Javadoc
PUBLIC:
Define the target foreign key relationship in the 1-1 mapping.
This method is used for composite target foreign key relationships,
that is the target object's table has multiple foreign key fields to
the source object's primary key fields.
Both the target foreign key field and the source primary key field must
be specified.
The distinction between a foreign key and target foreign key is that the
1-1 mapping will not populate the target foreign key value when written
(because it is in the target table). Normally 1-1's are through foreign
keys but in bi-directional 1-1's the back reference will be a target
foreign key. In obscure composite legacy data models a 1-1 may consist of
a foreign key part and a target foreign key part, in this case both
method will be called with the correct parts.