[hibernate-dev] 6.0 - HQL literals

[Yoann Rodiere]

> 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
>
>