I have a simple entity with identifier (constraint) and name fields. In ViewController I try to add data to the database without worrying about duplicates and there really is no duplicate data in the database, but when I try to get records, I get twice as many of them. As I found out, this only happens when I try to write something to the database, and regardless of whether the attempt was successful, the data goes to my NSFetchRequestResult. What is the reason for this behavior?
DB content now:
ViewController:
class ViewController: UIViewController {
let moc = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
override func viewDidLoad() {
super.viewDidLoad()
//if comment this loop I won't get duplicates
for i in 0...5 {
let ent = Entity(context: moc)
ent.identifier = Int16(i)
ent.name = "Username"
try? moc.save() //if the code is not executed for the first time, then the attempt is unsuccessful due to identifier constraint
}
let fetch = NSFetchRequest<NSFetchRequestResult>(entityName: "Entity")
let fetchedEntities = try? moc.fetch(fetch) as? [Entity]
print(fetchedEntities!.count) // Output: 12 (actually only 6 records in the db)
}
}
Change your code where you create the objects to
for i in 0...5 {
let ent = Entity(context: moc)
ent.identifier = Int16(i)
ent.name = "Username"
}
do {
try moc.save()
} catch {
moc.reset()
}
This way you will remove the faulty (duplicate) objects from the context
Related
I'm working with CloudKit for the first time and am having trouble executing a CKQueryOperation to query all records of a given type. It doesn't help that Apple has deprecated most of the stuff I've found online and that their documentation for these things are completely blank besides the func declaration. I think I've got the "skeleton" of the code done but am unsure of what goes into the .recordMatchedBlock and the .queryResultsBlock.
I have a func queryAllNotes() which should query all records in the public database of type "Notes" and return an array of tuples of the note's title and its associated cloudID, which is just the unique recordName given to it when it is added to the database.
Here's the code for queryAllNotes() :
private func queryAllNotes() -> [(title: String, cloudID: String)] {
/*
query all notes in the cloud DB into an array to populate
the tableView
*/
var resultArray: [(title: String, cloudID: String)] = []
//set the cloud database to .publicCloudDatabase
let container = CKContainer.default()
let cloudDB = container.publicCloudDatabase
let pred = NSPredicate(value: true) //true -> return all records
let query = CKQuery(recordType: "Notes", predicate: pred)
let queryOperation = CKQueryOperation(query: query)
queryOperation.database = cloudDB
queryOperation.resultsLimit = 100
queryOperation.recordMatchedBlock = { (record: CKRecord) in
let noteTitle = record["Title"] as! String
let noteCloudID = record.recordID.recordName
resultArray.append((noteTitle, noteCloudID))
}
queryOperation.queryResultBlock = { (cursor, error) in
}
return resultArray
}
To my understanding the .recordMatchedBlock is called for every record returned by the query so I think it is complete but I could be very wrong. In regards to the .queryResultBlock, my understanding is that the query technically only return one record at a time and this block basically tells the query to run again for the next record for all records within the .resultLimit. How can I structure this query? I am keen to understand what each of these blocks do.
Also this is for a macOS app; I don't know if the code is different for macOS vs iOS but I thought I should include this just in case.
Also I'm getting an error saying "Type of expression is ambiguous without more context" which I'm assuming is because I haven't completed setting up my query. If it's for a different reason could also explain why this is happening.
Edit
I call this func inside of viewDidLoad() like so:
//array var for the array that is used to populate the tableView
var noteRecords: [(title: String, cloudID: String)] = []
override func viewDidLoad() {
super.viewDidLoad()
// do additional setup here
// set serachField delegate
searchField.delegate = self
// set tableView delegate and data source
tableView.delegate = self
tableView.dataSource = self
// load all NoteRecords in public cloud db into noteRecords
noteRecords = queryAllNotes()
}
With the new async pattern it has become much easier to fetch data from CloudKit.
Instead of CKQueryOperation you call records(matching:resultsLimit:) directly and map the result to whatever you like.
