I want a "fake" preview NSManagedObject to display as an example. However, I don't want to have it cluttering up my regular context. Here's what I'm assuming could work:
Create a new NSManagedObjectContext and store the preview NSManagedObject there
let moc = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
let person = Person(moc, "Person Name")
What happens to the new context in this case? Is it slowly filling up storage or will it get removed if no save() is called and the View removed?
Remove the newly created NSManagedObject when leaving the view
SomeView()
.onDisappear() {
moc.delete(person)
PersistenceController.shared.save()
}
This might not work if the .onDisappear() function doesn't get called, e.g. when the user leaves the app while that particular view is still open.
Add the fake preview NSMangagedObject to the regular context and filter it out everywhere else (probably the worst idea)
Create a new global context only for fake NSManagedObjects
Not sure which of these options is best or if there's a better way I haven't thought of. Thanks :)
I created a new PersistenceController in memory as Joakim Danielson suggested in the comments, but using it alongside my other context was causing crashes and error messages. Simply creating a new NSManagedObjectContext, however, worked fine.
It is not saved to my "real" context, either (Apple Documentation):
Changes to managed
objects are held in memory, in the associated context, until that
context is saved to one or more persistent stores
let tempMoc = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
Usage
let person = Person(tempMoc, "Person Name")
I want to display data fetched from Core Data in a widget. But #FetchRequest doesn’t work on widgets.
As I understand, we have to create an app group and make a shared persistent container.
What I want to know is how to read (fetch) data on widgets from that shared persistent container or simply, how to display data fetched from Core Data in widgets.
First you need to create an AppGroup which will be used to create a Core Data Persistent Container (here is a good explanation how to do it)
Then you need to create your own CoreData stack (an example can be found when you create a new empty project with CoreData enabled).
Accessing Core Data Stack in MVVM application
Assuming you have already created your Core Data model (here called DataModel), you now need to set the container url to your custom shared container location:
Share data between main App and Widget in SwiftUI for iOS 14
let containerURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: <your_app_group>)!
let storeURL = containerURL.appendingPathComponent("DataModel.sqlite")
let description = NSPersistentStoreDescription(url: storeURL)
let container = NSPersistentContainer(name: "DataModel")
container.persistentStoreDescriptions = [description]
container.loadPersistentStores { ... }
Now you can get the managedObjectContext from your shared Persistent Container:
let moc = CoreDataStack.shared.managedObjectContext
and perform a fetch request with it (more information here)
let predicate = NSPredicate(format: "attribute1 == %#", "test")
let request = NSFetchRequest<SomeItem>(entityName: "SomeItem")
let result = try moc.fetch(request)
Apart from all the links above I recommend you also read this tutorial about Core Data:
Core Data with SwiftUI Tutorial: Getting Started
Here is a GitHub repository with different Widget examples including the Core Data Widget.
For people who did all the work above, and finally can get the connection to your Core Data (e.g. you can get the count of request), but can't fetch the request, is mostly because that the entity you're fetching contains transformable type, and for some reason this error occurred: Cannot decode object of class, try fix this.
Could anyone tell me what the way of storing a long text in a swift app is. Let's suppose I have an app that has a table view and when I chose a row I go to a new scene where I have a big page filled by text.
The question is where do I have to store the data of the table's row and the whole text? And how?
Do I have to make a model? Is it just one for both the table and the text? Or more than one. Is there any tutorial that explains this exact situation or close to it?
You could use Parse.com framework to retrieve data from a database. There is a lot of documentation on this.
In this link you can find a tutorial that will explain you how to load data from Parse and show it in your UITableView.
Storing Local (in-memory store):
For storing without a internet connection you could use Core Data Stack with NSInMemoryStoreType as storeType. This tutorial will give you a nice idea on how it works.
You can declare a model like it follows:
struct CoreDataModel {
let name: String
let bundle: NSBundle
init(name: String, bundle: NSBundle)
// other properties & methods
}
And then manage it with:
let model = CoreDataModel(name: "MyModel", bundle: myBundle)
let stack = CoreDataStack(model: model,
storeType: NSInMemoryStoreType,
concurrencyType: .MainQueueConcurrencyType)
// Use context
stack.managedObjectContext
I am in the process of transitioning over to Swift from Obj-C and I think I have a fairly good understanding of the ? ! concepts. I am however experiencing a bad access crash on a field that is nil.
I am using
var cell :ContactIInfoTableViewCell!
cell = tableView.dequeueReusableCellWithIdentifier("notes", forIndexPath: indexPath) as! ContactIInfoTableViewCell
if let clinic = receivedVisitDetails?.clinicNotes {
cell.textLabel?.text = clinic
}
Which produces the error if empty. My understanding was that the IF statement would stop this issue but it hasn't.
What am I doing wrong here?
UPDATE
This is a detail view for the core data fetch.
NSManagedObject is set as
var receivedVisitDetails: VisitDetails! = nil
The prepareForSeague on the previous view
let visits:VisitDetails = fetchedResultsController.objectAtIndexPath(indexPath!) as! VisitDetails
taskController.receivedVisitDetails = visits
The crash only happens when the clinicNotes is null.
After all edits and comments, the problem is in:
#NSManaged var clinicNotes: String
It's optional in your Core Data model, but not in your class. Should be changed to:
#NSManaged var clinicNotes: String?
Here's similar problem where Imanou suggests mogenerator, which can handle it for you. It automatically generates two classes for each managed object. Human part is suitable for editing (not touched by mogenerator when updating your model) and machine is not suitable for editing (rewritten every time you do update your model). Human part inherits from machine part.
