Hi,
I have the following two classes: Student and Department.

class Student {
@Id
public void getId() {
...
}

...
@ManyToOne(optional = false)
@JoinColumn(name = "DEPT_ID")
public Department getDepartment() {
return this._department;
}

private Long _id;
private Department _department;
}

All this works fine. But the problem is that my foreign key, getDepartment has to return a Department object. I was wondering if this can be made to return a Long (which is the id of the department row concerned). The reason I was this is that I do not want to read in the entire department column (avoid a join of the user with the department table).

This problem becomes worse if the getDepartment is a set. Any set operation that requires equals/hashCode which I currently override to do business key based equality/ But any set operation leads to loading of all the department objects unnecessarily. I need to have this as a Set and not a bag.

Thanks,

You can simply map the department id as a property of type long and implement an additional method for retrieveing the department object if needed.

Thanks for the reply. Will this also work for @manytomany mappings with collections/sets?

No, I'm afraid not. You could model the many-to-many with an entity that connects the objects and use many-to-one associations instead: A n:1 AB 1:m B.

You can maybe write your own proxy implementation and use lazy-loading. But that is a complex way to go. I can't help you there, but you probably find enough information on the net.