grails: one field, multiple classes

Question

I would like to track a Motor with a Grails application. At several occasions, the location of the motor changes, but the location type also changes. How do I efficiently store the current location?

A first attempt would be:

class Motor {
    String motornumber
    Locationtype lt
}

class Locationtype {
    String type
}

class Machine {
    String machinenumber
}

class Repaircompany {
    String companyname
}

Depending on Locationtype lt which is ONE of {"Machine","Repair"}, a Motor object shall store the machine id or the repaircompany id at which the motor is located at. "Machine" means: The Motor is deployed on a machine, "Repair" means: the Motor is currently being repaired.

So I would like to have a field location as a field inside Motor, but of which type? I know, each time I access location, I would have to evaluate lt.

I was thinking about a field inside a trait. Would I be off-track with that or is that the way to go?

Answer 1

There are many possible solutions here, and none is necessarily better than another based on the limited information provided. Two possible solutions:

Simplest: Add a nullable Machine field and a nullable Repaircompany field to the Motor object. Then either could be populated (or technically both) and you can work as needed from those values.

Likely better: Create a Location base class (can be abstract) and extend Machine and Repaircompany from it. In Motor, create a field of type Location which could then be populated with either subclass.

For either solution, you probably don't need a Locationtype any more. You can determine that via which field is populated (for solution 1) or via subclass (for solution 2).