On 11/08/2016 11:24 PM, George Neuner wrote:
[...]
- I need to turn the UTC datetimes on all the results back into local
times with the right time zone
Does the following do what you want?
(require srfi/19)
;; date-at-tz : Date Integer -> Date
;; Returns date of equivalent instant in given timezone.
(define (date-at-tz d tz)
(let ([t (date->time-utc d)])
(time-utc->date t tz)))
(define fmt "~Y-~m-~d ~H:~M:~S~z")
(define s1 "2016-11-09 01:12:00Z")
(define d1 (string->date s1 fmt))
(define d2 (date-at-tz d1 (* -5 60 60)))
(date->string d1 fmt)
;; => "2016-11-09 01:23:00Z"
(date->string d2 fmt)
;; => "2016-11-08 20:23:00-0500"
(equal? (date->time-utc d1) (date->time-utc d2))
;; => #t
Another option is to let PostgreSQL do it for you using AT TIME ZONE (or
the timezone function):
select ('2016-11-09 01:23:00Z'::timestamptz)
at time zone 'us/eastern';
=> 2016-11-08 20:23:00
But beware that PostgreSQL interprets numerical timezones backwards
(sometimes?) (see
https://www.postgresql.org/message-id/20151021034109.3017....@wrigleys.postgresql.org).
I've read that thread and the docs and I still can't make sense of it.
Ryan
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