Question

Two class:

Department Task

One department can have many tasks. One task can only belong to one department.

So use one-to-many or many-to-one?

---

one-to-many
class Department{
  private Set tasks;
}
class Task{
  ......
}
//
Department.hbm.xml
....
<set name="tasks">
    <key column="departId" />
    <one-to-many class="Task" />
</set>
.....

---

many-to-one

class Department{

}
class Task{
  Department depart;
}
//
Task.hbm.xml
....
<property name="depart">
    <many-to-one class="Department" />
</property>
.....

---

What’s the difference?

BTW,what is the difference between use the set and list?

And example using list(xml configuration)?

Answer 1

Your choices would depend on 2 things:

1. What are various scenarios under which this relationships are used. For e.g. if you need to list your tasks by departments than One to Many is what you would need. It would also be easy for you to load them once since you are using Hibernate.

2. If you update your tasks by department then you need the other relationship too.

However, remember this decisions have deep roots into your domain model and how you want to structure it. What are the usecases under which these entities are used. I would strongly recommend reading this SO thread and moreover watch this video by Eric Evans.

Hope that helps.