Swift 3 preload from SQL files in appDelegate - core-data

Question

I am attempting a swift 3 conversion. I was preloading data from sql files in my swift 2 project. I am unsure how to make this work in swift 3.0? Below is my swift 2 appDelegate file. In swift 3 the core data stack has changed enough, that I do not know where to try to reuse the same code that worked for me with swift 2. The code i was using that worked is listed under the comment "added for SQLite preload". Thank you
// MARK: - Core Data stack
lazy var applicationDocumentsDirectory: URL = {
// The directory the application uses to store the Core Data store file. This code uses a directory named "self.edu.SomeJunk" in the application's documents Application Support directory.
let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
return urls[urls.count-1]
}()
lazy var managedObjectModel: NSManagedObjectModel = {
// The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
let modelURL = Bundle.main.url(forResource: "ESLdata", withExtension: "momd")!
return NSManagedObjectModel(contentsOf: modelURL)!
}()
lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
// The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it. This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
// Create the coordinator and store
let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
let url = self.applicationDocumentsDirectory.appendingPathComponent("ESLdata.sqlite")
//ADDED FOR SQLITE PRELOAD
// Load the existing database
if !FileManager.default.fileExists(atPath: url.path) {
let sourceSqliteURLs = [Bundle.main.url(forResource: "ESLdata", withExtension: "sqlite")!,Bundle.main.url(forResource: "ESLdata", withExtension: "sqlite-wal")!, Bundle.main.url(forResource: "ESLdata", withExtension: "sqlite-shm")!]
let destSqliteURLs = [self.applicationDocumentsDirectory.appendingPathComponent("ESLdata.sqlite"), self.applicationDocumentsDirectory.appendingPathComponent("ESLdata.sqlite-wal"), self.applicationDocumentsDirectory.appendingPathComponent("ESLdata.sqlite-shm")]
for index in 0 ..< sourceSqliteURLs.count {
do {
try FileManager.default.copyItem(at: sourceSqliteURLs[index], to: destSqliteURLs[index])
} catch {
print(error)
}
}
}
// END OF ADDED CODE
var failureReason = "There was an error creating or loading the application's saved data."
do {
try coordinator.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: url, options: [NSMigratePersistentStoresAutomaticallyOption:true, NSInferMappingModelAutomaticallyOption:true])
} catch {
// Report any error we got.
var dict = [String: AnyObject]()
dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data" as AnyObject?
dict[NSLocalizedFailureReasonErrorKey] = failureReason as AnyObject?
dict[NSUnderlyingErrorKey] = error as NSError
let wrappedError = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
// Replace this with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog("Unresolved error \(wrappedError), \(wrappedError.userInfo)")
abort()
}
return coordinator
}()
lazy var managedObjectContext: NSManagedObjectContext = {
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
let coordinator = self.persistentStoreCoordinator
var managedObjectContext = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
managedObjectContext.persistentStoreCoordinator = coordinator
return managedObjectContext
}()
// MARK: - Core Data Saving support
func saveContext () {
if managedObjectContext.hasChanges {
do {
try managedObjectContext.save()
print("SAVED")
} catch {
print("Save Failed")
let nserror = error as NSError
NSLog("Unresolved error \(nserror), \(nserror.userInfo)")
abort()
}
}
}
The following is what I attempted to update the code to, and had no luck:
func getDocumentsDirectory()-> URL {
let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
let documentsDirectory = paths[0]
return documentsDirectory
}
// MARK: - Core Data stack
lazy var persistentContainer: NSPersistentContainer = {
/*
The persistent container for the application. This implementation
creates and returns a container, having loaded the store for the
application to it. This property is optional since there are legitimate
error conditions that could cause the creation of the store to fail.
*/
let container = NSPersistentContainer(name: "ESLdata")
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
/*
Typical reasons for an error here include:
* The parent directory does not exist, cannot be created, or disallows writing.
* The persistent store is not accessible, due to permissions or data protection when the device is locked.
* The device is out of space.
* The store could not be migrated to the current model version.
Check the error message to determine what the actual problem was.
*/
fatalError("Unresolved error \(error), \(error.userInfo)")
}
//ADDED FOR SQLITE PRELOAD
let url = self.getDocumentsDirectory().appendingPathComponent("ESLdata.sqlite")
// Load the existing database
if !FileManager.default.fileExists(atPath: url.path) {
let sourceSqliteURLs = [Bundle.main.url(forResource: "ESLdata", withExtension: "sqlite")!,Bundle.main.url(forResource: "ESLdata", withExtension: "sqlite-wal")!, Bundle.main.url(forResource: "ESLdata", withExtension: "sqlite-shm")!]
let destSqliteURLs = [self.getDocumentsDirectory().appendingPathComponent("ESLdata.sqlite"), self.getDocumentsDirectory().appendingPathComponent("ESLdata.sqlite-wal"), self.getDocumentsDirectory().appendingPathComponent("ESLdata.sqlite-shm")]
for index in 0 ..< sourceSqliteURLs.count {
do {
try FileManager.default.copyItem(at: sourceSqliteURLs[index], to: destSqliteURLs[index])
} catch {
print(error)
}
}
}
// END OF ADDED CODE
})
return container
}()
// MARK: - Core Data Saving support
func saveContext () {
let context = persistentContainer.viewContext
if context.hasChanges {
do {
try context.save()
} catch {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
}
}

Answer 1

This seems to be the solution I was looking for. As far as I can tell so far, it works. And sticks the the new slimmer format core data stack for iOS10.
func getDocumentsDirectory()-> URL {
let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
let documentsDirectory = paths[0]
return documentsDirectory
}
// MARK: - Core Data stack
lazy var persistentContainer: NSPersistentContainer = {
let container = NSPersistentContainer(name: "ESLdata")
let appName: String = "ESLdata"
var persistentStoreDescriptions: NSPersistentStoreDescription
let storeUrl = self.getDocumentsDirectory().appendingPathComponent("ESLData.sqlite")
if !FileManager.default.fileExists(atPath: (storeUrl.path)) {
let seededDataUrl = Bundle.main.url(forResource: appName, withExtension: "sqlite")
try! FileManager.default.copyItem(at: seededDataUrl!, to: storeUrl)
}
let description = NSPersistentStoreDescription()
description.shouldInferMappingModelAutomatically = true
description.shouldMigrateStoreAutomatically = true
description.url = storeUrl
container.persistentStoreDescriptions = [description]
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
return container
}()

Answer 2

First of all-- the changes you have made are only partly about Swift 3. You are not required to use NSPersistentContainer, and doing so is a completely different issue from using Swift 3. You can still use all the same Core Data classes and methods as in Swift 2, but with different syntax. If you understand your older code, you're probably better off keeping the same logic and classes but with newer syntax.
If you do switch to NSPersistentContainer, the loadPersistentStores method is more or less comparable to the addPersistentStore call in your older code. When you call that method, the persistent store file is loaded, so it must exist if you want to use its data. In your older code you copy your pre-loaded data before loading the persistent store, but in your newer code you're doing it afterward. That's why you're not seeing the data.
Since you appear to be using the same default store file name that NSPersistentContainer will assume, that's probably enough. If it still doesn't find the data, you may need to create an NSPersistentStoreDescription to tell your container where to put the store file.
But if I were you I'd stick with the older approach and the newer Swift 3 syntax.