Direct to field mapping to a foreign column

Question

I am using toplink workbench to map an attribute to a column in a foriegn table.
Example:
Table Emp {
EmpID,
AddressID, -- (Foriegn Key to the table Address)
StreetName }
Table Address {
AddressID, (Primary Key)
StreetName }
Class Emp{
empId;
addressId;
streetName;
Class Address {
addressId;
streetName;
In the workbench I have the descriptors defined and I am trying to map attribute 'Emp->streetName' to the column 'Address->StreetName'.
I added the the Address table in the advanced properties->Multitable Info of Emp class and also defined the association between the tables.
I mapped the 'streetName' property to the the 'Address->StreetName' using a direct to field mapping.
When I do getter on the streetName of the Emp class I get Null and I don't see any query getting executed in the Toplink to retrieve the streetName.
I don't want to load the complete Address object just to grab the streetName from the Address table.
Did anybody try to do something similar? if yes I would appreciate your hint.
-Rama

Answer 1

TopLink for POJOs does not support lazy loading of primitive type attributes. Lazy loading is only possible with relationships (i.e., one-to-one, one-to-many, many-to-many).
Mapping the same column data to two different classes does entail a number of complications but regardless, you'll eventually have to perform a join between the EMP and ADDRESS table to obtain the street name associated with an Employee. If you model your Employee-Address relationship as a one-to-one rmapping with Employee having an attribute of type Address:
class Emp {
    long id;
    Address address;
class Address {
   long id;
   String streetName;
}you can configure the relationship to use joining[1] so that when you read an Emp you'll also read the associated Address in a single statement.
--Shaun
[1] http://www.oracle.com/technology/products/ias/toplink/doc/10131/main/_html/oomapcfg002.htm#sthref3924