Ruby: combine Date and Time objects into a DateTime

Question

Simple question, but I can\'t find a good or definitive answer. What is the best and most efficient way to combine Ruby Date and Time objects (objects, not

Answer 1

I found this, but it's not as elegant you would hope:

d = Date.new(2012, 8, 29)
t = Time.now
dt = DateTime.new(d.year, d.month, d.day, t.hour, t.min, t.sec, t.zone)

By the way, the ruby Time object also stores a year, month, and day, so you would be throwing that away when you create the DateTime.

Answer 2

If you are using Ruby on Rails, this works great.

I built a method to extend the DateTime class to combine a date and a time. It takes the zone from the date so that it does not end up an hour off with daylight savings time.

Also, for convenience, I like being able to pass in strings as well.

class DateTime
  def self.combine(d, t)
    # pass in a date and time or strings
    d = Date.parse(d) if d.is_a? String 
    t = Time.zone.parse(t) if t.is_a? String
    # + 12 hours to make sure we are in the right zone
    # (eg. PST and PDT switch at 2am)
    zone = (Time.zone.parse(d.strftime("%Y-%m-%d")) + 12.hours ).zone
    new(d.year, d.month, d.day, t.hour, t.min, t.sec, zone)
  end
end

So you can do:

DateTime.combine(3.weeks.ago, "9am")

or

DateTime.combine("2015-3-26", Time.current)

etc...

Answer 3

If using Rails, try any of these:

d = Date.new(2014, 3, 1) 
t = Time.parse("16:30")

dt = d + t.seconds_since_midnight.seconds   
# => ActiveSupport::TimeWithZone

dt = (d + t.seconds_since_midnight.seconds).to_datetime   
# => DateTime

dt = DateTime.new(d.year, d.month, d.day, t.hour, t.min, t.sec)   
# => DateTime

Answer 4

I found another way, I hope this is correct.

 datetojoin=Time.parse(datetime).strftime("%Y-%m-%d")
       timetojoin=Time.parse(time).strftime("%T")          
       joined_datetime = Time.parse(datetojoin +" "+ timetojoin).strftime("%F %T")

Any thoughts? Please share.

Answer 5

Simple:

Date.new(2015, 2, 10).to_datetime + Time.parse("16:30").seconds_since_midnight.seconds

# => Object: Tue, 10 Feb 2015 16:30:00 +0000

You gotta love Ruby!

Answer 6

When using seconds_since_midnight, changes in daylight savings time can lead to unexpected results.

Time.zone = 'America/Chicago'
t  = Time.zone.parse('07:00').seconds_since_midnight.seconds
d1 = Time.zone.parse('2016-11-06').to_date # Fall back
d2 = Time.zone.parse('2016-11-07').to_date # Normal day
d3 = Time.zone.parse('2017-03-12').to_date # Spring forward

d1 + t
#=> Sun, 06 Nov 2016 06:00:00 CST -06:00
d2 + t
#=> Mon, 07 Nov 2016 07:00:00 CST -06:00
d3 + t
#=> Sun, 12 Mar 2017 08:00:00 CDT -05:00

Here's an alternative, similar to @selva-raj's answer above, using string interpolation, strftime, and parse. %F is equal to %Y-%m-%d and %T is equal to %H:%M:%S.

Time.zone = 'America/Chicago'
t = Time.zone.parse('07:00')
d1 = Time.zone.parse('2016-11-06').to_date # Fall back
d2 = Time.zone.parse('2016-11-07').to_date # Normal day
d3 = Time.zone.parse('2017-03-12').to_date # Spring forward

Time.zone.parse("#{d1.strftime('%F')} #{t.strftime('%T')}")
#=> Sun, 06 Nov 2016 07:00:00 CST -06:00
Time.zone.parse("#{d2.strftime('%F')} #{t.strftime('%T')}")
#=> Sun, 07 Nov 2016 07:00:00 CST -06:00
Time.zone.parse("#{d3.strftime('%F')} #{t.strftime('%T')}")
#=> Sun, 12 Mar 2017 07:00:00 CDT -05:00