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Ios swift – SwiftData Error with Relationships between three models

I am trying to get SwiftData to work with 3 models that are all interconnected. The simplified models and an example View that throws the error are attached below.
Creating a Company and an aircraft works fine, however, when trying to create a flight, the runtime error

Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘Illegal attempt to establish a relationship ‘aircrafts’ between objects in different contexts

is thrown. Does anyone know what I might do wrong?

This is the small example to show the problem:

The View with Buttons to trigger the creation of new instances, while the model context is injected in the app struct with .modelContainer(for: [Aircraft.self, Company.self, Flight.self]):

struct ContentView: View {
    @Query var flights: [Flight]
    @Query var aircrafts: [Aircraft]
    @Query var companies: [Company]
    
    @Environment(.modelContext) private var modelContext
    var body: some View {
        VStack {
            Text("(companies.count) Companies")
            Text("(aircrafts.count) Aircrafts")
            Text("(flights.count) Flights")
            
            Button("Create Company") {
                let company = Company(name: "MyAirline", aircrafts: [], flights: [])
                modelContext.insert(company)
            }
            Button("Create Aircraft") {
                guard let company = companies.first else { return }
                let aircraft = Aircraft(company: company, flights: [])
                modelContext.insert(aircraft)
            }
            Button("Create Flight") {
                guard let company = companies.first,
                      let aircraft = aircrafts.first
                else { return }
                let flight = Flight(company: company, aircrafts: [aircraft])
                modelContext.insert(flight)
            }
            Button("Delete everything") {
                try? modelContext.delete(model: Flight.self)
                try? modelContext.delete(model: Aircraft.self)
                try? modelContext.delete(model: Company.self)
            }
        }
        .padding()
    }
}

Here are the three models with their relationships:

@Model
final class Company {
    @Attribute(.unique) let name: String
    
    @Relationship(deleteRule: .cascade, inverse: Aircraft.company)
    var aircrafts: [Aircraft]
    
    @Relationship(deleteRule: .cascade, inverse: Flight.company)
    var flights: [Flight]
    
    init(name: String, aircrafts: [Aircraft], flights: [Flight]) {
        self.name = name
        self.aircrafts = aircrafts
        self.flights = flights
    }
}

@Model
final class Aircraft {
    var company: Company
    
    @Relationship(deleteRule: .nullify, inverse: Flight.aircrafts)
    var flights: [Flight]
    
    init(company: Company, flights: [Flight]) {
        self.company = company
        self.flights = flights
    }
}

@Model
final class Flight {
    let company: Company
    let aircrafts: [Aircraft]
    
    init(company: Company, aircrafts: [Aircraft]) {
        self.company = company
        self.aircrafts = aircrafts
    }
}
Tags:

2

Answers


  1. 0

    You can’t set Relationship vars directly inside init function. Assign a value to them from outside

      let flight = Flight(company: company)
  flight.aircrafts = [aircraft]
  modelContext.insert(flight)

    Also convert aircraft from "let" constant to var :

      @Model
  final class Flight {
  let company: Company
  var aircrafts: [Aircraft]

  init(company: Company) {
    self.company = company
    self.aircrafts = []
  }
}

    PS: Change other models like this.

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  2. 0

    I believe your many-to-many relationship between Aircraft and Flight is the problem. It is an odd setup, at least, to my eye. Certainly a plane can be scheduled for many different flights, but I would expect a flight to use exactly one airplane. The crash is because you have explicitly defined relationships that can’t be achieved.

    I modified Flight to make it 1-many with Aircraft and was able to create flights:

    @Model
final class Flight {
    let company: Company
    let aircraft: Aircraft
    
    init(company: Company, aircraft: Aircraft) {
        self.company = company
        self.aircraft = aircraft
    }
}

    But it’s still not possible to delete a flight or aircraft.

    When I tested the code, the "Delete everything" button failed with this console message:

    error: Unhandled opt lock error from executeBatchDeleteRequest Constraint trigger violation: Batch delete failed due to mandatory OTO nullify inverse on Aircraft/company and userInfo {
NSExceptionOmitCallstacks = 1;
NSLocalizedFailureReason = "Constraint trigger violation: Batch delete failed due to mandatory OTO nullify inverse on Aircraft/company";
"_NSCoreDataOptimisticLockingFailureConflictsKey" =     (
);
}
CoreData: error: Unhandled opt lock error from executeBatchDeleteRequest Constraint trigger violation: Batch delete failed due to mandatory OTO nullify inverse on Aircraft/company and userInfo {
NSExceptionOmitCallstacks = 1;
NSLocalizedFailureReason = "Constraint trigger violation: Batch delete failed due to mandatory OTO nullify inverse on Aircraft/company";
"_NSCoreDataOptimisticLockingFailureConflictsKey" =     (
);
}

    I removed the explicit @Relationship macros and allowed SwiftData to infer the relationships instead. That worked smoothly, except that you can now be left with zombie flights and aircraft when deleting a Company. So there’s still some work to be done here with figuring out your relationships and delete rules.

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