I am having a syntax issues I just cannot figure out. I do not have a strong Swift back ground, so the answer my be easy (I hope.) So, here is the snippet:
public func getLatestDate()-> NSDate? {
var request = NSFetchRequest()
var entity = NSEntityDescription.entityForName("Event", inManagedObjectContext: self.managedObjectContext)
request.entity = entity
let sortDescriptor = NSSortDescriptor(key: "timeStamp", ascending: false)
let sortDescriptors = [sortDescriptor]
request.sortDescriptors = sortDescriptors
var error: NSError? = nil
do {
let results = try self.managedObjectContext.executeFetchRequest(request)
} catch {
fatalError("Failed to fetch employees: \(error)")
}
var date: NSDate?
if results != nil {
let managedObject: NSManagedObject = results![0] as NSManagedObject
date = managedObject.valueForKey("timeStamp") as? NSDate
}
return date
}
The problem is that if results != nil and the results on the following line are throwing an error stating:
Use of unresolved identifier 'results'
How do I resolve this issue?
Thank you.
-Matt
You're declaring results here:
do {
let results = try self.managedObjectContext.executeFetchRequest(request)
} catch {
fatalError("Failed to fetch employees: \(error)")
}
So you can see that it's being done within a do-catch block. That means that where you try to use it is out of the scope where it was defined, so it can't see it at all. By the time you get to if results != nil, it's already gone out of scope and is gone.
in addition to Gavin: this will work cause of the reason, thar Gavin mentioned
do {
let results = try self.managedObjectContext.executeFetchRequest(request)
if results != nil {
let managedObject: NSManagedObject = results![0] as NSManagedObject
date = managedObject.valueForKey("timeStamp") as? NSDate
}
} catch {
fatalError("Failed to fetch employees: \(error)")
}
Related
I have a list of object:
#FetchRequest(entity: ObjectDetail.entity(), sortDescriptors: []) var myObject: FetchedResults<ObjectDetail>
My ObjectDetail is an Entity in my .xcdatamodel with a structure like this:
listOfObject: Transformable (List of custom object)
objectId: UUID
objectName: String
objectDescription: String
ListOfObject:
public class ListOfObject: NSObject, NSCoding, ObservableObject {
...
}
I'm trying to update an element inside my listOfObject.
Here are 3 approaches I tried so far:
First approach:
mangedObjectContext.performAndWait {
self.elementFromListOfObject.objectWillChange.send()
elementFromListOfObject.weight = 0
try? mangedObjectContext.save()
}
Second approach:
if let selectedObject = self. myObject.first(where: {$0.objectName == self.currentSelectedObjectName}) {
if let selectedElementFromListOfObject = selectedObject.myList?.myListOfObject.first(where: {$0 == self.currentSelectedObject }) {
selectedElementFromListOfObject.weight = 0
self.excercise.objectWillChange.send()
saveContext()
}
}
Third approach
do {
let request = NSBatchUpdateRequest(entity: ObjectDetail.entity())
request.resultType = .updatedObjectIDsResultType
request.propertiesToUpdate = ["weight": 0]
let result = try mangedObjectContext.execute(request) as? NSBatchUpdateResult
let objectIDArray = result?.result as? [NSManagedObjectID]
let changes = [NSUpdatedObjectsKey: objectIDArray]
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes as [AnyHashable : Any], into: [mangedObjectContext])
} catch {
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
The third one crashed because it says request.propertiesToUpdate is null, the other approaches save the value, but when I restart the app its the default one.
What is the best approach to update a value in Core Data in SwiftUI?
hello community I am a novice and this is my first question.
how to change all the attributes of an entity and be able to change all my Core Data elements,
because I can only change the first attribute of an entity but not all my data records.
