[hibernate-dev] Should the LocalTimeType use the globally configured TimeZone?

[Sanne Grinovero]

On Fri, 5 Oct 2018 at 10:28, Vlad Mihalcea <mihalcea.vlad at gmail.com> wrote:
>
> Hi
>
> IMO no timezone conversion whatsoever should be applied when
> > persisting LocalDateTime as it doesn't contain any TZ information.
>
>
> That's not very easy to do since either the JDBC Driver or the database
> engine might to the timezone conversion based on the underlying setting.
>
> In fact I'd even recommend to use a string-based column type to store
> > LDT, as it avoids these kinds of issues altogether.

+1 I think we need to enforce that. Mapping a Java type which is
explicitly designed to be insensitive to TZ should not be stored into
a type which is sensitive to it. That would otherwise defeat the
purpose of using these specific types.

If people really want to convert stuff, that's business logic. So that
belong in the business layer: let them do explicit conversion in their
own code before invoking the setter of an entity, that will also help
to bring awareness on any conversion issue they might have.

>
>
> Actually, a Long (BigInt) column type with the epoch would be more suitable
> than a CHAR-based column since it's more compact and achieves the same goal.
> However, many clients will not want to store Date/Time in Int or String
> columns as explained in the following article:

-1

let's use Epoch based numerics for Java types which are based on
Epoch. e.g. java.time.Instant.

People can always transform a date into an epoch-independent number by
simply encoding it as a number;
e.g. "2018-10-31" -> 20181031 . I guess it could save you some bytes
but I'd be skeptical on doing this automatically.

>
> https://www.periscopedata.com/blog/better-sql-schema
>
> Maybe introducing another value for "hibernate.jdbc.time_zone" ("as_is"?)
> > that would also impact how we map timezone-less types, would be a good idea?
>
>
> We would have to introduce a new configuration property as a strategy where
> the current behavior is "legacy"
> while the new one must be explicitly enabled.
>
> Vlad
>
> On Fri, Oct 5, 2018 at 11:17 AM Yoann Rodiere <yoann at hibernate.org> wrote:
>
> > > In fact I'd even recommend to use a string-based column type to store
> > > LDT, as it avoids these kinds of issues altogether.
> >
> > Or just, you know, "timestamp without timezone". Where possible.
> >
> > More to the point, I agree with Vlad's proposition, and I also think ORM
> > should avoid messing with timezones as much as possible: when the user
> > didn't provide one (LocalDate, LocalDateTime, Date), don't store one, when
> > he provided one (ZonedDateTime, OffsetDateTime, Calendar, ...), store it
> > exactly as provided. The goal being to return the exact value that was
> > persisted when later retrieving the data.
> > But unfortunately I think there is a lot of legacy behaviors that differ
> > from this, so any attempt at "fixing" it would break compatibility and make
> > someone angry.
> >
> > Maybe introducing another value for "hibernate.jdbc.time_zone" ("as_is"?)
> > that would also impact how we map timezone-less types, would be a good idea?
> >
> >
> > Yoann Rodière
> > Hibernate NoORM Team
> > yoann at hibernate.org
> >
> >
> > On Fri, 5 Oct 2018 at 09:38, Gunnar Morling <gunnar at hibernate.org> wrote:
> >
> >> IMO no timezone conversion whatsoever should be applied when
> >> persisting LocalDateTime as it doesn't contain any TZ information.
> >>
> >> If the target column type requires a TZ, it should be set to UTC,
> >> storing the given value without any shift. I.e. the LDT value
> >> 2007-12-03T10:15:30 should be stored as 2007-12-03T10:15:30 at UTC, no
> >> matter what's the VM's timezone or any TZ related config. This allows
> >> to retrieve the original value later on, also if e.g. the loading VM
> >> is in a different TZ.
> >>
> >> In fact I'd even recommend to use a string-based column type to store
> >> LDT, as it avoids these kinds of issues altogether.
> >>
> >> --Gunnar
> >>
> >>
> >>
> >>
> >>
> >> Am Fr., 5. Okt. 2018 um 07:15 Uhr schrieb Vlad Mihalcea
> >> <mihalcea.vlad at gmail.com>:
> >> >
> >> > Hi,
> >> > While reviewing this Jira issue:
> >> >
> >> > https://hibernate.atlassian.net/browse/HHH-12988
> >> >
> >> > and further discussing it via Twitter, I wonder if we should persist
> >> > LocalTime as-is without any TimeZone transformation
> >> > that may be done if we enable `hibernate.jdbc.time_zone`?
> >> >
> >> > According to the Date/Time API, LocalTime should not be relative to any
> >> > TimeZone.
> >> >
> >> > If we make this change, it means we need to use a LocalTime SQL
> >> descriptor
> >> > that ignores the jdbc.time_zone property,
> >> > and the change is going to break compatibility as well.
> >> >
> >> > Vlad
> >> > _______________________________________________
> >> > hibernate-dev mailing list
> >> > hibernate-dev at lists.jboss.org
> >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev
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> >>
> >
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