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From Erik Bengtson <e...@jpox.org>
Subject Re: Feature proposal for JDO 2.1 maintenance: current DB time
Date Thu, 19 Oct 2006 18:26:25 GMT
Your 1st requirement is to retrieve the date on the client. A 2nd requirement
would be comparisons over database server date.

I have one sample for the 2nd requirement

Query query = newQuery("select from Person where startDate > new Date()");


Quoting Jörg von Frantzius <joerg.von.frantzius@artnology.com>:

> Hi Craig,
>
> I'm not so sure whether this is really what you want to see, but here's
> something:
>
>     Query query = newQuery("new Date()");
>     query.setResultClass(java.sql.Timestamp.class);
>     query.setUnique(true);
>     Date result = (Date)timeQuery.execute();
>
>
> That result Date can then be used to e.g. set an updated object's
> lastModification timestamp before committing it.
>
> Regards,
> Jörg
>
> Craig L Russell schrieb:
> > Hi Jörg,
> >
> > Sorry to exercise you more on this, but I'm still having a bit of
> > difficulty seeing how to use this feature.
> >
> > Could you please give us an example of the use case you describe
> > below? I'd like to see the JDOQL query that uses new Date() in action.
> >
> > Thanks!
> >
> > Craig
> >
> > On Oct 19, 2006, at 1:33 AM, Jörg von Frantzius wrote:
> >
> >> Hello Craig,
> >>
> >> as far as I can see that does satisfy our requirements. Once we are
> >> able to query for that date in JDOQL, we can use it e.g. for
> >> lastmodification timestamps and the like.
> >>
> >> Regards,
> >> Jörg
> >>
> >> Craig L Russell schrieb:
> >>> It's easy enough to define "new Date()" as being evaluated on the
> >>> back end for queries that are executed on the back end. And being
> >>> evaluated in the vm for queries that have a bound candidateCollection.
> >>>
> >>> But does this satisfy the requirements? Once you have a Date in
> >>> JDOQL, what can you do with it?
> >>>
> >>> Craig
> >>>
> >>> On Oct 16, 2006, at 11:58 AM, Erik Bengtson wrote:
> >>>
> >>>> +1. maybe "new Date()" could be the expression where evaluation
> >>>> occurs on the
> >>>> database.
> >>>>
> >>>> Quoting Jörg von Frantzius <joerg.von.frantzius@artnology.com>:
> >>>>
> >>>>> Dear experts,
> >>>>>
> >>>>> there had been several occasions where in our applications we had
to
> >>>>> determine the database server's current time(-stamp). In one
> >>>>> application
> >>>>> we needed it to synchronize sent JMS messages with visibility of
> >>>>> commits
> >>>>> in the database, and in another we need it for our simple replication
> >>>>> algorithm.
> >>>>>
> >>>>> In distributed systems in general it is often crucial for
> >>>>> synchronization purposes to have a common source of time information
> >>>>> that is accessible from all processes.
> >>>>>
> >>>>> It would be great if JDO2 could offer a way of doing that
> >>>>> independently
> >>>>> of the database, e.g. as a JDOQL function.
> >>>>>
> >>>>>
> >>>>> Regards,
> >>>>> Jörg
> >>>>>
> >>>>
> >>>>
> >>>>
> >>>
> >>> Craig Russell
> >>> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
> >>> 408 276-5638 mailto:Craig.Russell@sun.com
> >>> P.S. A good JDO? O, Gasp!
> >>>
> >>
> >
> > Craig Russell
> > Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
> > 408 276-5638 mailto:Craig.Russell@sun.com
> > P.S. A good JDO? O, Gasp!
> >
>
>




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