Here in this function I can only change the name
and then I get this following error has the line:
let objectUpdate = test[0] : Thread 1: Fatal error: Index out of range
func updateData() {
var newName = ""
var newPrenom = ""
newName = name.text!
newPrenom = prenom.text!
let managedContext = AppDelegate.viewContext
let fetchRequest : NSFetchRequest<NSFetchRequestResult> = NSFetchRequest.init(entityName: "Person")
fetchRequest.predicate = NSPredicate(format: "name = %#", newName)
do {
fetchRequest.predicate = NSPredicate(format: "prenom = %#", newPrenom)
let test = try! managedContext.fetch(fetchRequest) as! [NSManagedObject]
let objectUpdate = test[0]
objectUpdate.setValue(newName,forKey: "name")
objectUpdate.setValue(newPrenom, forKey: "prenom")
do {
try managedContext.save()
}
catch {
print(error)
}
} catch {
print(error)
}
}
There are a number of ways we can avoid this error.
Unwrapping optional .first value
Swift's Collection gives us safe way to get first item, simply by accessing the first property on a given collection. It will return an Optional<Element> value so we need to unwrap it first either by using if let of guard let
if let object = test.first {
// do something with object
}
or
guard let object = test.first else { return }
// do something with object
Checking if value at index exists
It's often a good idea to check for a specific index within the indices property before accessing the value behind it.
if test.indices.contains(0) {
let object = test[0]
// do something with object
}
These hints should prevent your code from crashing again.
Other Suggestions
This is not really safe or clean:
var newName = ""
var newPrenom = ""
newName = name.text!
newPrenom = prenom.text!
We can make it much cleaner and most importantly safer by using a guard statement
guard let newName = name.text, let newPrenom = prenom.text else { return }
Two important things happened here:
No more force-unwrapping the optional values of text [which could cause a crash]
The properties are now immutable, meaning we can be sure that what we are saving to the CoreDate is what was retreived at the beginning of the function
Since the line:
let test = try! managedContext.fetch(fetchRequest) as! [NSManagedObject]
is already wrapped in the do-catch clause, you can safely remove forced try! and replace it with try.
let test = try managedContext.fetch(fetchRequest) as! [NSManagedObject]
Let's use types! On this line you create a NSFetchRequest object for some entity named "Person".
let fetchRequest : NSFetchRequest<NSFetchRequestResult> = NSFetchRequest.init(entityName: "Person")
I am guessing CoreData have generated for you a NSManagedObject subclass, named Person. If this is true, you could rewrite it like this:
let fetchRequest = NSFetchRequest<Person>(entityName: "Person")
With the previous tip implemented, we can now get rid of as! [NSManagedObject] from this line:
let test = try managedContext.fetch(fetchRequest) as! [NSManagedObject]
Since the NSFetchRequest object is now nicely typed, we can take advantage of it by rewriting it like this:
let test: [Person] = try managedContext.fetch(fetchRequest)
So we are using proper types now? cool! Lets now improve this:
objectUpdate.setValue(newName,forKey: "name")
objectUpdate.setValue(newPrenom, forKey: "prenom")
by rewriting this and using properties on Person object
objectUpdate.name = newName
objectUpdate.prenom = newPrenom
No need for introducing second level of do-catch clause, since we are already in one!
do {
try managedContext.save()
}
catch {
print(error)
}
you can easily replace it with just the save() call, like this:
try managedContext.save()
Are you sure these predicates are what you want?
fetchRequest.predicate = NSPredicate(format: "name = %#", newName)
fetchRequest.predicate = NSPredicate(format: "prenom = %#", newPrenom)
What I can read from them is that you are fetching Person object where the name is newName and prenom is newPrenom and then you update it with the same exact values? Are you using some kind of identification of users? like id: Int or id: UUID? It would make much more sense to write something like this
let id: Int = // ID of the user you are currently editing
fetchRequest.predicate = NSPredicate(format: "id == \(id)")
if you are not using any id's, you could try storing the initial values of name and prenom
// in cell declaration - set when you configure your cell
var initialName: String?
var initialPrenom: String?
