JPA one-to-one relationship without column mapping - jpa

Question

I have a couple of entities with one-to-one relationships as such:
#Entity(name="stores")
public class Store implements Serializable {
#Id
#GeneratedValue(strategy= GenerationType.AUTO )
#Column(name="id")
private int id ;
// How should I set goal ?
private Goal goal ;
}
and:
#Entity(name="storeGoals")
public class Goal {
#Id
#GeneratedValue(strategy= GenerationType.AUTO )
#Column(name="goalId")
private int id ;
#OneToOne()
#JoinColumn(name = "storeId")
private Store store ;
}
My problem is how can I set the "goal" field in the Store entity?
Normally, I would do something like:
#Entity(name="stores")
public class Store implements Serializable {
...
#OneToOne()
#JoinColumn(name = "goalId")
private Goal goal ;
...
but in this case I can't, because the underlying "stores" table belongs to another application and can't be modified (by adding a "goalId" column).
What I need is for an instance of Store to be able to lookup its goal by finding a record in the storeGoals table that has the same storeId (Realizing of course that I could run into referential integrity issues...)
Any ideas on how to do that?
Thanks!

Answer 1

You might be looking for what is known as a bidirectional OneToOne relationship. This works the same as a bidirectional ManyToMany or OneToMany/ManyToOne relationship in that one side 'owns' the relationship and has control over setting the value in the foreign key; the other specifies it is 'mappedby' the other side, and so operates as if it is read-only. Both sides need to be kept in synch with any changes manually though; if you set one side but do not reflect the change in the other, JPA will not fix this for you.
In this case:
public class Store implements Serializable {
..
#OneToOne(mappedby="store")
private Goal goal ;
}