A possible error is handed over to the caller.
func queryAllNotes() async throws -> [(title: String, cloudID: String)] {
//set the cloud database to .publicCloudDatabase
let container = CKContainer.default()
let cloudDB = container.publicCloudDatabase
let pred = NSPredicate(value: true) //true -> return all records
let query = CKQuery(recordType: "Notes", predicate: pred)
let (notesResults, _) = try await cloudDB.records(matching: query,
resultsLimit: 100)
return notesResults
.compactMap { _, result in
guard let record = try? result.get(),
let noteTitle = record["Title"] as? String else { return nil }
return (title: noteTitle, cloudID: record.recordID.recordName)
}
}
And use it
override func viewDidLoad() {
super.viewDidLoad()
// do additional setup here
// set serachField delegate
searchField.delegate = self
// set tableView delegate and data source
tableView.delegate = self
tableView.dataSource = self
// load all NoteRecords in public cloud db into noteRecords
Task {
do {
noteRecords = try await queryAllNotes()
tableView.reloadData()
} catch {
print(error)
}
}
}
Please watch the related video from WWDC 2021 for detailed information about the async CloudKit APIs and also the Apple examples on GitHub.
Side note:
Rather than a tuple use a struct. Tuples as data source array are discouraged.
I am using Swift 4 to build a single view iOS 11 application that has a UITableViewController that is also defined as a delegate for a NSFetchedResultsController.
class MyTVC: UITableViewController, NSFetchedResultsControllerDeleagate {
var container:NSPersistentContainer? =
(UIApplication.shared.delegate as? AppDelegate)?.persistentContainer
var frc : NSFetchedResultsController<Student>?
override func viewDidLoad() {
container?.performBackgroundTask { context in
// adds 100 dummy records in background
for i in 1...100 {
let student = Student(context: context)
student.name = "student \(i)"
}
try? context.save() // this works because count is printed below
if let count = try? context.count(for: Student.fetchRequest()) {
print("Number of students in core data: \(count)") // prints 100
}
} // end of background inserting.
// now defining frc:
if let context = container?.viewContext {
let request:NSFetchRequest<Student> = Student.fetchRequest()
request.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)]
frc = NSFetchedResultsController<Student> (
fetchRequest: request,
managedObjectContext: context,
sectionNameKeyPath: nil,
cacheName: nil )
try? frc?.performFetch() // this works and I get no errors
tableView.reloadData()
frc.delegate = self
} // end of frc definition
}
}
If I add one row of Student using the viewContext, the frc will fire the required methods to show it in the tableView. However, the 100 dummy rows are not shown. In fact, If I try to tell the tableview to reload after the insertion is done, my app starts to behave weirdly and becomes buggy, and does not do what it should do (i.e: does not delete rows, does not edit, etc).
But If I restart my app, without calling the dummy insertion, I can see the 100 rows inserted from the previous run.
The only problem is that I can't call tableView.reloadData() from the background thread, so I tried to do this:
// after printing the count, I did this:
DispatchQueue.main.async { [weak self] in
self?.tableView.reloadData() // causes UI to behave weirdly
}
then I tried to call viewContext.perform to reload the table view in the proper thread
func viewDidLoad() {
// code for inserting 100 dummy rows in background thread
// code for defining frc and setting self as delegate
if let context = container?.viewContext {
context.perform { [weak self] in
self?.tableView.reloadData() // that also causes UI to behave weirdly
}
}
}
How can tell my tableview to reload and display the 100 dummy rows in a thread-safe manner?
override func viewDidLoad() {
super.viewDidLoad()
//Always need your delegate for the UI to be set before calling the UI's delegate functions.
frc.delegate = self
//First we can grab any already stored values.
goFetch()
//This chunk just saves. I would consider putting it into a separate function such as "goSave()" and then call that from an event handler.
container?.performBackgroundTask { context in
//We are in a different queue than the main queue, hence "backgroundTask".
for i in 1...100 {
let student = Student(context: context)
student.name = "student \(i)"
}
try? context.save() // this works because count is printed below
if let count = try? context.count(for: Student.fetchRequest()) {
print("Number of students in core data: \(count)") // prints 100
}
//Now that we are done saving its ok to fetch again.
goFetch()
}
//goFetch(); Your other code was running here would start executing before the backgroundTask is done. bad idea.
//The reason it works if you restart the app because that data you didn't let finish saving is persisted
//So the second time Even though its saving another 100 in another queue there were still at least 100 records to fetch at time of fetch.
