Hi all.
I've only been working with relational databases up to now, and have
some problems with JDO.
I seem to have some trouble grasping the basic design patterns with
POJO/JDO here.
This is probably a very basic issue, but its hard when the mind is
setup to think from an entirely different perspective :-).
So, what I want to do here is to have child objects of the same type
referenced from different parents.
For example...
Say we have a class Person, class CarRegister, class Car.
A Car class with a Key.
class Car {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key key;
...other persistent objects...
}
In Person, I have a list of Car objects that the person owns.
class Person {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Long id;
@Persistent
private List<Car> ownedCars;
}
In CarRegister, I also have a list of all Car objects registered.
class CarRegister{
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Long id;
@Persistent
private List<Car> registeredCars;
}
Is this possible? The documentation seem to suggest that a key is made
up of the entity parent id and some other stuff, which should mean
that the above wouldn't work. (The key value includes the key of the
entity group parent (if any) and either the app-assigned string ID or
the system-generated numeric ID).
I could of course save a list of keys/ids to Car objects instead, but
that to me would kind of defeat the purpose of this kind of database.
So I want a List of Car objects in both Person and CarRegister, and
they must somehow share the same objects in the database. This must be
one of the basic use cases, but I have been unable to find an optimal
solution for it.
Thanks in advance.
BR, Andreas
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