Migrating a Transformable attribute from CoreData to SwiftData

Question

rlaurb OP

Created 2d

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I am migrating a CloudKit-synchronized multi-platform app from CoreData to SwiftData. (Xcode 27.0 beta 5).

One of my Models/Entities contains a Transformable attribute, which is defined in the CoreData model editor as:

and which is defined in the generated CoreData class as

@NSManaged nonisolated public var authorNames: [String]?

Using the built-in translation took, Xcode created a Model wich included

@Attribute(.transformable(by: "NSSecureUnarchiveFromDataTransformerName")) var authorNames: [String] = []

This compiles but does not run. In the function

func getModelContainer() throws -> ModelContainer {
    let storeURL = try FileManager.default.url(
            for: .applicationSupportDirectory, 
            in: .userDomainMask, 
            appropriateFor: nil, create: true)
        .appendingPathComponent(dbName)
    let modelConfiguration = ModelConfiguration(
            schema: dbSchema, url: storeURL,
            cloudKitDatabase: .automatic)
    let container = try ModelContainer(
            for: dbSchema,
            migrationPlan: MigrationPlan.self,
            configurations: [modelConfiguration])
    return container
}

the app throws a fatal error in the ModelContainer initializer,

SwiftData/SchemaCoreData.swift:398: Fatal error: Application must register a ValueTransformer for NSSecureUnarchiveFromDataTransformerName

So I added the following line of code at the top of this function:

    ValueTransformer.setValueTransformer(
            NSSecureUnarchiveFromDataTransformer(), 
            forName: .secureUnarchiveFromDataTransformerName)

which also compiles but also throws the same fatal error in the same place.

Can anyone suggest how to resolve this problem? This is a CloudKit synchronized app, so I am constrained in what I can do with this attribute.

Answer 1

rlaurb OP

1d

phspman, posting on a different thread, suggested replacing

@Attribute(.transformable(by: 
    "NSSecureUnarchiveFromDataTransformerName"))
     var authorNames: [String] = []

with

var authorNames: [String] = []

which assumes that the SwiftData's encoding of a string array is identical to CoreData's use of the ValueTransformer in this situation.

If true, this is an ideal solution to my problem.

Can anyone confirm?