// then in your function:
fetchRequest.predicate = NSPredicate(format: "name = %#", initialName)
fetchRequest.predicate = NSPredicate(format: "prenom = %#", initialPrenom)
But I just noticed you also override you first predicate with the second one. You need to use NSCompoundPredicate
fetchRequest.predicate = NSCompoundPredicate(
type: .and, subpredicates: [
NSPredicate(format: "name = %#", initialName),
NSPredicate(format: "prenom = %#", initialPrenom)
]
)
Suggested version
func updateData() {
guard let newName = name.text, let newPrenom = prenom.text else { return }
let managedContext = AppDelegate.viewContext
let fetchRequest = NSFetchRequest<Person>(entityName: "Person")
fetchRequest.predicate = NSCompoundPredicate(
type: .and, subpredicates: [
NSPredicate(format: "name = %#", initialName),
NSPredicate(format: "prenom = %#", initialPrenom)
]
)
do {
let objects: [Person] = try managedContext.fetch(fetchRequest)
guard let object = objects.first else { return }
object.name = newName
object.prenom = newPrenom
try managedContext.save()
} catch {
print(error)
}
}
If the index 0 is out of range, it means that the array is empty. Before accessing it, add
if test.isEmpty{
return //the fetch request didn't return any values
}
I have the following entities and relationship
I want to be able to set an exercise to have a nil result for its routine name relationship, if that makes sense? so that it can later be set as a routine name when the routine entity is formed.
My question is, how do you set this sort of attribute up? I am trying the following code but it causes a fatal crash:
userExercise.usersroutine?.name = nil
My logic being that i take the exercise and follow the relationship to the name property and set it to nil?
Thanks for any correction and clarification on my logic
EDIT: Added my existing exercise and routine save functions
func createExercise() {
guard let managedObjectContext = managedObjectContext else { return }
if let userExercise = userExercise {
userExercise.name = userExerciseName.text
userExercise.sets = Int64(userSetsCount)
userExercise.reps = Int64(userRepsCount)
userExercise.weight = Double(self.userExerciseWeight.text!)!
userExercise.id = UUID().uuidString
userExercise.routine = nil
}
do {
try managedObjectContext.save()
} catch {
fatalError("Failure to save context: \(error)")
}
}
Routine Creation:
func createRoutine() {
guard let managedObjectContext = managedObjectContext else { return }
let userRoutine = UserRoutine(context: managedObjectContext)
userRoutine.name = workoutNameTextfield.text
do {
try managedObjectContext.save()
} catch {
fatalError("Failure to save context: \(error)")
}
}
Current Fetch Request:
fileprivate lazy var fetchedResultsController: NSFetchedResultsController<UserExercise> = {
let fetchRequest: NSFetchRequest<UserExercise> = UserExercise.fetchRequest()
fetchRequest.sortDescriptors = [NSSortDescriptor(key: "id", ascending: true)]
let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
fetchedResultsController.delegate = self
return fetchedResultsController
Please check the implementation below I'have created some exercises and routines. Also read comments in code, this will help you figure out how to go about it.
Function to add a new exercise
func createExercise(weight: Int16, respetitions: Int16, name: String, routine: Routine?)->Exercise? {
let context = getMainContext()
let exercise = NSEntityDescription.insertNewObject(forEntityName: "Exercise", into: context) as! Exercise
exercise.setValue(weight, forKey: "weight")
exercise.setValue(name, forKey: "name")
exercise.setValue(respetitions, forKey: "rep")
do {
try context.save()
return exercise
}
catch
{
fatalError("unable to Ssavve")
}
}
Function to add a new routine
func createRoutine(name: String, exercises:[Exercise]) {
let context = getMainContext()
let routine = NSEntityDescription.insertNewObject(forEntityName: "Routine", into: context) as! Routine
routine.name = name
//Iterate over Exercise objects & check if routine is nil.
//Here if routine is not nil it menas your exercise is already assigned to a routine.
