Hibernate3.1:

I have Table A and Table B.

Fields in Table A
------------------
x - primary k
y - foreign key
z

fields in Table B
------------------
y - primary key
q
r

Tables A and B are joined by y and y.

In the mapping file I want to specify a one-ton-one where class B resides inside class A.

How do I specify how these tables are joined? The hibernate documentation says to use fomula when not mapping to the primary key of the owning entity however does not give an example of this case.


<class name="A" table="A" lazy="true">
<id name="id" column="x" type="long">
<generator class="foreign">
<param name="property">fieldProps</param>
</generator>
</id>
<property name="y" column="y" type="long"/>
<property name="z" column="z" type="long"/>

<one-to-one name="fieldProps" class="B" cascade="all"
formula="??????????????????????">
</one-to-one>
</class>

<class name="B" table="B" lazy="true">
<id name="id" column="y" type="long">
<generator class="increment" />
</id>
<property name="q" column="q" type="string"/>
<property name="r" column="r" type="string"/>
</class>

If you look at it from the other way around you get the simple case. You're simply mapping the inverse side of a bidirectional one-to-one mapping.
What kind of model are you trying to achieve here? Is it a parent-child relationship? In this case you could say that B is the parent and A is the child (A can't live when B ceases to exist because of the foreign key). It doesn't matter that B is 'contained' in A. This is just a navigation link, and in this case the reference to B in A would be the inverse one.

I think when they talk about mapping to the primary key they mean mapping two tables by both's primary keys, rather than primary to foreign.