fetchAll returning empty array

[darrenasaro]

I have an app which stores an entity class EntityA: NSManagedObject {...}
I have the following simplified CoreData code to fetch this entity

    let container = NSPersistentContainer(name: "Model")
    let context = container.viewContext
    let coordinator = NSPersistentStoreCoordinator(managedObjectModel: container.managedObjectModel)
    
    let documentsPath = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
    let persistentStoreURL = documentsPath.appendingPathComponent("Model.sqlite")
    
    try! coordinator.addPersistentStore(
      ofType: NSSQLiteStoreType,
      configurationName: nil,
      at: persistentStoreURL,
      options: [:]
    )

    container.loadPersistentStores { _, _ in }
    
    let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "EntityA")
    try! context.fetch(fetchRequest) as! [EntityA] // array populated with multiple objects

I created the equivalent CoreStore code

    let dataStack = DataStack(xcodeModelName: "Model")

    let documentsPath = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
    let sqliteFileUrl = documentsPath.appendingPathComponent("Model.sqlite")
    
    let storage = SQLiteStore(fileURL: sqliteFileUrl)
    try! dataStack.addStorageAndWait(storage)

    try! dataStack.fetchAll(From<ModelA>(nil)) // array empty

The CoreData code returns the properly populated array while CoreStore returns an empty array. I tried initializing SQLiteStore with a number of different options, and tried the async versions of addStorage all to no avail. I set breakpoints in the relevant CoreStore functions, but could not find anything glaring that would indicate the issue. Not sure if this is a bug or if I am misusing CoreStore but any help here would be much appreciated.

[JohnEstropia]

@darrenasaro Since you're not getting an error at try! dataStack.fetchAll(), then it's likely your SQLite file does not contain records in the first place.

[darrenasaro]

It does as evidenced by the CoreData implementation returning a populated array. I've swapped these implementations verbatim with all else equal and the CoreData one always returns a populated array while the CoreStore implementation always returns empty.

[JohnEstropia]

@darrenasaro Can you print the original file URL from here

let persistentStore = try! coordinator.addPersistentStore(
      ofType: NSSQLiteStoreType,
      configurationName: nil,
      at: persistentStoreURL,
      options: [:]
    )
print(persistentStore.url)

and check if it's still the same URL passed to SQLiteStore here?

let sqliteFileUrl = documentsPath.appendingPathComponent("Model.sqlite")

[darrenasaro]

@JohnEstropia They are the same. I've recreated the issue in it's simplest form here
https://github.com/darrenasaro/fetch-demo

[JohnEstropia]

Thanks for isolating the issue! I'll investigate

[JohnEstropia]

@darrenasaro Oh boy... It looks like NSPersistentContainer forces the file directory to where it likes. Try this out:

print("Expected URL:\n\(sqliteFileUrl)")

container.loadPersistentStores { persistentStore, _ in
    print("NSPersistentContainer:\n\(persistentStore.url!)")
}

let store = try! dataStack.addStorageAndWait(storage)
print("CoreStore:\n\(store.fileURL)")

Look at the output:

Expected URL:
file:///Users/<User>/Library/Developer/CoreSimulator/Devices/185DD2F2-A17F-4FBB-9D90-2BDA5B802F57/data/Containers/Data/Application/2732C567-34D7-42EF-942C-2DB5F34CD27F/Documents/Model.sqlite

NSPersistentContainer:
file:///Users/<User>/Library/Developer/CoreSimulator/Devices/185DD2F2-A17F-4FBB-9D90-2BDA5B802F57/data/Containers/Data/Application/2732C567-34D7-42EF-942C-2DB5F34CD27F/Library/Application%20Support/Model.sqlite

CoreStore:
file:///Users/<User>/Library/Developer/CoreSimulator/Devices/185DD2F2-A17F-4FBB-9D90-2BDA5B802F57/data/Containers/Data/Application/2732C567-34D7-42EF-942C-2DB5F34CD27F/Documents/Model.sqlite

Note that NSPersistentContainer moved the directory to Library/Application Support/, while CoreStore keeps it to where it's actually configured (/Documents/).

[JohnEstropia]

It looks like the behavior is correct if you use the NSPersistentStoreDescription method instead:

[JohnEstropia]

Since it looks like CoreStore is behaving correctly here, I'm marking this issue as a ios/compiler bug. I suggest that you find the original path actually created by the NSPersistentContainer for your store, and then pass it to CoreStore in your migrated code. I'd also recommend submitting a bug report to Apple through feedback assistant, since this issue seems destructive enough on its own.

[darrenasaro]

@JohnEstropia Thank you for investigating this! Excited I can use this library now. This CoreData behavior definitely seems to be problematic. I actually downloaded the container to investigate and it looks like CoreData puts an sqlite file in /Documents/(or whatever directory you specify) and Library/Application Support/, the former file having just structure data and the latter containing structure data as well as actual records. Super weird. Will follow with a bug report.

[JohnEstropia]

Oh my, that's even worse. I'll try to explain that situation in the CoreStore README for future migrators. Thanks for investigating the behavior further