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Kris Roberts
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Question Kris Roberts · Dec 10, 2023

Converting $H to UTC for a timezone that is not local (Object Script)

#InterSystems IRIS

Working on a project where we have a web browser that we have to determine a pickup date/time for a pharmacy in a different time zones.

We store the different time zones with their Daylight and Standard offsets.

We have a object script method that figures out the the pickup date/time for a particular pharmacy in their local time zone but the data is being returned in the $H format.   

We now need to return it in a UTC format.  I see different methods but don't see a method that will change the $H into a UTC for a different timezone otherwise than the local timezone.  

I know I can figure a way around it but I was wondering if anyone has found that Intersystems has a method that will do it for you?

Thanks,

Kris Roberts

Product version: IRIS 2023.1
$ZV: IRIS for Windows (x86-64) 2023.1 (Build 229U) Fri Apr 14 2023 17:17:41 EDT
Discussion (16)2
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Comments

Dmitry Maslennikov · Dec 11, 2023

$Horolog itself does not contain information about timezone, it's just date and time

if you need to make it to another timezone, you can just add or subtract difference

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Kris Roberts  Dec 11, 2023 to Rich Taylor

I will log look the documentation.
Thanks

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Kris Roberts  Dec 12, 2023 to Rich Taylor

One more question Rich,

I tried reading the %Libraray.PosixTime class information.  I thought that the PosixTime was the days in seconds since Jan 1, 1970 but I think I am missing something.  The PosixTime is in seconds so I was thinking I could....

  • take a time stamp and convert it to a PosixTime
  • an then for an Timezone offset (for example America/New_York would be -05:00) convert it to seconds  -1800
  • add the -1800 to the PosixTime
  • an then convert PosixTime to time stamp - shouldn't the time stamp show a lot more of a difference?  
  • and then convert the PosixTime back to a time stamp and shouldn't it show the timestamp a lot less  than 18 seconds?

    see below 

Starting a cold or something so my mind might not be thinking clearly.

Thanks

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Kris Roberts  Dec 11, 2023 to Dmitry Maslennikov

Correct $H does not have a timezone, however I didn't explain it well that when we figure out the pickup date/time for a pharmacy we would have the timeszone the pharmacy resides in.
So if we figure out the pickup date/time in the $H I then need to convert it to a UTC but for a particular timezone not the locale timezone.
Thanks,

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Robert Cemper · Dec 11, 2023

Your time zone is taken from your settings in the underlying operating system

$ZTZ shows the offset from UTC. You can set it to whatever you need.
but ATTENTION  this affects $H for the whole IRIS instance !!!
take a serious look into documentation on mostly not wanted the side effects

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Alexey Maslov  Dec 11, 2023 to Robert Cemper

Robert, it sounds strange, but... Setting the Time Zone

You can use $ZTIMEZONE to set the time zone used by the current InterSystems IRIS process. Setting $ZTIMEZONE does not change the default InterSystems IRIS time zone or your computer’s time zone setting.

IMHO, $ztimezone setting is dangerous not for its system-wide effect (which it hasn't) but mostly due to its exclusions and anomalies, despite they are accurately listed in docs.

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Robert Cemper  Dec 11, 2023 to Alexey Maslov

Ah, some improvements.
I personally always used UTC since the introduction of ENSEMBLE  (ages back)  

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Kris Roberts  Dec 11, 2023 to Alexey Maslov

Ok.  I will look at that.

Thanks

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Kris Roberts  Dec 11, 2023 to Robert Cemper

Thanks I can't use the $ZTZ to change the UTC.  The server is going to have traffic from many different locations so can't change the server setup.

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Julius Kavay  Dec 11, 2023 to Kris Roberts

You can change the Timezone system variable

//  for example EST (Eastern Standard Time, 5 hours behind UTC)
    set $ztz = 300
//  you can even consider daylight saving
//  for example CET (Central European Time, 1 hour ahead of UTC)
#define DSTOFFSET	-60
#; -60=CET, 300=EST
#define LOCALZONE   -60
    set $ztz = $$$LOCALZONE+$s($system.Util.IsDST():$$$DSTOFFSET,1:0)

Setting $ZTZ affects the current job only (the job, which sets $ztz), so there is no danger for other processes.

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Alexey Maslov  Dec 12, 2023 to Julius Kavay

Setting $ZTZ affects the current job only (the job, which sets $ztz), so there is no danger for other processes

What about REST services or web apps? Isn't there one process possibly serving several clients' requests?

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Julius Kavay  Dec 12, 2023 to Alexey Maslov

Shouldn't be a problem, $ZTZ isn't the only thing you can change.

Whatever value or setting you change, $namespace, $zeof, $horolog, etc. you have to consider a simple rule, if you change things (which can be used by subsequent routines, methods, etc.) for your own use, then after using them, you have to restore them to their original value. That's all.

YouRESTorWHATEVERmethod()
{
  set oldZTZ=$ztz
  set $ztz=<your preferred value>
  ...
  set $ztz=oldZTZ
  return
}
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Kris Roberts  Dec 12, 2023 to Julius Kavay

Good to thought.

Thanks

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