//If routine is nil assign routine.addToRelationship(<#T##value: Exercise##Exercise#>) and Also assign routine to the execise.
do {
try context.save()
}
catch
{
fatalError("unable to Ssavve")
}
}
Function to get main NSManagedObjectContext on which we can perform core-data actions
func getMainContext() -> NSManagedObjectContext {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
return appDelegate.persistentContainer.viewContext
}
Below, First I create few exercises without any relationship to routines
"The routine doesnt exist when the exercises are created, it is created afterward and its name is set"
and then create routines by passing some exercises (You can refer to other answer on how to fetch exercises with routine as nil values)
func initializer() {
//I'm adding exercises first without routines
let ex1 = self.createExercise(weight: 10, respetitions: 4, name: "Exercise1", routine: nil)
let ex2 = self.createExercise(weight: 5, respetitions: 10, name: "Exercise2", routine: nil)
let ex3 = self.createExercise(weight: 20, respetitions: 2, name: "Exercise3", routine: nil)
let ex4 = self.createExercise(weight: 5, respetitions: 10, name: "Exercise2", routine: nil)
self.createRoutine(name: "Routine 1", exercises: [ex1!, ex2!]) //You can pass all the exercises or use fetch request to query exercises with routine as nil
self.createRoutine(name: "Routine 2", exercises: [ex3!, ex4!])
self.createRoutine(name: "Routine 3", exercises: [ex1!, ex2!]) //This routine shall not be adding any execises as they are already added to othe routines
}
Updating create routine Function to query results of UserExercise which has usersroutine as nil
func createRoutine() {
guard let managedObjectContext = managedObjectContext else { return }
let userRoutine = UserRoutine(context: managedObjectContext)
userRoutine.name = workoutNameTextfield.text
//Getting nil value User Exercises
let request: NSFetchRequest<UserExercise> = UserExercise.fetchRequest()
request.predicate = NSPredicate(format: "usersroutine == nil")
do {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
let queryResults = try context.fetch(request)
//I like to check the size of the returned results!
print ("num of results = \(queryResults.count)")
//You need to convert to NSManagedObject to use 'for' loops
for exercise in queryResults as [NSManagedObject] {
//get the Key Value pairs (although there may be a better way to do that...
print("Exercise NAME: \(exercise.value(forKey: "name"))")
}
} catch {
print("Error with request: \(error)")
}
do {
try managedObjectContext.save()
} catch {
fatalError("Failure to save context: \(error)")
}
}
It doesn't seem that you should need to use the name attribute at all. This attribute should be used for storing the actual name of the UserRoutine and not for anything relationship based.
The relationships between entities in Core Data don't rely on a particular attribute of an entity, but between the entities themselves.
"I want the routine builder to look at the exercises and import all the exercises with nil in the relationship into it"
So...
Create a fetch request to fetch all the entities of UserExercise that don't have a related UserRoutine (i.e. where userroutine is nil).
let orphanedExerciseFetchRequest = NSFetchRequest(entityName: "UserExercises")
orphanedExerciseFetchRequest.predicate = NSPredicate(format: "userroutine == nil)
Execute this fetch request to get an array of UserExercises (with no related routine)
let orphanedExercises = managedObjectContext.executeFetchRequest(orphanedExerciseFetchRequest())
"creating a routine with attributed exercises"
Set the fetched UserExercise entitiy's property userRoutine to your routine (and don't forget to save the changes in your managed object context).
myRoutine.userexercises = orphanedExercises
Later, if you want to get the exercises for a particular routine:
let fetchRequest = NSFetchRequest(entityName: "UserExercises")
fetchRequest.predicate = NSPredicate(format: "userroutine == %#", someUserRoutine)
In Swift 2 the following code was working:
let request = NSFetchRequest(entityName: String)
but in Swift 3 it gives error:
Generic parameter "ResultType" could not be inferred
because NSFetchRequest is now a generic type. In their documents they wrote this:
let request: NSFetchRequest<Animal> = Animal.fetchRequest
so if my result class is for example Level how should I request correctly?
