Hi,

Got a question on one-to-one mapping. According to Tom Sedge's tutorial (http://www.xylax.net/hibernate/), the one-to-one mapping requires a shared PK between two persistent classes. However, that's not the usual way we implement in database (we usually set up a foreign key in one of the tables). I was wondering, is it (the shared PK) REQUIRED or is just one of the ways to implement one-to-one mapping?

I did see another example from "http://www.meagle.com:8080/hibernate.jsp" that does not use a shared key, but to include an object from the second class to the first class.

Thanks for your help.

Lilly

Did you try the reference documentation or Hibernate in Action?

Lilly,

Tom is not saying that you have to share the FK as in they both have the same foreign key value. He is saying that they will both have the same primary key. As in, both primary keys will have the same value.

Hibernate offers a couple of approaches for one-to-one mapping.

The 'reference documentation' is particular effective in explaining this. Admittedly, it's hard at first to know what you're reading.

Anyway -

Using a one-to-one mapping one of the things you can do is specify that one of the mappings use a 'foreign' id generator. This will tell hibernate that it must use the same primary key for this entity that it uses for the other mapped entity (this is quite clear I'm sure ;) )

ANOTHER approach, the one I prefer, is to use a many-to-one mapping which will result in the more familiar Relational approach you discussed. It will put a foreign-key on the table for which you are currently mapping to the table holding the other thing you're mapping.



Hopefully this provides a bit of help

Thanks to both of you. That helps a lot. You also help me to realize to read the reference documentation more thorough :)).

Lilly