How do I reducing the amount of joining when using one-to-one mappings?

Question

Examine the following example;
class Person
Address address;
String firstName, lastName;
class Address
Long addressId;
String state, city, zip;
Assume that both of these classes are mapped to tables in a database. Attributes such as Staff's name and Address's addressId, state, city, and zip are direct-to-field mappings. Staff's address attribute is a one-to-one mapping.
If you write the following expression:
Expression exp = new ExpressionBuilder(Person.class).get("address").get("addressId").equal(4L);
Toplink will create a query like the following:
select first_name, last_name, address_id, ...
from person t0, address t1
where t0.address_id = t1.address_id
and t1.address_id = 4;
This is an unneccesary join because the person table already has the column with the data in it since it has a foriegn key. Is there someway to tell toplink to not join the tables when the only thing you are querying on is if a foriegn key that already exists in the referenced table? What I would want/expect to see is the following:
select first_name, last_name, address_id, ...
from person t0
where t0.address_id = 4;
I beleive we are using TopLink version 10.1.3.1

Answer 1

In your initial query you're actually saying "find the Person who has an Address who's id is 4". Your second query is "find the Person who references an address who's id is 4". The first query requires there be an Address with ID 4, the other does not.
If you define a query key "addressId" for the ADDRESS_ID column on the Person descriptor you can write this query as:
Expression exp = new ExpressionBuilder(Person.class).get("addressId").equal(4L);This will result in the SQL you want.
--Shaun