Ruby Cookbook.

For Ruby 1.9, it's slightly easier.

require 'date'

# Create a date in some foreign time zone (middle of the Atlantic)
d = DateTime.new(2010,01,01, 10,00,00, Rational(-2, 24))
puts d

# Convert DateTime to Time, keeping the original timezone
t = Time.new(d.year, d.month, d.day, d.hour, d.min, d.sec, d.zone)
puts t

# Convert Time to DateTime, keeping the original timezone
d = DateTime.new(t.year, t.month, t.day, t.hour, t.min, t.sec, Rational(t.gmt_offset / 3600, 24))
puts d

This prints the following

2010-01-01T10:00:00-02:00
2010-01-01 10:00:00 -0200
2010-01-01T10:00:00-02:00

The full original DateTime info including timezone is kept.