"Michael Gentry (Yes, I'm a Contractor)" <michael_gentr..anniemae.com>
wrote:
> It is an insert, followed by a DELETE, in the same DataContext. Here is
the
> relevant stack dump (Cayenne 1.1):
If it's 1.1, that's before my changes with delete and optimistic locking.
>
org.objectstyle.cayenne.access.ContextCommit.appendOptimisticLockingAttribut
> es(ContextCommit.java:564)
>
org.objectstyle.cayenne.access.ContextCommit.prepareUpdateQueries(ContextCom
> mit.java:426)
The line above says it's happening for an update query. Can you figure out
what's in that update query -- it might shed more light.
Perhaps you have a leftover update operation sitting around in a context
that either didn't get committed or didn't get rolled back after a problem.
One of the problems I recently hit was that these non-WebObject servlets
happily process multiple requests by the same session at the same time (no
forced serialization). Thus, I had a user submit a request that created a
user account, then got impatient (because it was delaying on sending an
email with an activation code), and hit submit again. I was using
BasicServletConfiguration to get the DataContext bound to the session, and
that second request started running while the first action was still in
progress using the same DataContext (because it was the same session). A
second copy of the user account was added to the datacontext, then it
committed both copies, leaving an empty context when the first session
finally got around to committing it.
Since then, I've forced serialization of all requests by the same session.
I also now explicitly check if my DataContext is dirty as my code should
never leave a DataContext in a dirty state between requests.
if (dataContext.hasChanges())
{
String dirtyDataContextString = "Dirty DataContext found: \n";
Iterator it = dataContext.deletedObjects().iterator();
if (it.hasNext()) dirtyDataContextString += " Deleted
Objects:\n";
while (it.hasNext()) {
DataObject object = (DataObject) it.next();
dirtyDataContextString += " " + object + "\n";
}
it = dataContext.modifiedObjects().iterator();
if (it.hasNext()) dirtyDataContextString += " Modified
Objects:\n";
while (it.hasNext()) {
DataObject object = (DataObject) it.next();
dirtyDataContextString += " " + object + "\n";
}
it = dataContext.newObjects().iterator();
if (it.hasNext()) dirtyDataContextString += " New Objects:\n";
while (it.hasNext()) {
DataObject object = (DataObject) it.next();
dirtyDataContextString += " " + object + "\n";
}
NotificationManager.getInstance().reportProgrammingError(identityString, new
RuntimeException(dirtyDataContextString));
// can't dump changes because another thread might be using it
// dataContext.rollbackChanges();
// create a temporary new DataContext and hope the problem goes
away next time.
dataContext = DataContext.createDataContext();
}
>
org.objectstyle.cayenne.access.ContextCommit.commit(ContextCommit.java:156)
>
org.objectstyle.cayenne.access.DataContext.commitChanges(DataContext.java:12
> 66)
>
org.objectstyle.cayenne.access.DataContext.commitChanges(DataContext.java:12
> 36)
> qm.QueueDetails.processFormSubmission(QueueDetails.java:386)
> ...
> (everything else is Tapestry cruft)
>
>
> dataObject.getObjectId() returns:
>
> (org.objectstyle.cayenne.ObjectId) FENotification: <identifier: [..0ab17>
>
> But
>
dataObject.getDataContext().getObjectStore().getRetainedSnapshot(dataObject.
> getObjectId()) returns:
>
> null
>
>
> So, insert object, then delete it (in same DC) and then boom. Null
pointer
> exception. The DC is stored in a Tapestry Visit. The delete is done in a
> different page, but immediately after the insert. And it doesn't happen
> every time. :-)
>
> /dev/mrg
>
>
>
> > -----Original Message-----
> > From: Mike Kienenberger [mailto:mkienen..laska.net]
> > Sent: Tuesday, March 01, 2005 6:29 PM
> > To: cayenne-use..bjectstyle.org
> > Cc: Gentry, Michael (Contractor)
> > Subject: appendOptimisticLockingAttributes map snapshot error
> > duringinsert/update optimistic locking delete [Was: Re: Does this look
> > familiar?]
> >
> >
> > "Michael Gentry (Yes, I'm a Contractor)" <michael_gentr..anniemae.com>
> > wrote:
> >> /**
> >> * Appends values used for optimistic locking to a given snapshot.
> >> */
> >> private void appendOptimisticLockingAttributes(
> >> Map qualifierSnapshot,
> >> DataObject dataObject,
> >> List qualifierAttributes) throws CayenneException {
> >>
> >> Map snapshot =
> >> dataObject.getDataContext().getObjectStore().getRetainedSnapshot(
> >> dataObject.getObjectId());
> >>
> >> Iterator it = qualifierAttributes.iterator();
> >> while (it.hasNext()) {
> >> DbAttribute attribute = (DbAttribute) it.next();
> >> String name = attribute.getName();
> >> if (!qualifierSnapshot.containsKey(name)) {
> >> qualifierSnapshot.put(name, snapshot.get(name));
> >> }
> >> }
> >> }
> >>
> >>
> >> For some reason, I thought you had added the optimistic locking stuff
> > to
> >> Cayenne.
> >
> > Yeah, I provided the original patches, although Andrus did a lot of
> > cleanup
> > and refactoring work before committing them.
> >
> >
> >> Every now and then I get an exception on the "Map snapshot = ..."
> >> line. It *usually* happens when I do an insert and then go do an
> > update.
> > I
> >> haven't quite nailed down exactly what is going on, but thought if you
> > had
> >> written that part, you could give me a brief overview of what it's
> > trying
> > to
> >> do and then I could try to debug better.
> >
> > I didn't do this particular part, but Andrus and I just talked about it
> > as I
> > hit an issue with it when adding optimistic locking on deletes.
> >
> > What this is supposed to do is collect the old values of each object to
> > optimistically-update and bind them to the batch update query.
> > I *think* but am not completely sure that getRetainedSnapshot() is a
> > cache
> > of these values explicitly saved for this purpose and is different from
> > getCachedSnaphot (which is performance-related and isn't guranteed to
> > exist).
> >
> > The actual exception generated would be helpful.
> >
> > If I had to debug a situation like this, I'd put in some code to output
> > a
> > stack trace every time the retained snapshot for your object changes.
> >
> > Andrus may have better ideas or more accuration information on this. He
> > was
> > about to get assigned the issue of retaining snapshot info for
> > optimistic
> > deletes anyway :) I just hadn't finished creating a test case yet.
> >
> > -Mike
>
This archive was generated by hypermail 2.0.0 : Wed Mar 02 2005 - 16:22:42 EST