Question

I have an entity that has a reference to another one like these:

class School {
   private boolean used = false;
}

class Student {
   @ManyToOne
   private School school;
}

The attribute used indicates that the School entity is whether used, referenced or not. So when created, a School entity should have used false, but once a Student makes a reference to it, the used must be turned to true. Is there any automatically way to do this like triggers in database?

I try to use @PrePersist and @PostPersist on Student entity like this but it doesn’t work:

@PrePersist
public void prePersist(){
    school.setUsed(true);
}

Thanks,

Answer 1

My thought is that School should also have a reverse list of students. i.e.

class School {
   private List<Student> students;
}

So when the school is loaded, you can easily access the list of students. Then finding out if a school is being used becomes very simple. You will not longer need a boolean flag, just this:

public boolean hasStudents() {
    return students.size() > 0;
}