Because this not working:
let request: NSFetchRequest<Level> = Level.fetchRequest
let request: NSFetchRequest<NSFetchRequestResult> = Level.fetchRequest()
or
let request: NSFetchRequest<Level> = Level.fetchRequest()
depending which version you want.
You have to specify the generic type because otherwise the method call is ambiguous.
The first version is defined for NSManagedObject, the second version is generated automatically for every object using an extension, e.g:
extension Level {
#nonobjc class func fetchRequest() -> NSFetchRequest<Level> {
return NSFetchRequest<Level>(entityName: "Level");
}
#NSManaged var timeStamp: NSDate?
}
The whole point is to remove the usage of String constants.
I think i got it working by doing this:
let request:NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "Level")
at least it saves and loads data from DataBase.
But it feels like it is not a proper solution, but it works for now.
The simplest structure I found that works in 3.0 is as follows:
let request = NSFetchRequest<Country>(entityName: "Country")
where the data entity Type is Country.
When trying to create a Core Data BatchDeleteRequest, however, I found that this definition does not work and it seems that you'll need to go with the form:
let request: NSFetchRequest<NSFetchRequestResult> = Country.fetchRequest()
even though the ManagedObject and FetchRequestResult formats are supposed to be equivalent.
Here are some generic CoreData methods that might answer your question:
import Foundation
import Cocoa
func addRecord<T: NSManagedObject>(_ type : T.Type) -> T
{
let entityName = T.description()
let context = app.managedObjectContext
let entity = NSEntityDescription.entity(forEntityName: entityName, in: context)
let record = T(entity: entity!, insertInto: context)
return record
}
func recordsInTable<T: NSManagedObject>(_ type : T.Type) -> Int
{
let recs = allRecords(T.self)
return recs.count
}
func allRecords<T: NSManagedObject>(_ type : T.Type, sort: NSSortDescriptor? = nil) -> [T]
{
let context = app.managedObjectContext
let request = T.fetchRequest()
do
{
let results = try context.fetch(request)
return results as! [T]
}
catch
{
print("Error with request: \(error)")
return []
}
}
func query<T: NSManagedObject>(_ type : T.Type, search: NSPredicate?, sort: NSSortDescriptor? = nil, multiSort: [NSSortDescriptor]? = nil) -> [T]
{
let context = app.managedObjectContext
let request = T.fetchRequest()
if let predicate = search
{
request.predicate = predicate
}
if let sortDescriptors = multiSort
{
request.sortDescriptors = sortDescriptors
}
else if let sortDescriptor = sort
{
request.sortDescriptors = [sortDescriptor]
}
do
{
let results = try context.fetch(request)
return results as! [T]
}
catch
{
print("Error with request: \(error)")
return []
}
}
func deleteRecord(_ object: NSManagedObject)
{
let context = app.managedObjectContext
context.delete(object)
}
func deleteRecords<T: NSManagedObject>(_ type : T.Type, search: NSPredicate? = nil)
{
let context = app.managedObjectContext
let results = query(T.self, search: search)
for record in results
{
context.delete(record)
}
}
func saveDatabase()
{
let context = app.managedObjectContext
do
{
try context.save()
}
catch
{
print("Error saving database: \(error)")
}
}
Assuming that there is a NSManagedObject setup for Contact like this:
class Contact: NSManagedObject
{
#NSManaged var contactNo: Int
#NSManaged var contactName: String
}
These methods can be used in the following way:
let name = "John Appleseed"
let newContact = addRecord(Contact.self)
newContact.contactNo = 1
newContact.contactName = name
let contacts = query(Contact.self, search: NSPredicate(format: "contactName == %#", name))
for contact in contacts
{
print ("Contact name = \(contact.contactName), no = \(contact.contactNo)")
}
deleteRecords(Contact.self, search: NSPredicate(format: "contactName == %#", name))
recs = recordsInTable(Contact.self)
print ("Contacts table has \(recs) records")
saveDatabase()
This is the simplest way to migrate to Swift 3.0, just add <Country>
(tested and worked)
let request = NSFetchRequest<Country>(entityName: "Country")
Swift 3.0 This should work.
