Seek good method for deleting many to many relationship

Question

My question is as follows:
The relationship of Employee and Project is many to many. I set privately owned for employee-project relationship at toplink builder.
Employee class has a vector of valueholder attribute of Project list.
I write a function to remove a project relationship from Employee when his is no longer responsible for it.
public void removeProjectFromEmployee(String employeeId, String projectId)
throws Exception
DataSource src = this.getSource();
Employee emp = getEmployeeById(employeeId);
if (emp == null) {
throw new Exception("employee with id " + employeeId + " does not exist.");
else {
Vector projectVector = emp.getProjects();
for (int i=0; i<projectVector.size(); i++){
Project p=(Project)projectVector.elementAt(i);
if ((p.getProjId()).equals(projectId)) {
projectVector.removeElementAt(i);
emp.setProjects(projectVector);
src.registerObject(emp);
src.commit();
In here, i select the object of the employee and then remove one particular project from the vector. It is working but seemed to be quite stupid. Moreover, i worry about its performance when there are thousands of projects owned by an employee.
I think it is a very common operation but i am not very familiar with TOPLink at this moment. Could anyone please advise the correct and better way to deal with this situation?
Thanks

Answer 1

Hello,
Try registering your employee in the UnitOfWork before you re-set the collection onto it. This should resolve your problem.
Note: When you set the collection on the unregistered Employee object, you were modifying a shared, read-only instance of the object, and hence were making transactional changes visible to other threads non-atomically. There are a lot of good reasons why this is a bad thing.
I hope this helps,
Christian