[hibernate-dev] 6.0 - HQL literals
Christian Beikov
christian.beikov at gmail.com
Wed Jan 8 07:08:00 EST 2020
If a user enters a HQL literal, that user wants the literal to be
rendered like that if possible(which should always be possible).
The only thing we have to define is whether the literal is by default in
the JVM TZ, JDBC TZ or UTC. We could offer syntax variants that default
to UTC etc.
Not sure what makes sense, even if I like UTC more, to me it feels like
the default should be using the JDBC TZ(which by default is the JVM TZ)
and offer a dedicated literal syntax for the UTC variant as well as
support for specifying the TZ explicitly.
Am 08.01.2020 um 12:56 schrieb 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 <mailto:yoann at hibernate.org>
>
>
> On Wed, 8 Jan 2020 at 12:41, Christian Beikov
> <christian.beikov at gmail.com <mailto: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 <mailto: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 <mailto:yoann at hibernate.org>
> >
> >
> > On Tue, 7 Jan 2020 at 19:50, Steve Ebersole <steve at hibernate.org
> <mailto: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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