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package org.apache.cayenne.util;
import org.apache.cayenne.ObjectContext;
import org.apache.cayenne.ObjectId;
import org.apache.cayenne.PersistenceState;
import org.apache.cayenne.Persistent;
import org.apache.cayenne.graph.GraphManager;
import org.apache.cayenne.reflect.ClassDescriptor;
/**
* An operation that merges changes from a single object registered in some ObjectContext,
* to a peer object in an ObjectConext that is a child of that context.
*
* @since 3.1
*/
public class ShallowMergeOperation {
private final ObjectContext context;
public ShallowMergeOperation(ObjectContext context) {
this.context = context;
}
public <T extends Persistent> T merge(T peerInParentContext) {
if (peerInParentContext == null) {
throw new IllegalArgumentException("Null peerInParentContext");
}
// handling of HOLLOW peer state is here for completeness... Wonder if we ever
// have a case where it is applicable.
int peerState = peerInParentContext.getPersistenceState();
ObjectId id = peerInParentContext.getObjectId();
ClassDescriptor descriptor = context.getEntityResolver().getClassDescriptor(
id.getEntityName());
GraphManager graphManager = context.getGraphManager();
// have to synchronize almost the entire method to prevent multiple threads from
// messing up dataobjects per CAY-845.
synchronized (graphManager) {
T object = (T) graphManager.getNode(id);
// merge into an existing object
if (object == null) {
object = (T) descriptor.createObject();
object.setObjectContext(context);
object.setObjectId(id);
if (peerState == PersistenceState.HOLLOW) {
object.setPersistenceState(PersistenceState.HOLLOW);
}
else {
object.setPersistenceState(PersistenceState.COMMITTED);
}
graphManager.registerNode(id, object);
}
// TODO: Andrus, 1/24/2006 implement smart merge for modified objects...
if (peerState != PersistenceState.HOLLOW
&& object.getPersistenceState() != PersistenceState.MODIFIED
&& object.getPersistenceState() != PersistenceState.DELETED) {
descriptor.shallowMerge(peerInParentContext, object);
if (object.getPersistenceState() == PersistenceState.HOLLOW) {
object.setPersistenceState(PersistenceState.COMMITTED);
}
}
return object;
}
}
}