[hibernate-dev] 6.0 - HQL literals

[Yoann Rodiere]

> Can't we just render a literal in the DBMS proprietary way as literal
again
> but with respective TZ information to avoid TZ issues in the JDBC driver?

This may be an option. We would need to take into account the default JVM
timezone, or the "jdbc_timezone" setting, to set the correct offset.
However, I believe some JDBC drivers (MariaDB?) have options to convert
between the JVM timezone and the DB timezone, because apparently some DBs
assume the timezone of date/time values to be something else than UTC. Not
sure SQL literals would be interpreted correctly in such scenarios.


Yoann Rodière
Hibernate Team
yoann at hibernate.org


On Wed, 8 Jan 2020 at 12:41, Christian Beikov <christian.beikov at gmail.com>
wrote:

> Can't we just render a literal in the DBMS proprietary way as literal again
> but with respective TZ information to avoid TZ issues in the JDBC driver?
>
> If we use an instant literal we use the UTC TZ in a SQL literal or function
> to render that.
>
> Yoann Rodiere <yoann at hibernate.org> schrieb am Mi., 8. Jän. 2020, 11:22:
>
> > > This does nothing with Type.  The way the grammar is defined it
> literally
> > understands each piece of the temporal.  So given, e.g., {2020-01-01}, we
> > know that 2020 is the year, etc.  This is the benefit of defining it
> > syntactically.
> >
> > I trust you can build a temporal correctly from a string. I'm more
> > concerned about passing that information to the JDBC driver through a
> > parameter, or even directly to the database through an SQL literal. Last
> > time I checked you had to use java.sql types to pass temporal parameters
> to
> > JDBC drivers, so you will have to convert the java.time value to a
> > java.sql.Timestamp or similar eventually. And *that* is much more tricky
> > that I, at least, originally thought.
> >
> > Among other quirks:
> >
> >    - creating a Timestamp from a year/day/etc. assumes the given
> >    year/day/etc. are in the default JVM timezone.
> >    - the JDBC driver will sometimes extract the year/day/etc. and
> interpret
> >    them as being in the DB timezone, or will sometimes use a DateFormat
> > with a
> >    timezone to convert it to the correct timezone. It depends on the
> driver
> >    and even the version of the driver.
> >    - java.sql.Timestamp and java.time do not rely on the same calendar:
> >    Julian/Gregorian calendar for one, proleptic Gregorian calendar for
> the
> >    other.
> >    - java.sql.Timestamp and java.time do not assume the same offsets for
> >    various zone IDs around and before 1900, when time zones were not a
> >    formalized concept.
> >
> > I've spent days on conversion problems between java.time and java.sql in
> > ORM over the last few months.
> >
> > Which is why I think using LocalDateTimeType to convert between the
> > LocalDateTime literal and the Timestamp would be a good idea. If you want
> > to rewrite that code for literals, sure that can work, but exhaustive
> > testing will be needed.
> >
> > > As counter-intuitive as it sounds, a ZonedDateTime actually includes an
> > offset to differentiate the overlap case you mention.
> >
> > Yep. That's why it accepts parsing a ZoneDateTime with both a zone ID and
> > an offset. Try this:
> > https://gist.github.com/yrodiere/278996f865a9854e222aea58b5a7f26e
> >
> > Note that a bug affects parsing ZoneDateTimes with both offset and zone
> ID
> > on JDK8 (fixed in 9): https://bugs.openjdk.java.net/browse/JDK-8066982
> > We have a helper to work around that in Search:
> >
> >
> https://github.com/hibernate/hibernate-search/blob/334e4aad5c776151bcf5dbb6d27bf61fc8a93443/util/common/src/main/java/org/hibernate/search/util/common/impl/TimeHelper.java#L38
> >
> > > I think the confusion here is in terms of (1) recognizing a temporal
> > literal and "parsing it" and (2) applying it to SQL.  Different parts of
> > the puzzle.
> >
> > Yep.
> >
> > Yoann Rodière
> > Hibernate Team
> > yoann at hibernate.org
> >
> >
> > On Tue, 7 Jan 2020 at 19:50, Steve Ebersole <steve at hibernate.org> wrote:
> >
> > > As far as I know, even Java does not support that.  A true zone-id
> would
> > >> be something like (for me) "America/Chicago".  If I ask Java to parse
> > >> "2020-01-01 10:10:10 America/Chicago +02:00" it just says no.  For me,
> > CST
> > >> (standard) and CDT (daylight savings) are really synonyms for offset -
> > >> either UTC-05:00 or UTC-06:00 depending on day of the year.
> > >>
> > >
> > > It seems like the proper syntax for that would actually be "2020-01-01
> > > 10:10:10+02:00 America/Chicago", but in my
> > > testing DateTimeFormatter#parseBest did not handle that form either
> > >
> > >
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