I am having troubles with an optimization issue.

Let's imagine that I have to map PERSON owning CARS
I have 2 tables : PERSON and CAR, CAR having a foreign key, the PERSON key.
Now, let's say that I only need the CAR licence plate number in the frame of a one-to-many relation between PERSON and CAR.
How can I map such a relation? Is there a way to map only one particular attribute of an entity?

If I map the Car class, then I will get useless information (other cars attributes) that uses resources...

u can use named query for that.
u can select select number_plate from car where car.person_id = :person_id.

As far as I'm concerned (and that ain't much) when you have a relation, all primary keys from one table go to the other as Foreign keys.

There's no way to avoid this.


If you want to only have the plate sent to the other table, you gotta make it the only primary key on the car table.

Ok, licence number was maybe not a good example!
No matters if I get all the primary keys.
I want only one property, let's say the car's gas type, ONLY when I am manipulating Persons.
Then what I don't want is for example the car brand, the car price ect... even if those are mapped in the Car Class :

PERSON
id
name
adress

CAR
licenceNumber
Person_id
brand
price
gasType

I will give a try to Named Query