Unidirectional OneToOne with foreign key on opposite side

fs5 · **Joined:** Wed May 21, 2008 11:52 am **Posts:** 5

Hi,

is there a way to accomplish this mapping:

* 2 classes: Person and Address
* Person references Address (to-one), but not the other way round
* 2 tables: PERSON and ADDRESS
* atypical foreign key PERSON_ID in table ADDRESS references PERSON.ID

Is this mapping possible without having to declare a property "person" in class "Address"?

Kind regards,
Frank

nagkumar · **Posted:** Wed May 21, 2008 1:44 pm

Based on my current experience and reading the example of Bid and Item in Java Persistance with Hibernate book.. this does not seem to be possible.

However, I am trying to abstract out this dependency in a way that id related to forignkey etc are inherited and could be used by more than one class with out have to repeat the code in every fp class..

Regards,
Nagendra

fs5 · **Joined:** Wed May 21, 2008 11:52 am **Posts:** 5

nagkumar wrote:

Based on my current experience and reading the example of Bid and Item in Java Persistance with Hibernate book.. this does not seem to be possible.

Thank you for confirming my suspicion.

In the depicted constellation the to-one relationship Person->Address is essentially not an many-to-one but a "degenerated" one-to-many relationship. I hoped there would have been some (undocumented) mapping.

Kind regards,
Frank

Btw: OpenJPA seems to supports this constellation, also undocumented but pure JPA:

Code:

@Entity
public class Person {
   @OneToOne
   @JoinColumn(name="Address.Person_id", referencedColumnName="id")
   private Address address;
...
}

mswindel · **Joined:** Wed Nov 16, 2005 6:09 pm **Posts:** 5

Would a @ManyToOne not achieve your goal? Especially given this is not a 'true' one-to-one relationship.

Code:

@Entity 
public class Person { 
   @ManyToOne 
   @JoinColumn(name="Address.Person_id", referencedColumnName="id") 
   private Address address; 
... 
}

Ultimately you get a reference to Address in Person without having to declare any relationship in Address. On the other hand, if this is truely a @OneToOne then why is having both ends of the relationship a problem? Or have I totally missed the point?