Database is not recreated in Xcode Previews

[pro100filipp]

Description

When using it in preview, it seems the database is preserved between preview runs, not recreated anew. It clearly exists in memory (not on disk), and the context shows we are inside the preview.

This is evident because when the preview is run again, the console shows a unique constraint violation error on the table. In other words, the database already exists and contains the corresponding record.

SQLite error 19: UNIQUE constraint failed: examples.id - while executing `INSERT INTO "examples" ("id", "name") VALUES (?, ?)`

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• I have determined whether this bug is also reproducible in a vanilla GRDB project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

I expect that, similar to SwiftData, if we use an in-memory database, it will be recreated each time we run the preview.

Actual behavior

The database exists and is not recreated.

Reproducing project

SqliteDataPreview.zip

SQLiteData version information

1.6.1

Sharing version information

2.8.0

GRDB version information

7.10.0

Destination operating system

iOS 26

Xcode version information

Version 26.4

Swift Compiler version information

swift-driver version: 1.148.6 Apple Swift version 6.3 (swiftlang-6.3.0.123.5 clang-2100.0.123.102)
Target: arm64-apple-macosx26.0

[mbrandonw]

Hi @pro100filipp, this is just how previews work. They can execute multiple times in the same process. To work around this fact you can use stable IDs for all of your seed data and perform upsets instead of inserts.

Since this isn't an issue with the library I am going to convert it to a discussion. Please feel free to continue the conversation over there!

[pro100filipp]

Thanks for the clarification. To be honest, I'm currently using TRUNCATE on my tables to seed the database for previews, but the upsert approach definitely looks more elegant.

I still have a question, though: why does this work in SwiftData? Here is an example of some simple code used in a preview where repeated runs don't result in duplicate entities. It seems like the container is being recreated every time.

import SwiftData

@Model
class Example {
    var title: String
    init(title: String) {
        self.title = title
    }
}

struct ExampleView: View {
    @Query private var examples: [Example] = []
    
    var body: some View {
        List(examples) {
            Text($0.title)
        }
    }
}

#Preview {
    let container = try! ModelContainer(for: Example.self, configurations: .init(isStoredInMemoryOnly: true))
    container.mainContext.insert(Example(title: "asd"))
    container.mainContext.insert(Example(title: "qwe"))
    
    return ExampleView()
        .modelContainer(container)
}

I suspect that the issue with SQLiteData is due to our use of Swift Dependencies. My thoughts are that the database created during bootstrapDatabase is staying in the cache, I would, however, be grateful for your comments on this.