Possible to run something in the background?

Question

This is my situation: I have a Student class and a Clazz class. A student can belong to only 1 clazz and a clazz can have many students. These 2 classes are mapped to 2 database tables. In the following code, I remove all the JPA annotations.
class Student {
    private Clazz clazz;
    public void setClazz(Clazz clazz) {
        this.clazz = clazz;
        clazz.getStudents().add(this);
class Clazz {
    private List<Student> students;
}So to add a new student to an existing class, I do something like:
Student student = new Student();
Clazz clazz = entityManager.find(Clazz.class, clazzId);
student.setClazz(clazz);
entityManager.persist(student);Because of the line clazz.getStudents().add(this); in the Student.setClazz method, the application has to go to the DB and load all the existing students for that clazz (which takes a long time).
The Student and Clazz codes are very difficult for me to change (somebody wrote them and they don't wanna change). So I have to think of some way to load the clazz and all its student when I have the clazzId information. The duration from when I have the clazzId info until the student is saved to the db is about 1min.
This is what I did:
- I created a stateful session bean with an EXTENDED entity manager which has a method to return a clazz when we feed it a clazzId. So the returned clazz is persisted.
- I created a stateless session bean which has a timer. When I have the clazzId, I start the timer, give the timer a ClazzHolder instance.
class ClazzHolder {
    private Long clazzId;
    private Clazz clazz;
    private boolean done;
}- The timer gets the clazzId from the ClazzHolder instance, feeds that clazzId to the stateful bean, receives a persisted Clazz instance back, saves that Clazz instance in the ClazzHolder instance and turns the flag "done" to true.
It seems to me that the ClazzHolder instance the stateless session bean has is not the ClazzHolder instance that I pass to it (but the content is the same). I think it's because the ClazzHolder instance I pass to the session bean is serialized first, and then de-serialized to build an object and give to a method in the session bean.
Summary: my idea of using timer to load something before hand doesn't work.
My question is: is there any way to load something from the database and keep it persisted before hand?

Answer 1

Hi Naimesh,
thx for explanation. I am not sure, if I understood everything in the right way.
Where do you write the code for building the selection-screen? (PARAMETERS, SELECT-OPTIONS etc.)
If you write these commands in a class method, you will get a syntax error ( because it's forbidden per definition of ABAP objects). So, am I right assuming that you put the coding just at the beginning of the ABAP report ? And after START-OF-SELECTION-event you start the processing... ?
Furthermore, I don't really understand why you create an separate class for ALV. I found your "SAP abap help"-blog, where you explained the concept of MVC ((By the way, well done!), but you didn't mention an "ALV class" there..
Mh.. another question - have you ever combined MVC with object services?
At the moment I'm working on a software project where I use object services. I created 2 persistent classes via SE24 and one local class in my ABAP Report.
I don't really see possibility to implement MVC in this project without change very much of coding and class structure...
In my opinion the M (data&business logic) are my existing global classes and my local class is kind of Controller class?!
Thx in advance,
Anne