}
func goFetch() {
if let context = container?.viewContext {
let request:NSFetchRequest<Student> = Student.fetchRequest()
request.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)]
frc = NSFetchedResultsController<Student> (
fetchRequest: request,
managedObjectContext: context,
sectionNameKeyPath: nil,
cacheName: nil )
try? frc?.performFetch()
//Now that records are both stored and fetched its safe for our delegate to access the data on the main thread.
//To me it would make sense to do a tableView reload everytime data is fetched so I placed this inside o `goFetch()`
DispatchQueue.main.async { [weak self] in
self?.tableView.reloadData()
}
}
}
After a lot of reading about the NSFetchedResultsController and the NSPersistentContainer and finally finding an important piece of information here at SO I think I have a working example.
My code is slightly different since I used a project I had for this. Anyway here is what I did:
In my view controller I had a property for my container
private var persistentContainer = NSPersistentContainer(name: coreDataModelName)
And in viewDidLoad I loaded the persistent store and created my 100 records.
persistentContainer.loadPersistentStores { persistentStoreDescription, error in
if let error = error {
print("Unable to add Persistent Store [\(error)][\(error.localizedDescription)]")
} else {
self.createFakeNotes() // Here 100 elements get created
DispatchQueue.main.async {
self.setupView() // other stuff, not relevant
self.fetchNotes() // fetch using fetch result controller
self.tableView.reloadData()
}
}
}
Below is createFakeNotes() where I use a separate context for inserting the elements in a background thread, this code is pretty much taken from Apple's Core Data programming guide but to make the UI being updated I needed to set automaticallyMergesChangesFromParent to true which I found out in this SO answer
I also delete old notes first to make the testing easier.
private func createFakeNotes() {
let deleteRequest = NSBatchDeleteRequest(fetchRequest: Note.fetchRequest())
do {
try persistentContainer.persistentStoreCoordinator.execute(deleteRequest, with: persistentContainer.viewContext)
} catch {
print("Delete error [\(error)]")
return
}
let privateContext = persistentContainer.newBackgroundContext()
privateContext.automaticallyMergesChangesFromParent = true //Important!!!
privateContext.perform {
let createDate = Date()
for i in 1...100 {
let note = Note(context: privateContext)
note.title = String(format: "Title %2d", i)
note.contents = "Content"
note.createdAt = createDate
note.updatedAt = createDate
}
do {
try privateContext.save()
do {
try self.persistentContainer.viewContext.save()
} catch {
print("Fail saving main context [\(error.localizedDescription)")
}
} catch {
print("Fail saving private context [\(error.localizedDescription)")
}
}
}
You should fetch your data by calling it from viewwillappear and then try to reload your tableview.
override func viewWillAppear(_ animated: Bool) {
getdata()
tableView.reloadData()
}
func getdata() {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
do{
persons = try context.fetch(Person.fetchRequest())
}
catch {
print("fetching failed")
}
}
In my application, I have set up a Core Data entity called "Finances". For now it has 2 attributes: money and net-worth.
I wish to write a function that each time it is called, it deletes all results for a specific entity. An example might be:
func resetAttribute(attribute: String) {
}
PS: I have found on the internet a function which was engineered to only delete a specific element of an attribute, which matched to a string. I have modified the code in the following way:
func resetTest() {
if let dataAppDelegatde = UIApplication.shared.delegate as? AppDelegate {
let mngdCntxt = dataAppDelegatde.persistentContainer.viewContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "ApplicationFinances")
let predicate = NSPredicate(format: "money != %#", "vdavduabsdpansuryiubj")
fetchRequest.predicate = predicate
do {
let result = try mngdCntxt.fetch(fetchRequest)
print(result.count)
if result.count > 0 {
for object in result {
print(object)
mngdCntxt.delete(object as! NSManagedObject)
}
}
} catch{
}
}
}
Meaning that if money wouldn't have been equals to vdavduabsdpansuryiubj (Meaning never of course) it would have deleted the other values. But this didn't seem to work.
