In my app, an AudioFile has a one to many relationship with UpNextItem. I realised that NSBatchInsertRequest can’t handle relationships at all which is a huge drawback.

How do I handle associating each up next item to their respective audio file without high cpu usage and blocking the main thread especially since I am expecting there to be over 10k to 100k up next items?

Task {
                                let upNextItemsContext = DataController.shared.createNewBackgroundContext()
                                
                                var objects: [[String: Any]] = []
                                
//Delete old up next items on disk

                                await upNextItemsContext.perform {
                                    let deleteRequest = NSBatchDeleteRequest(fetchRequest: UpNextItem.fetchRequest())
                                    if let batchDeleteResult = try? upNextItemsContext.execute(deleteRequest) as? NSBatchDeleteResult, let success = batchDeleteResult.result as? Bool, success {
                                        return
                                    }
                                }
                                
                                await upNextItemsContext.perform {
                                    var index = 0
                                    audioFiles.forEach {
                                        defer {
                                            index += 1
                                        }
                                        
                                        let properties: [String: Any] = [
                                            "name": $0.wrappedName,
                                            "artist": $0.wrappedArtist,
                                            "fileExtension": $0.wrappedFileExtension,
                                            "index": index,
                                            "id": UUID()
                                        ]
                                        
                                        objects.append(properties)
                                    }
                                    
                                    let insertRequest = NSBatchInsertRequest(entity: UpNextItem.entity(), objects: objects)
                                    insertRequest.resultType = .objectIDs
                                    
                                    do {
                                        let result = try upNextItemsContext.execute(insertRequest) as? NSBatchInsertResult
                                        let objectIDArray = result?.result as? [NSManagedObjectID]
                                        let changes = [NSInsertedObjectsKey : objectIDArray]
                                        NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes as [AnyHashable : Any], into: [moc])
                                    } catch {
                                        fatalError("Failed to perform batch update: (error)")
                                    }
                                }
                                
                                //Do a second pass over each up next item to associate with the correct audio file. But this is causing like 200% CPU usage and hangs my app for over 2-3 seconds
                                let upNextItems = try? moc.fetch(UpNextItem.fetchRequest())
                                let fetchRequest = AudioFile.fetchRequest()
                                upNextItems?.forEach { upNextItem in
                                    let namePredicate = NSPredicate(format: "name = %@", upNextItem.wrappedName)
                                    let fileExtensionPredicate = NSPredicate(format: "fileExtension = %@", upNextItem.wrappedFileExtension)
                                    
                                    fetchRequest.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: [namePredicate, fileExtensionPredicate])
                                    let audioFile = try? moc.fetch(fetchRequest)
                                    upNextItem.audioFile = audioFile?.first
                                }
                                
                                try? moc.save() //Save the changes
}