Description Lukas 2010-11-01 08:30:10 EDT

Build Identifier: eclipselink-2.1.0

The ClassCastException happens when executing a ReadAllQuery using a SessionBroker:

// (Some client code)
Session session = ...; //a ServerSession
ReadAllQuery raq : ...;
ScrollableCursor sc = (ScrollableCursor) session.executeQuery(raq);
while (sc.hasNext()) {
...

The query returns a ScrollableCursor on which hasNext() is called. That is when the ClassCastException happens in Cursor.buildAndRegisterObject 
where a ServerSession object is being cast into type UnitOfWorkImpl:

//Cursor:buildAndRegisterObject:
if (this.session.isUnitOfWork() && (!query.isReportQuery()) && query.shouldMaintainCache()
		&& objectQuery.shouldConformResultsInUnitOfWork() || objectQuery.getDescriptor().shouldAlwaysConformResultsInUnitOfWork()) {
		Object object = objectQuery.conformIndividualResult(
			objectQuery.buildObject(row), (UnitOfWorkImpl)this.session, this.translationRow, this.selectionCriteriaClone, this.initiallyConformingIndex);
						
						
The if condition evaluates to true because objectQuery.getDescriptor().shouldAlwaysConformResultsInUnitOfWork() returns so (the mapping class sets the flag to true). Even though session.isUnitOfWork() returned false 
(it is a ServerSession) the if-body is entered nonetheless and the session object castet into typ UnitOfWorkImpl:

java.lang.ClassCastException: org.eclipse.persistence.sessions.server.ServerSession incompatible with org.eclipse.persistence.internal.sessions.UnitOfWorkImpl
	at org.eclipse.persistence.queries.Cursor.buildAndRegisterObject(Cursor.java:301)
	at org.eclipse.persistence.queries.ScrollableCursor.retrieveNextObject(ScrollableCursor.java:566)
	at org.eclipse.persistence.queries.ScrollableCursor.loadNext(ScrollableCursor.java:397)
	at org.eclipse.persistence.queries.ScrollableCursor.hasNext(ScrollableCursor.java:263)
	
	
I suggest that in the if-condition of method Cursor.buildAndRegisterObject the shouldAlwaysConformResultsInUnitOfWork() should not be ORed with isUnitOfWork() 
but rather in AND relation.

Reproducible: Always

Steps to Reproduce:
1. the mapping class has so set the flag alwaysConformResultsInUnitOfWork on the RelationalDescriptor
2. the client code has to run a query which returns a result in the form of a ScrollableCursor.
3. the client code has to run the query using a SessionBroker type session
4. call hasNext on the ScrollableCursor instance.
5. the ClassCastException should then occur