What happens when you run the function? Does it throw an error? Or does it print just fine and runs fine but nothing actually happens when you reload the core data? If this is the case, try adding:
do {
try mngdCntxt.save()
} catch {}
Right after the for loop is over
To my knowledge, the following code (or very close to it) would retrieve one cloudkit instance from the recordtype array...
let pred = NSPredicate(value: true)
let query = CKQuery(recordType: "Stores", predicate: pred)
publicDatabase.performQuery(query, inZoneWithID: nil) { (result, error) in
if error != nil
{
print("Error" + (error?.localizedDescription)!)
}
else
{
if result?.count > 0
{
let record = result![0]
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.txtDesc.text = record.objectForKey("storeDesc") as? String
self.position = record.objectForKey("storeLocation") as! CLLocation
let img = record.objectForKey("storeImage") as! CKAsset
self.storeImage.image = UIImage(contentsOfFile: img.fileURL.path!)
....(& so on)
However, how and when (physical location in code?) would I query so that I could set each cell to the information of each instance in my DiningType record?
for instance, would I query inside the didreceivememory warning function? or in the cellforRowatIndexPath? or other!
If I am misunderstanding in my above code, please jot it down in the notes, all help at this point is valuable and extremely appreciated.
Without a little more information, I will make a few assumptions about the rest of the code not shown. I will assume:
You are using a UITableView to display your data
Your UITableView (tableView) is properly wired to your viewController, including a proper Outlet, and assigning the tableViewDataSource and tableViewDelegate to your view, and implementing the required methods for those protocols.
Your data (for each cell) is stored in some type of collection, like an Array (although there are many options).
When you call the code to retrieve records from the database (in this case CloudKit) the data should eventually be stored in your Array. When your Array changes (new or updated data), you would call tableView.reloadData() to tell the tableView that something has changed and to reload the cells.
The cells are wired up (manually) in tableView(:cellForRowAtIndexPath:). It calls this method for each item (provided you implemented the tableView(:numberOfRowsInSection:) and numberOfSectionsInTableView(_:)
If you are unfamiliar with using UITableView's, they can seem difficult at first. If you'd like to see a simple example of wiring up a UITableView just let me know!
First, I had to take care of the typical cloudkit requirements: setting up the container, publicdatabase, predicate, and query inputs. Then, I had the public database perform the query, in this case, recordtype of "DiningType". Through the first if statement of the program, if an error is discovered, the console will print "Error" and ending further action. However, if no run-time problem is discovered, each result found to be relatable to the query is appended to the categories array created above the viewdidload function.
var categories: Array<CKRecord> = []
override func viewDidLoad() {
super.viewDidLoad()
func fetchdiningtypes()
{
let container = CKContainer.defaultContainer()
let publicDatabase = container.publicCloudDatabase
let predicate = NSPredicate(value: true)
let query = CKQuery(recordType: "DiningType", predicate: predicate)
publicDatabase.performQuery(query, inZoneWithID: nil) { (results, error) -> Void in
if error != nil
{
print("Error")
}
else
{
for result in results!
{
self.categories.append(result)
}
NSOperationQueue.mainQueue().addOperationWithBlock( { () -> Void in
self.tableView.reloadData()
})
}
}
}
fetchdiningtypes()
I'm trying to insert a default record into my core data entity while the tableview first-time loaded and checked there's no data in the entity.
The data inserted just fine , but the reloadData() didn't work, after navigate to other view and navigate back to the view the data appears. no matter the reloadData() in or out of the .save() method.
override func viewDidLoad() {
let cateContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
let categoryRequest = NSFetchRequest(entityName: "Category")
categoryArray = (try! cateContext.executeFetchRequest(categoryRequest)) as! [Category]
if categoryArray.count == 0 {
let category = NSEntityDescription.insertNewObjectForEntityForName("Category", inManagedObjectContext: cateContext) as! Category
category.sno = "1"
category.category = "General"
category.locate = false
do {
try cateContext.save()
self.categoryTableView.reloadData()
} catch let saveError as NSError {
print("Saving Error : \(saveError.localizedDescription)")
}
}
//self.categoryTableView.reloadData()
}
If your are calling self.categoryTableView.reloadData() in viewDidLoad() method it will not reload your tableView twice. You need to call self.categoryTableView.reloadData() after you have checked if entity existed again.