Document-based SwiftData apps fail to identify a store on iPad?

Question

Created Jun ’24

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When trying to run my document-based iPad app using iPadOS 18 beta and Xcode 16 beta, I get an error like the following after opening a document:

Thread 1: Fatal error: Failed to identify a store that can hold instances of SwiftData._KKMDBackingData<MyProject.MyModel> from [:]

In order to help track down what is going wrong, I downloaded the sample app from WWDC23 session "Build an app with SwiftData" found here: https://developer.apple.com/documentation/swiftui/building-a-document-based-app-using-swiftdata

When I try to run the end-state of that sample code, I get a similar error when running the app on my iPad and creating a new deck:

Thread 1: Fatal error: Failed to identify a store that can hold instances of SwiftData._KKMDBackingData<SwiftDataFlashCardSample.Card> from [:]

Given that the sample project is generating the same error as my own project, is this a problem with SwiftData and document-based apps in general? Or is there a change of approach that I should try?

Answered by DTS Engineer in 806617022

Thread 1: Fatal error: Failed to identify a store that can hold instances of SwiftData._KKMDBackingData<SwiftDataFlashCardSample.Card> from [:] ... It did not happen with the first document I created, but re-opening that document reveals that nothing saved. The second document did save changes, but it resulted in this error on close.

I'd like to confirm that the relevant engineering team can now reproduce the issue described above, thanks to @litkyle, and is actively working on it. The issue is tracked with FB13950404 (or r.130044320 internally).

For the "no location available to save 'Untitled.sampledeck'" error, I saw it when running the app in a simulator, but not on a device, as I mentioned above. This issue may be relevant to FB13950404, but I am not completely sure if it is exactly the same, and so would suggest that you file a new feedback report so it doesn't get missed – If you do so, please share your report ID here.

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.

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Answer 1

DTS Engineer OP

Apple

Oct ’24

Traditionally, UI/NSDocument-based architecture handles autosave pretty well, and I don't think DocumentGroup + SwiftData should be an exception in this regard.

As of today though, it seems that there is a bug related to SwiftData autosave, as discussed in the Xcode 16 MacOS Sequoia SwiftData not saving data after running application post.

Though you can probably work around the issue by explicitly saving the model context after making a change, I’d suggest that you file a feedback report against that autosave doesn't work in DocumentGroup + SwiftData – If you do so, please share your report ID here for folks to track.

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.

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Answer 2

eduserve OP

1w

I had this error too. Turned out that I was missing one of my models in my ModelConfiguration's schema. Once I added the missing model to the schema, error went away.

let schema = Schema([Person.self, Car.self, City.self])
        let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false)

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