Core Data in iOS 10

Episode Links

NSPersistentContainer

let container = NSPersistentContainer(name: "Episodes")

container.loadPersistentStores { (storeDescription, error) in

    container.viewContext.automaticallyMergesChangesFromParent = true
    try! container.viewContext.setQueryGenerationFrom(.current)

    if let e = error {
        print("Error: \(e)")
    } else {
        print("Core data loaded: \(storeDescription)")
    }
}

Fetching Existing Records

Generated models now produced strongly typed fetch requests:

let fetchRequest: NSFetchRequest<Episode> = Episode.fetchRequest()
let existingEpisodes = try! fetchRequest.execute()
let existingEpisodeLookup = existingEpisodes.reduce([:], { (lookup, episode) -> [Int:Episode] in
    var mutableLookup = lookup
    mutableLookup[Int(episode.id)] = episode
    return mutableLookup
})

Insert or Update Records in the Background

container?.performBackgroundTask { moc in
   episodes.forEach { jsonEpisode in
       let model = existingEpisodeLookup[jsonEpisode.id] ?? Episode(context: moc)
       model.id = Int32(jsonEpisode.id)
       model.title = jsonEpisode.title
       model.summary = jsonEpisode.summary
       model.thumbnailURLValue = jsonEpisode.thumbnailURLValue
   }

   try! moc.save()
}

Merging Changes Automatically

First, we set our view context to merge changes from the store, and pin changes to .current to always see the latest data.

container.viewContext.automaticallyMergesChangesFromParent = true
try! container.viewContext.setQueryGenerationFrom(.current)

When the save happens on another context, it gets performed on the store, which will merge changes on the view context. Our fetched results controller detects this change and notifies its delegate:


extension ViewController : NSFetchedResultsControllerDelegate {
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        loadFromCoreData()
    }
}