[hibernate-dev] HHH-11396 - Timezone handling

[Jordan Gigov]

The driver just has to use the available `getDate/getMonth/getYear`
functions of the java.sql.Date class, because they're what's intended
by the API. The problem is that the MySQL driver tries to do more than
that, when their database doesn't even support time zones.

On 14 March 2017 at 12:17, Christian Beikov <christian.beikov at gmail.com> wrote:
> So you are saying that it should be the JDBC drivers responsibility to
> add the JVMs local timezone offset to the java.sql.Date so the
> normalization can subtract the offset again? I would be ok with that,
> but is it really the responsibility of the JDBC driver?
>
>
> Mit freundlichen Grüßen,
> ------------------------------------------------------------------------
> *Christian Beikov*
> Am 14.03.2017 um 10:39 schrieb Jordan Gigov:
>> What java.sql.Date does is wrong for many reasons (mostly because it
>> extends java.util.Date which is a horrible API), but I think Vlad laid
>> it out pretty well why it's a JDBC driver configuration problem and
>> not a Hibernate problem. If you simply rely on the Java API to use
>> handle it's l own TZ conversion without telling it any zones (which
>> that JDBC URL tells it), the problem should go away. The driver does
>> try to read the server's time-zone, though, so maybe using
>> `useTimezone=false` in the JDBC URL is the right solution, but it
>> certainly shouldn't be to try and appease every driver's individual
>> quirks.
>>
>> Even MySQL's own API works under the assumption that LocalDate should
>> be converted using the JVM's default time-zone.
>> https://github.com/mysql/mysql-connector-j/blob/release/5.1/src/com/mysql/jdbc/JDBC42Helper.java#L50
>>
>> On 14 March 2017 at 09:38, Christian Beikov <christian.beikov at gmail.com> wrote:
>>> Hey everyone,
>>>
>>> I'd like to get your opinion on something. We had this issues regarding
>>> timezone handling which Vlad closed pretty quickly saying it isn't a
>>> Hibernate problem and I generally agree, but still would like to know
>>> what you think about it.
>>>
>>> So basically what we do in the LocalDateJavaDescriptor(and also in some
>>> other places) is to use the value returned by java.sql.Date in some way
>>> and pack that into the target type. In this case this happens behind the
>>> scenes when invoking java.sql.Date.toLocalDate() but internally it just
>>> calls LocalDate.of(getYear() + 1900, getMonth() + 1, getDate()).
>>>
>>> Now IMO the problem really is in java.sql.Date because it does a
>>> timezone conversion. The user who created the issue HHH-11396
>>> <https://hibernate.atlassian.net/browse/HHH-11396> pointed out he was
>>> using a DATE column type because he wanted to have a simple date i.e.
>>> year, month and date. When using java.sql.Date and the consumer is in a
>>> timezone after UTC i.e. UTC+1, the calculations of java.sql.Date will
>>> subtract that offset during /normalization/ and the millisecond value
>>> will change by that offset. This means that a date in the DBMS that is
>>> 2000-01-01 will become 1999-12-31 when the client is in UTC+1.
>>>
>>> One possible fix is to simply configure UTC for the consumer, then there
>>> will be no timezone shift.
>>>
>>> I think what java.sql.Date does is wrong because a date has no time
>>> part, so there shouldn't be any time shifts. We should workaround that
>>> by shifting the millisecond value back when constructing a LocalDate.
>>>
>>> What do you think should we do? Does anyone maybe know why java.sql.Date
>>> behaves that way?
>>>
>>>
>>> --
>>>
>>> Mit freundlichen Grüßen,
>>> ------------------------------------------------------------------------
>>> *Christian Beikov*
>>> _______________________________________________
>>> hibernate-dev mailing list
>>> hibernate-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>
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