7:29 a.m.
On Fri, 5 Oct 2018 at 12:47, Steve Ebersole <steve(a)hibernate.org> wrote:
Ah good, its time for this yearly discussion :D
Lol :)
but don't we have better options now with the new Date/Time API?
The old "Date" certainly was ambiguous in this regard, as one had a
single business type which could be occasionally used as a universal
timestamp, occasionally as a local political/human meaning; with Date
it was up to us to try hard to do the "right thing", and it was hard.
With the new types I would expect that we can guide people by not
allowing mixed mappings; so the epoch based Instant gets mapped to
whatever the specific database has to map epoch based timestamps,
while the political types would not.
I would simply expect that we would disallow conversions between the
two - at least unless there's a very explicit request to break sanity
rules - but I'd rather have it sane by default so to encourage people
to use the right Java types for their specific needs.
Thanks,
Sanne
The problem is as Vlad points out. We are kind of forced to do *something* wrt timezone
to often times counteract what the JDBC driver will do. As I have always contended, imo
that saving a date into the database with any kind of timzone (other than UTC) is simply
wrong. I personally would never do it - and I think we've seen enough of the down
sides to doing it. As Sanne points out, storing epoch-based dates (Instant, etc) is
always the best option
One cool option would be an AttributeConverter that handles the timezone transformation,
combined with telling Hibernate to always use UTC for the JDBC timezone
On Fri, Oct 5, 2018 at 4:44 AM Sanne Grinovero <sanne(a)hibernate.org> wrote:
>
> On Fri, 5 Oct 2018 at 10:28, Vlad Mihalcea <mihalcea.vlad(a)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(a)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(a)hibernate.org
> > >
> > >
> > > On Fri, 5 Oct 2018 at 09:38, Gunnar Morling <gunnar(a)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@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(a)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(a)lists.jboss.org
> > >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev
> > >> _______________________________________________
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> > >>
> > >
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