Single reference into multiple objects - oop

Question

I am a bit lot about what to do in an OO/DB relation...
Here is the DB model :
CREATE TABLE User
Id
CREATE TABLE Location
userId
// EDIT oups, wrong !
// placeId
// Should be :
seatId
CREATE TABLE Game
locationId
Now some code :
class User
{
private Location locations[]; // need this for several reasons...
public function loadFromDatabase()
{
// Load data from DB
// ...
result = DB::query("SELECT Id FROM Locations WHERE userId="+this->Id);
foreach(result)
{
l = new Location();
l->loadFromDatabase(result);
locations[] = l;
}
}
}
class Location
{
private User user;
public function loadFromDatabase()
{
...
}
}
class Game
{
private Location location;
public loadFromDatabase()
{
/*
Here comes the problem :
how to have a reference to a location
created by the User class ?
*/
}
}
A User play Games in several Locations.
EDIT : And for each location the user plays on seat. Or on another seat...
When I want to know where a game has been played I access Game.location. And when I want to know who played it, I access Game.location.user
Here is my problem : I want the Game.location to be the same reference to one of the User.locations and I do not know how to do this...
And, globally, I feel something wrong about my code...
Any help ?
Thanks

Answer 1

Since you have a placeId in your Location table, I assume there is a Place table which describes what the places actually are, while the Location table simply represents the many-to-many mapping between users and places.
In that case, Location doesn't need to have an Id of its own and doesn't need to be a class, but Place does.
To load just one instance of each object from the database, cache the instances in a static map inside each class.
class Place
{
// Static
private static Place loadedPlaces[];
public static function get(id)
{
if (!loadedPlaces[id])
{
loadedPlaces[id] = new Place(id);
loadedPlaces[id]->loadFromDatabase();
}
return loadedPlaces[id];
}
// Non-static
private id;
public function loadFromDatabase()
{
// ...
}
}
Then to get references to places for the properties of a user or a game, you just access them via the static method.
class User
{
public function loadFromDatabase()
{
result = DB::query("SELECT placeId FROM Locations WHERE userId="+this->Id);
foreach(result)
{
places[] = Place::get(result);
}
}
}
class Game
{
public function loadFromDatabase()
{
place = Place::get(place);
}
}
This uses:
Lazy initialization, because places are only loaded when they are needed.
Multiton pattern, because there is only one instance of each place by id.
Not quite a factory method, because there's no object hierarchy involved.