Problem controlling the order of deletes

Question

Hello,
I built a very simple example that uses two Java classes (Department and Employee) with a one-to-many relationship. The property "name" of class Employee maps to the primary key column of the EMPLOYEE table in the database. Now if I remove all employees from a department and then insert one employee who happens to have the same name as one of ex-employees, the things go wrong:
[TopLink Info]: DatabaseSession(101)--acquire unit of work: 216
[TopLink Info]: DatabaseSession(101)--Connection(102)--SELECT NAME FROM MACIEJ.DEPARTMENT WHERE (NAME = 'IT')
[TopLink Info]: UnitOfWork(216)--begin unit of work commit
[TopLink Info]: DatabaseSession(101)--Connection(102)--begin transaction
[TopLink Info]: UnitOfWork(216)--Connection(102)--INSERT INTO MACIEJ.EMPLOYEE (NAME, FIRST_NAME, DEPARTMENT_NAME) VALUES ('Schinzel', 'Dieter', 'IT')
[TopLink Info]: UnitOfWork(216)--Connection(102)--DELETE FROM MACIEJ.EMPLOYEE WHERE (NAME = 'Marczukajtis')
[TopLink Info]: UnitOfWork(216)--Connection(102)--DELETE FROM MACIEJ.EMPLOYEE WHERE (NAME = 'Schinzel')
[TopLink Info]: DatabaseSession(101)--Connection(102)--commit transaction
[TopLink Info]: UnitOfWork(216)--end unit of work commit
[TopLink Info]: UnitOfWork(216)--release unit of work
This happens also when I am using the method setShouldPerformDeletesFirst(true). The deletes are still executed after the insert. The code follows.
ExpressionBuilder builder = new ExpressionBuilder(Department.class);
Expression constraint = builder.get("name").equal("IT");
UnitOfWork uow = this.session.acquireUnitOfWork();
uow.setShouldPerformDeletesFirst(true);
Department dep = (Department) uow.readAllObjects(Department.class, constraint).get(0);
uow.logMessages();
dep.removeAllEmployees();
// Employee emp = new Employee();
Employee emp = (Employee) uow.registerObject(new Employee());
emp.setName("Schinzel");
emp.setFirstName("Dieter");
dep.addEmployee(emp);
uow.commit();
Another problem I encountered is that I have to use registerObject() on the new Employee (still if the value of "name" is identical to one of the employee's names that I am removing), because otherwise I am getting this:
Local Exception Stack:
Exception [TOPLINK-6004] (OracleAS TopLink - 10g (9.0.4) (Build 031126)): oracle.toplink.exceptions.QueryException
Exception Description: The object [cern.toplink.try1.Employee@ec[ name: Schinzel ; 1st name: Dieter ; dep: IT ]], of class [class cern.toplink.try1.Employee], with identity hashcode (System.identityHashCode()) [236],
is not from this UnitOfWork object space, but the parent session's. The object was never registered in this UnitOfWork,
but read from the parent session and related to an object registered in the UnitOfWork. Ensure that you are correctly
registering your objects. If you are still having problems, you can use the UnitOfWork.validateObjectSpace() method to
help debug where the error occurred. For more information, see the manual or FAQ.
I would appreciate any hints how I can force the deletes to happen before the insert.
Cheers,
Maciej

Answer 1

You cannot have two different objects in the same unit of work with different primary keys.
You must either update the object instead of deleting and inserting it, or split the operation across two units of work.
The setShouldPerformDeletesFirst only applies to publicly deleted objects, not objects that are deleted through private owned relationships. If you did not mark the relationship as private-owned and deleted the objects through uow.deleteObject then the deletes would be processed first. However you should still try to avoid having two different objects with the same primary key in the same unit of work.