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Re: Date-Only NSTimestamps
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Re: Date-Only NSTimestamps


  • Subject: Re: Date-Only NSTimestamps
  • From: Simon McLean <email@hidden>
  • Date: Thu, 3 Jan 2008 07:58:26 +0000

It is a problem when the value is saved during DST and then queried when DST is not in effect (or vice versa).

Aaahh, yes, I remember now. That's the big pain in the butt!

the default time time zone to GMT. But then you get a whole new world of pain because you have to convert timestamps on the fly for presenting to your users!

That actually turns out to be fairly easy because you use a common datetime formatter on the session for all of the user's time rendering. This can be used bi-directionally for WOTextFields as well and then it is not too tricky at all to achieve this.

I don't see how this is any different from what WO does already. NSTimestamps are always in GMT and get formatted to / from the local timezone. If you set the local timezone to GMT, you avoid problems with new NSTimestamp, but you still have problems with dates parsed from user input if you don't want to interpret that as GMT values. What am I missing?

Good question :-) The new NSTimestamp() is the main problem solved - including the querying in/out of DST. But let me change the tack a little...


What if we store the user's literal input at GMT too (so if they put 14:00 we store it at 14:00 GMT) then for the majority of uses there is no need to change anything on the fly. We can just push and pull values from the DB and display exactly what we get to the user. Queries will never go wrong because there are no DST issues. We are effectively normalising the timezone.

It then becomes an issue if you want to calculate the difference in time between to points in different time zones (ie. user 1 enters a date/time in BST and user 2 enters a date/time in EST and you want to calculate the difference between the 2 literal date/time's). You could solve this by storing the timezone of each record separately (i guess just as a the string abbreviation) and having a cover method which converts the timestamp on the fly:

public NSTimestamp myTimeStamp; // assume it exists and is stored in GMT.
public String myTimeZone; // assume it exists and is set to the users timezone.


public NSTimestamp myTimeStampInMyTimeZone() {
	GregorianCalendar gc = new GregorianCalendar();
	gc.setTime(date);
	int day = gc.get(GregorianCalendar.DAY_OF_MONTH);
	int mth = gc.get(GregorianCalendar.MONTH) + 1;
	int year = gc.get(GregorianCalendar.YEAR);
	int hour = gc.get(GregorianCalendar.HOUR_OF_DAY);
	int min = gc.get(GregorianCalendar.MINUTE);
	int sec = gc.get(GregorianCalendar.SECOND);
	NSTimeZone tz = NSTimeZone.timeZoneWithName(myTimeZone, true);
	return new NSTimestamp(year, mth, day, hour, min, sec, tz);
}

What else could go wrong ?

Simon
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  • Follow-Ups:
    • Re: Date-Only NSTimestamps
      • From: "Mr. Pierre Frisch" <email@hidden>
    • Re: Date-Only NSTimestamps
      • From: "Jerry W. Walker" <email@hidden>
References: 
 >Date-Only NSTimestamps (From: David Avendasora <email@hidden>)
 >Re: Date-Only NSTimestamps (From: Chuck Hill <email@hidden>)
 >Re: Date-Only NSTimestamps (From: Simon McLean <email@hidden>)
 >Re: Date-Only NSTimestamps (From: Chuck Hill <email@hidden>)
 >Re: Date-Only NSTimestamps (From: Simon McLean <email@hidden>)
 >Re: Date-Only NSTimestamps (From: Andrew Lindesay <email@hidden>)
 >Re: Date-Only NSTimestamps (From: Chuck Hill <email@hidden>)

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