How to link to user record who made changes in audit trail

[D Tim Cummings]

Hi all

I want to set up a simple audit trail which basically links who was the person 
to create a record to that record. I am using Cayenne 3.2M1 and Tapestry 5.3.7. 
I figure I need to set up a data channel filter to catch changes to that record 
and then save a link to the user who made the change. 

The problem is, if I save the user in the data channel filter object when 
someone logs in, then all created records link to the last logged in user. 

If I save the user in a ThreadLocal in the data channel filter object, I get a 
different user each time (often blank) because the data channel filter seem to 
run in its own thread which changes each time.

I have been watching the excellent and now freely available podcast by Andrus 
Adamchik presented to WebObjects developers "Advanced Apache Cayenne" where he 
talks about lifecycle events, (callbacks, listeners), caching, data channel 
filters, clustering, in cayenne 3.2M1.
https://itunes.apple.com/podcast/webobjects-podcasts/id270165303?mt=2#
In Andrus's sample code he uses AuditableProcessor, but I couldn't think how to 
use it to solve this problem.

Here is a copy of my listener/data channel filter with the ThreadLocal code.

Thanks 

Tim


public class AuditListener implements DataChannelFilter {
  
  private static final Logger logger = 
LoggerFactory.getLogger(AuditListener.class);
  
  private ThreadLocal<Integer> tlUserId;

  @PrePersist(entityAnnotations=TagCreateCancel.class)
  void doPrePersist(DataObject object) {
    if ( object instanceof AuditableCreateCancel ) {
      AuditableCreateCancel acc = (AuditableCreateCancel) object;
      TblPerson user = getTheUser(object.getObjectContext());
      acc.setTblPersonCreate(user);
    }
  }
  
  private TblPerson getTheUser(ObjectContext oc) {
    Thread t = Thread.currentThread();
    Integer idUser = tlUserId.get();
    if ( idUser == null ) {
      logger.info("Thread " + t.getId() + " idUser == null ");
      return null;
    }
    logger.info("Thread " + t.getId() + " Looking for TblPerson " + idUser);
    TblPerson p = Cayenne.objectForPK(oc, TblPerson.class, idUser.intValue());
    return p;
  }

  @Override
  public void init(DataChannel channel) {
    tlUserId = new ThreadLocal<Integer>();
  }

  @Override
  public QueryResponse onQuery(ObjectContext originatingContext, Query query, 
DataChannelFilterChain filterChain) {
    return filterChain.onQuery(originatingContext, query);
  }

  @Override
  public GraphDiff onSync(ObjectContext originatingContext, GraphDiff changes, 
int syncType, DataChannelFilterChain filterChain) {
    try {
      return filterChain.onSync(originatingContext, changes, syncType);
    } finally {
      //
    }
  }
  
  public void setTheUserId(int idUser) {
    Thread t = Thread.currentThread();
    logger.info("Thread " + t.getId() + " setTheUserId " + idUser);
    tlUserId.set(Integer.valueOf(idUser));
  }
  
}