CoreData CRUD operations testing and no NSManagedObjectDidSave notification - ios

Question

I have method inserting some object into Core Data storage
func insert(_ e: Entity, completion: #escaping (Result<Entity, Error>) -> Void) {
storage.persistentContainer.performBackgroundTask { [weak self] context in
guard let self = self else { return }
}
}
I have also such test case and only last changeExpectation fails as not receiving this notification.
func test_whenMovieSaved_shouldBeRetrivable() {
// given
let dao = MoviesDao(storage: storage)
let movie = Movie(id: 1, title: "Test Title", posterPath: nil, overview: "Test Details", releaseDate: nil)
let insertExpectation = self.expectation(description: "Should insert entity.")
let loadExpectation = self.expectation(description: "Should load entity.")
let changeExpectation = self.expectation(forNotification: .NSManagedObjectContextDidSave, object: storage.persistentContainer.viewContext, handler: nil)
// when
dao.insert(movie) { (result) in
guard let e = try? result.get() else {
XCTFail("Should get valid entity back.")
return
}
XCTAssertEqual(movie, e)
insertExpectation.fulfill()
dao.load(id: "\(movie.id)") { result in
guard let e = try? result.get() else {
XCTFail("Should load valid entity back.")
return
}
XCTAssertEqual(movie, e)
loadExpectation.fulfill()
}
}
// then
wait(for: [insertExpectation, loadExpectation], timeout: 0.2)
wait(for: [changeExpectation], timeout: 2)
}
I have even tried to add something like this but it didn't force notification to send
self.storage.saveContext(context)
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: [NSInsertedObjectsKey: insertedObjectIds], into: [self.storage.persistentContainer.viewContext])
completion(.success(e))
I also have something like this while creating persistentCoordinator
container.viewContext.mergePolicy = NSMergePolicy.mergeByPropertyObjectTrump
container.viewContext.undoManager = nil
container.viewContext.shouldDeleteInaccessibleFaults = true
container.viewContext.automaticallyMergesChangesFromParent = true

Answer 1

I think I have finally found the solution to this problem. It was in stack.saveContext(context) method as I am using performBackgroundTask { context in
it requires to not only background context.save() to be called but also viewContext.save() should be called.
In my CoreDataStack now I have such methods
func saveContextAsync(_ context: NSManagedObjectContext) {
guard context != mainContext else {
saveContext()
return
}
context.perform {
do {
try context.save()
} catch let error as NSError {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
self.saveContextAsync(self.mainContext)
}
}
func saveContext(_ context: NSManagedObjectContext) {
guard context != mainContext else {
saveContext()
return
}
context.performAndWait {
do {
try context.save()
} catch let error as NSError {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
self.saveContext(self.mainContext)
}
}
func saveContextAsync() {
let context = mainContext
// Save all the changes just made and reset the context to free the cache.
context.perform {
do {
try context.save()
} catch {
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
// Reset the context to clean up the cache and low the memory footprint.
context.reset()
}
}
func saveContext() {
let context = mainContext
// Save all the changes just made and reset the context to free the cache.
context.performAndWait {
do {
try context.save()
} catch {
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
// Reset the context to clean up the cache and low the memory footprint.
context.reset()
}
}