Datatypes For Handling Date and Time in Persistent Classes

Question

Question

Evgeny Shvarov · Apr 13, 2018

#Object Data Model #Caché

Hi, Community!

When I introduce a field to a persistent class to manage date/time what datatype should I prefer?

%Date or %TimeStamp? And why?

Discussion (12)2

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Vitaliy Serdtsev · Apr 14, 2018

%PosixTime

%PosixTime is preferable to %TimeStamp, because it takes up less disk space and memory than the %TimeStamp data type and provides better performance than %TimeStamp.^proof

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score 2 · Answer 1 · 2018-04-13T17:57:21-04:00

Robert Cemper · Apr 13, 2018

%Date is just handling +$h, no time (that would be %Time)
%Timestamp is the real object equivalent of $h

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score 0 · Answer 2 · 2018-04-14T08:24:04-04:00

Thank you, Robert!

So, if I want to put $H to a %Date property I do:

set s.Date=$H

do s.%Save()

for %TimeStamp property to set current date/time, I do what?

score 0 · Answer 3 · 2018-04-14T08:24:42-04:00

Evgeny Shvarov · Apr 14, 2018

Thanks, Vitaly! That's interesting!

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score 0 · Answer 4 · 2018-04-14T08:32:02-04:00

Robert Cemper · Apr 14, 2018

in technology space it's nice and compatible to the UNIX/LINUX world
in the commercial arena it is just an alien

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score 0 · Answer 5 · 2018-04-16T03:07:18-04:00

This datatype is not present in (currently latest) Caché 2017.2; it appears to be IRIS-only. That rather limits its usefullness. Besides, what is the performance of a datatype, and where is that a bottleneck?

score 0 · Answer 6 · 2021-10-12T17:24:00-04:00

Hi Robert,

Why did you say that the %TimeStamp datatype is the equivalent of the full $h? It's true that %Date/%Time do the conversion from internal date/time values to/from external. But %TimeStamp, %DateTime, and %StringTimeStamp do not do any internal/external conversion. It's just for the YYYY-MM-DD HH:MM:SS external timestamp. Is there something I'm missing?

%PosixTimeStamp does convert, but it's not $h internally.

score 1 · Answer 7 · 2018-04-14T08:30:19-04:00

Robert Cemper · Apr 14, 2018

set s.TimeStamp=$zdt($H,3)

it is already in ODBC format.

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score 0 · Answer 8 · 2018-04-14T10:28:55-04:00

$zdt($H,3)

When working with $zd* functions It's better to specify what you need explicitly, because otherwise locale change can be an unwelcome surprise:

$zdt($H,3,1,0)

score 0 · Answer 9 · 2018-04-14T14:45:35-04:00

Robert Cemper · Apr 14, 2018

that's default anyhow

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score 0 · Answer 10 · 2018-04-14T14:59:00-04:00

Other locales could have TimeFormat property not equal to 1, there are also custom locales.

I completely agree that in a wide range of scenarios defaults work fine, or rather defaults are what we expect them to be. However, that is not always the case, so I prefer (and advice) to use macros for $zd* functions with all relevant parameters specified.

score 1 · Answer 11 · 2018-04-16T03:37:00-04:00

Time in Posix is the time as %Integer counting from Jan 1st, 1970. A UNIX definition.
dates before are negative integers (e.g. birthdate before 1970 )
[that was a reason to start $h with Jan 1st, 1840. The year the oldest veteran (in 1960) from civil war at MGH was born ]