There is a many to many relationship between students and subjects. At the end
of the year this relationship has to be dissolved so new subjects can be
assigned to each student the next year.
I thought it was going to be easy. First, get all the students in a list with
a query. Then loop through this list while at the same time looping through
each student
| for(Student s : students){
| s.setYear(s.getYear() + 1);
| q = manager.createQuery("select ss from Student s join
s.subjects ss where s = :student");
| q.setParameter("student", s);
| List<Subject> subjects = q.getResultList();
| if(subjects != null && subjects.size() > 0){
| System.out.println("The number of subjects for student
" +
| s.getNames() + " " + s.getSurname() + " is " + subjects.size());
| Iterator<Subject> iter = subjects.iterator();
| while(iter.hasNext()){
| Subject sj = iter.next(); //This is where it hits
the fan
| subjects.remove(sj);
| }
| }
|
I've also tried using a set (Set subjects = s.getSubjects()) with the same
results. I also used a cast in the line with the problems.
This is a short version of the exceptions:
| javax.ejb.EJBException: null; CausedByException is:
| null
| at
org.jboss.ejb3.tx.Ejb3TxPolicy.handleExceptionInOurTx(Ejb3TxPolicy.java:46)
| at org.jboss.aspects.tx.TxPolicy.invokeInOurTx(TxPolicy.java:70)
| at
org.jboss.aspects.tx.TxInterceptor$Required.invoke(TxInterceptor.java:134)
| at
org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
|
There is also a
java.util.ConcurrentModificationException
| at
java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449)
| at java.util.AbstractList$Itr.next(AbstractList.java:420)
| at
au.com.databaseapplications.jtest.session.PrincipalSessionBean.newYear(PrincipalSessionBean.java:355)
|
The last line referred to in the exception above is the one indicated in the
code.
Any idea how one can do what seems to be simple?
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