How to add 3 calendar months to a Time attribute?

Rails
1

I thought this might be easy, but unless I’m missing something it’s not
so
straightforward…

I have a datetime attribute and I want to add n Calendar months to it.
How do I do that?

Thanks in advance,

Matt.

2

Time.now + 3.months

or…

model[:some_date] += 3.months

you’ll need to handle the year boundaries yourself

3

thanks Ian.

I got “NoMethodError: undefined method `months’ for 3:Fixnum” trying to
run that snippet of code (I tried in irb too).

I finally ended up with this. It seems to handle year boundaries, too.
Hopefully someone else will find it useful:

pd = DateTime.new(ParseDate.parsedate(@ad.starts_at.to_s)[0…4])
@ad.ends_at = ea>>(3@ad.listing_period_quarters.to_i)

Cheers,

Matt.

4

Matthew L. wrote:

thanks Ian.

I got “NoMethodError: undefined method `months’ for 3:Fixnum” trying to
run that snippet of code (I tried in irb too).

The months method isn’t part of ruby itself, ActiveSupport adds that
(and a bunch of other helpers), so in a vanilla irb session you will get
that error. In the environment you get with a ruby script/console it
should work fine.
It’s also worth noting that foo + 1.month == foo + 30.days (and that’s
pretty much the way it has to be).

Fred

5

On Thu, Sep 14, 2006 at 11:58:47AM +0100, Matthew L. wrote:

I thought this might be easy, but unless I’m missing something it’s not so
straightforward…

I have a datetime attribute and I want to add n Calendar months to it.
How do I do that?

Thanks in advance,

Using 3 months as an example…

Add 3 months:
time >> 3

Subtract 3 months:
time << 3

Test with:
ruby -r date -e ‘puts (DateTime.now() >> 3).strftime(“%m/%d/%Y”)’

Don’t try using “3.months”, as it’ll add 90 days which is guaranteed to
be incorrect. It also has issues since 3.months simply returns the
integer 7776000, which is the number of seconds in 90 days
(606024303). If you try adding that to a “Date” value instead of a
“DateTime” value, you’ll get something really wacky since “Date” objects
view integers as a number of days rather than seconds. “>>” and “<<”
work the same for both Date’s and DateTime’s.

Date/time arithmetic is awesomely easy in Ruby, just read up on the Date
class at RDoc Documentation.

Michael

Michael Darrin Chaney
[email protected]
http://www.michaelchaney.com/

6

Using 3 months as an example…

Add 3 months:
time >> 3

Subtract 3 months:
time << 3

Test with:
ruby -r date -e ‘puts (DateTime.now() >> 3).strftime(“%m/%d/%Y”)’

That was just what I was looking for.

Date/time arithmetic is awesomely easy in Ruby, just read up on the Date
class at RDoc Documentation.

I had a feeling it would be, hence the question! I did look around the
RoR api docs but didn’t see anything which looked useful. I noticed
months_since etc after someone pointed it out to me, and I am using that
in Rails, but knowing this will be handy outside of Rails, too!

I’m pretty new to Ruby and it impresses me more every day.

Thanks very much!

Matt.

7

I think what you’re looking for is:

time.months_since(3)

see following for all date calculations:
http://api.rubyonrails.org/classes/ActiveSupport/CoreExtensions/Time/Calculations.html

c.

Matthew L. wrote:

I thought this might be easy, but unless I’m missing something it’s not
so
straightforward…

I have a datetime attribute and I want to add n Calendar months to it.
How do I do that?

Thanks in advance,

Matt.