[eluser]OverZealous[/eluser]
Hi cube1893, welcome to CodeIgniter and DMZ!
How much information is unique between those models? What I'm thinking is that you might decide to merge the three different vehicle types into one vehicles table, and then have a column called type, which you can store, for example, 'c', 'b', 'm' to distinguish between types.
Then it would be simple to query, say, bikes like this:
Code:
$v = new Vehicle();
$v->where('type', 'b')->get();
If you wanted all users who have cars, you could try this:
Code:
$u = new User();
$u->where_related_vehicle('type', 'c')->get();
Another benefit of this is that you could get a merged query of multiple vehicle types at once.
However, if those three tables are very unique, meaning they don't share much information, this might be inefficient. In that case, you might want to simply include a column (car_id, bicycle_id, motorbike_id) for each vehicle type, and then each type will be represented by a unique class (Car, Bicycle, Motorbike), and have a unique relationship to User.
The draw back here is that you now have 2 NULL columns per user (although those usually don't take up much room), and you have to manually ensure that each User only has one vehicle, by clearing all three vehicle ids before you save a new vehicle.
Finally, a third option, which isn't much better than the last one, would be to have a unique relationship table for all three types (cars_users, bicycles_users, motorbikes_users). This usually makes your database messy, and is a little harder to manage than the in-table relationships. However, no NULL columns.
