SwiftData relations

Question

I'm I'm playing with the new swiftData I'm try to understand how the relations work my happy to have to model class:

Each Flight on my APP contained many crews, I wrote the relation like in the following code but keep getting the error " Fatal error: Inverse Relationship does not exist"

How should we write this relation:

@Model
class Flight {
 @Attribute(.unique) var flightID: UUID
 var typeOfFlight: String
 var flightDateUTC : Date
 var flightNumber: String?
 
 @Relationship(.cascade) var flightData: FlightData
 @Relationship(.cascade) var flightTime : FlightTime
 @Relationship(.noAction) var aircraft : Aircraft?
 @Relationship(inverse: \CrewModel.name)
 var crews : [CrewModel]? //<-------------------------------
 
 init(flightID: UUID, typeOfFlight: String, flightDateUTC: Date, flightNumber: String? = nil, flightData: FlightData, flightTime: FlightTime, aircraft: Aircraft? = nil, crews: [CrewModel]? = nil) {
 self.flightID = flightID
 self.typeOfFlight = typeOfFlight
 self.flightDateUTC = flightDateUTC
 self.flightNumber = flightNumber
 self.flightData = flightData
 self.flightTime = flightTime
 self.aircraft = aircraft
 self.crews = crews
 }
}
@Model
class CrewModel{
 
 @Attribute(.unique) var id: UUID = UUID()
 @Relationship(.noAction, inverse: \Flight.flightID)
 var name : String?
 var crewID: String?
 var company: String?
 var isMe: Int?
 var email: String?
 var phone: String?
 var score: Int?
 var isPIC: Int?
 var isSIC: Int?
 var dataImage: Data?
 var comment: String?
 
 init(id: UUID, name: String? = nil, crewID: String? = nil, company: String? = nil, isMe: Int? = nil, email: String? = nil, phone: String? = nil, score: Int? = nil, isPIC: Int? = nil, isSIC: Int? = nil, dataImage: Data? = nil, comment: String? = nil) {
 self.id = id
 self.name = name
 self.crewID = crewID
 self.company = company
 self.isMe = isMe
 self.email = email
 self.phone = phone
 self.score = score
 self.isPIC = isPIC
 self.isSIC = isSIC
 self.dataImage = dataImage
 self.comment = comment
 }
}

Answer 1

When using the inverse parameter you only need to define the relationship in one of the model types. The value for inverse must point to a property of the type of the model.

in Flight

@Relationship(inverse: \CrewModel.flight) var crews : [CrewModel]?

and in CrewModel

var flight: Flight?

Answer 2

Adding on to Joakim’s answer, you shouldn’t be dealing with an optional array. It makes sense if you think of the scenario where no crew is assigned to a specific Flight, the array is going to be empty, not missing.

You should change it to the following for this reason:

@Relationship(inverse: \CrewModel.flight) var crews = [CrewModel]()

Also I’m creating an empty array at the model’s initialization, because you’re more likely to run into issues if you’re trying to insert a new Flight that already has references to other CrewModels, over simply creating the Flight, inserting it into SwiftData, and then appending CrewModels to it.