hi all,

I need help in understanding how the collection mapping works with hibernate.

I have this sample mapping in my application.

Mapping for class Employee

private Set departments; //Note here i havent given initialized to any value..

public Set getDepartments() {
return departments;
}

public void setDepartments(Set departments) {
this.departments = departments;
}

In my Dao class when i use employee.getDepartments().size() , this returns 0 sometimes for new employee and sometimes i am getting NullPointerException with employee.getDepartments() for the new employee.

I dnt understand this behavior of hibernate, how i am able to get the departments Set sometimes & null at rare times.

your response is awaited..

thanks in advance.

should be this:
if u save new employee with department=null after save, still departement == null, but if u retrieve employee from db departement will be empty set.

or maybe you sometime set departments with empty set and sometimes not

Its like in the Employee class my declaration as earlier shown is not initialized. And when i save the Employee i wont bother about the department mapping also.

But when i query employee.getDepartments() i am able to get Collection with size = 0 but sometimes (say 1 out 6) times it gives null Collection.

what may b da reason?

propably 1 out 6 means that u are doing it little different than other cases, try to simulate it in test