Hi Bernd,
Längerich wrote:
Hi,
I have some problems understanding (and using) the concept of the cache when
using multiple databases and determining the object modification level at the
store method.
Assume we have two databases A and B with one being the default and one being
the backup database. Both connections are configured using the cache:
<object-cache class="org.apache.ojb.broker.cache.ObjectCacheDefaultImpl">
<attribute attribute-name="timeout" attribute-value="-1"/>
</object-cache>
Given the following code sequence with empty databases, I have some problems:
AnObject someObject = new AnObject();
[...]
PersistenceBroker defaultBroker =
PersistenceBrokerFactory.defaultPersistenceBroker();
defaultbroker.store(someObject); // resulting in an INSERT to the default DB
[...]
defaultBroker.store(someObject); // resulting in an UPDATE to the default DB
PersistenceBroker backupBroker = PersistenceBrokerFactory.createPersistenceBroker(new
PBKey("backup"));
backupBroker.store(someObject); // resulting in an UPDATE to the backup DB,
which fails as there is no such row in the DB
As far as I understand the code from PersistanceBrokerImpl, it should query the
cache and/or the DB:
/*
if PK values are set, lookup cache or db to see whether object
needs insert or update
*/
if (!insert)
{
insert = objectCache.lookup(oid) == null
&& !serviceBrokerHelper().doesExist(cld, oid, obj);
}
store(obj, oid, cld, insert);
The insert should be false, as the PK fields are not null, and the objectCache
for the backupBroker should give null.
I traced with P6Spy, but I can't detect a SELECT to determine the existence of
the row, so I assume the objectCache.lookup(oid) returns true.
Any hints?
You are right, OJB find the object in the cache (because you operate
with the same objects on different DB's using a shared cache) and
indicate to update the object instead of insert.
Do you really need a shared cache on your "backup" broker? I would
recommend to use a "per broker cache" (for backup-broker)
http://db.apache.org/ojb/docu/guides/objectcache.html#ObjectCachePerBrokerImpl
Then OJB will not find the object in the cache of backup-broker and
perform a DB select.
regards,
Armin
Bernd
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