Merging data from two data bases

Hi,

given is a master data base and a backup data base. All entries are stored to the master data base and  to the backup.
If anything fails (computer crashes) at startup I want to merge the data from the backup with the data of the master database.

The code I tried is like this:

      masterbroker = PersistenceBrokerFactory.defaultPersistenceBroker();
      ReportQueryByCriteria masterquery = QueryFactory.newReportQuery(Transaction.class,new Criteria());
      masterquery.setAttributes(new String[] {"id"});
      masterquery.setDistinct(true);
      Collection taids = masterbroker.getCollectionByQuery(masterquery);
      log.info("Master DB has "+taids.size()+" transactions");
      Criteria crit = new Criteria();
      crit.addNotIn("id",taids);
      backupbroker = PersistenceBrokerFactory.createPersistenceBroker(new PBKey(jcdalias));
      Query query = QueryFactory.newQuery(Transaction.class,crit);
      Collection tas = backupbroker.getCollectionByQuery(query);
      if (tas.size()>0) {
        log.warn("Backup DB has "+tas.size()+" transactions not stored in the master DB");
      }
      for (Iterator iter = tas.iterator(); iter.hasNext();) ...

The problem is when I reach the line

      Collection taids = masterbroker.getCollectionByQuery(masterquery);

I get a strange exception:

org.apache.ojb.broker.PersistenceBrokerException: Unexpected error while try to read 'ojbConcretClass' field from result set using column name CLASS_NAME main class was de.actosoft.accept.process.Transaction
	at org.apache.ojb.broker.accesslayer.RowReaderDefaultImpl.extractOjbConcreteClass(Unknown Source)
	at org.apache.ojb.broker.accesslayer.RowReaderDefaultImpl.readObjectArrayFrom(Unknown Source)
	at org.apache.ojb.broker.accesslayer.RsIterator.getObjectFromResultSet(Unknown Source)
	at org.apache.ojb.broker.accesslayer.RsIterator.next(Unknown Source)
	at org.apache.ojb.broker.accesslayer.ChainingIterator.next(Unknown Source)
	at org.apache.ojb.broker.core.QueryReferenceBroker.getCollectionByQuery(Unknown Source)
	at org.apache.ojb.broker.core.QueryReferenceBroker.getCollectionByQuery(Unknown Source)
	at org.apache.ojb.broker.core.QueryReferenceBroker.getCollectionByQuery(Unknown Source)
	at org.apache.ojb.broker.core.PersistenceBrokerImpl.getCollectionByQuery(Unknown Source)
	at org.apache.ojb.broker.core.DelegatingPersistenceBroker.getCollectionByQuery(Unknown Source)
	at org.apache.ojb.broker.core.DelegatingPersistenceBroker.getCollectionByQuery(Unknown Source)
[...]

The strange thing is the 'ojbConcretClass' where the repository_user.xml says:

<class-descriptor
    class="de.actosoft.accept.process.NullTransaction"
    table="ACC_TA"
>
    <field-descriptor
        name="ojbConcreteClass"
        column="CLASS_NAME"
        jdbc-type="VARCHAR"
        length="255"
    >
    </field-descriptor>
    <field-descriptor
        name="id"
        column="ACC_TAID"
        jdbc-type="INTEGER"
        primarykey="true"
        autoincrement="true"
    >
[...]

The SQL generated and executed looks fine (except that it contains redundant where clause parts):

1165921756841|-1||resultset|SELECT DISTINCT A0.ACC_TAID FROM ACC_TA A0 WHERE ( A0.CLASS_NAME IN (...)) AND  (A0.CLASS_NAME IN (...)|ACC_TAID = 1

If I remove the line 
      masterquery.setAttributes(new String[] {"id"});
everything works fine but I get all object instances instead of just a collection of ids.

Any hints? Is there any way to do what I want? I used db-ojb-1.0.4.jar and MS-SQL 2000.

Mit freundlichen Grüßen

i.A. Bernd Längerich
Softwareentwicklung

act'o-soft GmbH Payment Systems
World Wide Business Center
Habichtstrasse 41
22305 Hamburg

Phone: 00 49 40 61135432
Fax:     00 49 40 61135429
Mobile: -
eMail:   [email protected]
www.actosoft-payment-systems.de