let request: NSFetchRequest<NSFetchRequestResult> = NSManagedObject.fetchRequest()
request.entity = entityDescription(context)
request.predicate = predicate
I also had "ResultType" could not be inferred errors. They cleared once I rebuilt the data model setting each entity's Codegen to "Class Definition". I did a brief writeup with step by step instructions here:
Looking for a clear tutorial on the revised NSPersistentContainer in Xcode 8 with Swift 3
By "rebuilt" I mean that I created a new model file with new entries and attributes. A little tedious, but it worked!
What worked best for me so far was:
let request = Level.fetchRequest() as! NSFetchRequest<Level>
I had the same issue and I solved it with the following steps:
Select your xcdatamodeld file and go to the Data Model Inspector
Select your first Entity and go to Section class
Make sure that Codegen "Class Definition" is selected.
Remove all your generated Entity files. You don't need them anymore.
After doing that I had to remove/rewrite all occurences of fetchRequest as XCode seem to somehow mix up with the codegenerated version.
HTH
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
func loadItemsCategory() {
let request: NSFetchRequest<Category> = Category.fetchRequest()
do {
categoryArray = try context.fetch(request)
} catch {
print(error)
}
tableView.reloadData()
}
My fetch request is returning nil from an entity that I think I've successfully put data into and after hours and hours of debugging, I haven't been able to figure it out. (Disclaimer: I've looked at the countless threads here on SO that talk about fetch requests and unwrapping options but every one I found is about how to deal with the unwrapping error. I'm asking for help figuring out why my fetch request isn't returning a record when I believe it should.)
In the view controller where I'm going to display the data, I have this in viewWillAppear:
class LiftLogTableViewController: UITableViewController {
var managedObjectContext: NSManagedObjectContext!
var liftEvents = [LiftEvent]()
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
let fetchRequest = NSFetchRequest(entityName: "LiftEvent")
do {
if let results = try managedObjectContext.executeFetchRequest(fetchRequest) as? [LiftEvent] {
liftEvents = results <---- nil error happening here
}
} catch {
fatalError("Error fetching data!")
}
}
But I believe there's a record in there because in AppDelegate.addData() I've done this:
// create a lift event in LiftEvent
let liftEvent = LiftEvent(entity: liftEventEntity, insertIntoManagedObjectContext: managedObjectContext)
let dateStr = "05-27-2016"
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "MM-dd-yyyy"
let date: NSDate = dateFormatter.dateFromString(dateStr)!
liftEvent.date = date
liftEvent.liftEventUid = 1
liftEvent.liftUid = 1
liftEvent.formulaUid = 1
liftEvent.maxAmount = 250
print("Added lift ID: \(liftEvent.liftEventUid) lift ID: \(liftEvent.liftUid) weight: \(liftEvent.maxAmount) formula: \(liftEvent.formulaUid) ")
saveContext()
}
func saveContext () {
if managedObjectContext.hasChanges {
do {
try managedObjectContext.save()
} catch {
// Replace this implementation 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.
let nserror = error as NSError
NSLog("Unresolved error \(nserror), \(nserror.userInfo)")
abort()
}
}
}
I'm learning CoreData so at this point I have to assume there's something basic I'm just missing.
Thanks in advance.
Assuming you're using the standard Core Data template you need to assign a value to the managedObjectContext property in the LiftLogTableViewController class.
For example in viewDidLoad
override func viewDidLoad() {
super.viewDidLoad()
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
managedObjectContext = appDelegate.managedObjectContext
}
However the recommended way is to pass the context via the segue.