Hi,
I see one issue with using the syntax "new Date()":
it might conflict
with the constructor expression used in the result
expression, because
both use the keyword "new". A constructor expression
is only supported
in the query result expression; it is used to wrap
values into a result
class element and it is evaluated on the client. The
expression "new
Date()" should be supported in the result and the
filter, it does not
wrap any other values and it is evaluated on the
database back end.
How about using a different syntax for the current
database date, e.g.
JDOHelper.CURRENT_DATE() ?
The other interesting issue with the example from
Jörg is that it does
not define a candidate class. I think this was on
purpose, because the
query should not access any tables in the database,
but just return the
current date. Maybe we could use the JDOHelper as
the candidate class in
this case? This would be something similar to the
DUAL table in oracle.
Regards Michael
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
<[EMAIL PROTECTED]>:
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
<[EMAIL PROTECTED]>:
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:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!
Craig Russell
Architect, Sun Java Enterprise System
http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!
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