I've just done something like this, along these lines:
private class ProcessImages extends Task<Void>
{
private int imageCount = 0;
private int listSize;
@Override
protected Void call() throws Exception
{
String sql = ....
SQLTemplate imgQry = new SQLTemplate( ImageMeta.class, sql );
imgQry.setCacheStrategy( QueryCacheStrategy.NO_CACHE );
imgQry.setFetchingDataRows( true );
List<DataRow> imgList = getNewContext().performQuery( imgQry );
listSize = imgList.size();
imgList.parallelStream().forEach( this::processImage );
return null;
}
private void processImage( DataRow imgID )
{
updateProgress( ++imageCount, listSize );
ImageBlob imgBlob = Cayenne.objectForPK( getNewContext(),
ImageBlob.class, imgID.get( "MED_IM_ID" ) );
// do stuff to imgBlob
imgBlob.getObjectContext().commitChanges();
}
}
regards
Jurgen
-----Original Message-----
From: Hugi Thordarson
Sent: Friday, June 19, 2015 12:32 AM
To: user@cayenne.apache.org
Subject: Re: Cayenne and threading
“Contexts are cheap”. Word’s I’m living by from now on, thanks!
- hugi
On 18. jún. 2015, at 22:29, John Huss <johnth...@gmail.com> wrote:
Contexts are cheap. You can create a new one on each iteration (or bind
one
to each thread ahead of time and reuse them) and localize the object and
save. Or do the write as plain sql.
On Thu, Jun 18, 2015 at 5:17 PM Hugi Thordarson <h...@karlmenn.is> wrote:
Thanks for the reply John, I suspected it couldn’t really be *this* good
:).
But if there are any takers, I’d love to hear how experienced folks would
approach multithreaded DB writes for tasks such as this using Cayenne.
To make things more clear; what’s happening in the lambda in my actual
project is that I’m performing OCR on an image linked to each Receipt
object and storing the resulting text. So, basically; a long running
task,
performing an operation on fetched objects and updating them.
When using EOF I’ve been bypassing DB writes entirely during the
multithreaded OCR stage by writing OCR results to disk. Once OCR is
complete for all receipts, I read the text files back form disk and
update
the DB.
Optimally, I’d like to be able to update the objects (and save to the DB)
as I’m iterating through the receipt objects. Any ideas?
Cheers,
- hugi
On 18. jún. 2015, at 21:48, John Huss <johnth...@gmail.com> wrote:
No, I don't think that's a good idea. The same context shouldn't be
shared
among threads. If you're doing pure SQL operations (like SQLTemplate)
and
not touching DataObjects you may be ok, but otherwise not.
But yes, Executors are great, especially with lambdas.
John
On Thu, Jun 18, 2015 at 4:31 PM Hugi Thordarson <h...@karlmenn.is>
wrote:
Hi all.
Coming from EOF I’ve been mentally trained to believe anything threaded
will bite you in the ass in a bad way. Using Cayenne, I’m now writing
threaded code and loving it, but I just wanted to double check with the
community; Is it really OK for me to do stuff like I’m doing in the
following code? It’s a somewhat extreme example since I'd never
actually
commit for each iteration, just looking for some good practices, advice
or
an “ARE YOU CRAZY?” comment :).
public void main( String[] argv ) {
ObjectContext oc = // get my ObjectContext
ExecutorService executorService = Executors.newFixedThreadPool(
Runtime.getRuntime().availableProcessors() );
List<Receipt> receipts = oc.select( new SelectQuery<>(
Receipt.class ) );
for( Receipt receipt : receipts ) {
executorService.execute( () -> {
receipt.setCreationDate( new Date() );
oc.commitChanges();
} );
}
executorService.shutdown();
}
Cheers,
- hugi
// Hugi Thordarson
// http://www.loftfar.is/ <http://www.loftfar.is/>
// s. 895-6688
