Hello,

I have used Hibernate 3.0 for some time now, however I still consider myself as a newby. Latly I found this problem, which I did solve, however I do not know if I did solve it in the correct way.

I have the following objects. Semesters has a one to many relationship with Assignments, and an Assignment has a one to many relation with Subject.

In english this comes to that in a Semester you have more then one assignment of differen subjects.

In the Semester object I use a List to hold the different Assignments. The Assignment class has the methods get/setSemester which returns/sets the semester, get/setSubject which returns/sets the Subject and get/setId which returns/sets the id of the assignment (auto generated). The Subject class has the get/setId, get/setName and get/setDescription methods.

Now each time I change the assignments, I change the whole list. That is I do something as follows:

mySemester.setAssignments(newListOfAssignments);

However those elements in the previous list of assignment still have a reference to mySemester. And thus when I do save mySemester, I find that in the database I just added the new records, and not deleted the old ones (in the Assignments Table).

What I did , and did work is the following:

[code]
// Create a reference to the list of old assignments
List<Assignment> old = semester.getAssignments();

// Setting the selected newsletter inside the resource object.
SemesterService semesterService =
ServiceFactory.getSemesterService();
semester.setAssignments(assignments);
semesterService.update(semester);

// Removing reference of the other newsletter subscriptions of this user.
AssignmentService assignmentService =
ServiceFactory.getAssignmentService();
assignmentService.remove(old);
[/code]

That is I create a reference to the old list of assignments, I then set the new list of assignments in semester and persist the object (this will just add the new rows in the Assignments table in the database). And then I remove the assignments by setting transent all the elements in the list (This will remove the assignments from the Assignments Table in the database). This works because when i come to delete the assignments, semester no longer has a reference to those assignments.

I am sure there must be a more simple way how to implement this, and any help would me more then welcome.

Thanks,
kcorp

No I have any ideas on how I can make my code more logical. For example, is it an acceptable aproach that the code, to remove any referene of Assignment from Semester is moved to the SemesterDAO? So that all I have to do is persist the Semester object.

Or this may be clasified as a one of situation (and thus accepted) since in my code I am replacing one list with another?

thanks,
kcorp

Hi,

You need a bidirectional parent child relationship. Investigate, if more help is needed, ask.