I am converting (re-implementing) an app to use SwiftData. Xcode is asking for BackingData when I create an instance of one of the SwiftData classes but I am coming up empty for an explanation of what this is and how to implement it properly. Any pointers? Original code snippet:

func addRace() {
        let racenum = races.count + 1
        let newRace = Race()
        newRace.raceNum = racenum
        ...

Which worked before SwifData. New code prompted by Xcode:

func addRace() {
        let racenum = races.count + 1
        let newRace = Race(backingData: <#BackingData<Race>#>)
        newRace.raceNum = racenum
        ...

I have been able to work around this issue by initializing all the properties when creating the class instance. This did not work until I changed the enum property defaults from ".case" to "Type.case". Seems that is an XCode bug with enums and SwiftData.