Whenever I'm working with Core Data I do use it. I strongly suggest it as well. You can also add it to build phase, so, it automatically update your machine classes when you're building your project.
When using this construction, you don't have to use ? as it is unwrapped for you.
try
if let clinic = receivedVisitDetails.clinicNotes {
cell.textLabel?.text = clinic
}
I had a project that was working fine. It had "Core Data" checked, and had the data model all set up. I only started adding a couple entities and properties tonight. When I try to run my app now, it won't even load. It just crashes on me.
Here's the error:
'NSInvalidArgumentException', reason: 'executeFetchRequest:error: A fetch request must have an entity.'
I'm really scared because I don't have a backup of this and if I can't get it working I don't know what I'll do. :)
Thanks in advance!
EDIT:
I got fed up with my data, so I just copied a new blank xcdatamodel to my project and I'm going to start fresh. Thanks for the help!
My issue is I didn't use the same name for Entity and Class. Trivial solution to fix it is by giving them the same name.
If you are using MagicalRecored with Swift:
Make sure you use #objc directive in the Swift NSManagedObject subclass to make the class accessible to Objective-C code from the MagicalRecord library
#objc(MyEntity)
class MyEntity: NSManagedObject {
#NSManaged var myAttribute: Int16
}
After searching all over for a solution, what fixed it for me was doing a Clean/Build in Xcode.
Product->Clean, Product->Build, then try running it.
It seemed as if my data got corrupted, so I deleted my data model and the database in the iPhone simulator, and started fresh.
I had the same error.
For me, it is because I have added a new Model Version, but I did not set it as "Current Version". Careless me! To fix, select the xcdatamodel, click Design > Data Model > Set Current Version. The xcdatamodel file will then have a green tick.
Hopes that helps.
Also, make sure that your .xcdatamodeld file is in the "Copy Bundle Resources" phase of your Build Phases.
Here's what fixed it for me:
As I was converting to Swift 3, Xcode was giving me an error when declaring a new NSFetchRequest, saying that it needed a type. After adding the type, I did what anyone else would have assumed; if the request is typed, why specify an entity name? So, I removed it.
It actually was my mistake.
Swift 2.2:
let request = NSFetchRequest(entityName: "MyEntity")
When I first converted to Swift 3:
let request = NSFetchRequest<MyEntity>()
That was giving me an error. I ended up with this:
let request = NSFetchRequest<MyEntity>(entityName: "MyEntity")
And everything works fine. Personally, I'm not sure why it needs to have an entity name specified, if you're typing the request. Maybe they'll update that at some point (I hope)
i found this solution in the apple develper forum and it was exactly my problem!
the solutions is that the context must be defined inside the struct App.
not in the environment parameter
import SwiftUI
#main
struct CoreDataDemoApp: App {
private let context = CoreDataStack.context.
var body: some Scene {
WindowGroup {
ContentView()
.environment(\.managedObjectContext, context)
}
}
}
Check if,
the entity is present in the xcdatamodel file.
entity name used are same.
If you are using Swift 3 and Core Data's new stack syntax:
var persistentContainer: NSPersistentContainer = {
let container = NSPersistentContainer(name: "MyAppModel")
container.loadPersistentStores(completionHandler: {
(storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
} else {
print(storeDescription)
}
})
return container
}()
Then you should be using this fetch syntax:
let request: NSFetchRequest<Client> = Client.fetchRequest()
I had this error on the first fetch after app launches when using different variations:
let request: NSFetchRequest<NSFetchRequestResult> = Client.fetchRequest()
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Client")
I did stumble across the same precise error upon taking my first steps into Core Data (and iOS 11 and Swift 4). I started off a book (sixth edition meant to target Swift 4 but presumably including some legacy stuff).
As suggested in the book my code was:
let fetchRequest = NSFetchRequest<ReminderData>()
let entity = ReminderData.entity()
fetchRequest.entity = entity
do {
let rows = try managedObjectContext.fetch(fetchRequest)
} catch {
fatalError("Unresolved error")
}
It turned out that all I got from ReminderData.entity() is nil. Not sure if I did something wrong when setting up the data model or ... Apple's docs say that NSManagedObject.entity() must not be overwritten?
Long story short, the Codegen file ReminderData+CoreDataProperties.swift did include the solution:
#nonobjc public class func fetchRequest() -> NSFetchRequest<ReminderData> {
return NSFetchRequest<ReminderData>(entityName: "ReminderDB")
}
which was all I had to use to end-up with a proper NSFetchRequest, no fiddling with the NSEntityDescription, problem gone!
let fetchRequest = NSFetchRequest<ReminderData>(entityName: "ReminderDB")
do {
let rows = try managedObjectContext.fetch(fetchRequest)
} catch {
fatalError("Unresolved error")
}
I built clean, and that didn't fix it. Then I deleted the app, and that didn't fix it. Then I built clean and deleted the app AT THE SAME TIME, and that fixed it.
Just add the same problem. I copied all my entities. Deleted the data model, recreated an empty one and pasted the entities back into the new data model. Solved my issue.
First I downloaded the app's data through the Organizer (to see what was happening) and noticed that it offered me to save it under a previous project name. This puzzled me. So I exited XCode 4.6.1, deleted the app (and its data) from my iPhone, and came back.
This time I got an error saying Cannot create an NSPersistentStoreCoordinator with a nil model. So I looked into the AppDelegate.m file and changed the URLForResource in the - (NSPersistentStoreCoordinator *) persistentStoreCoodinator method. It was set to the name of my app, and I changed it to 'Model' so as to match the name of my Model.xcdatamodeld.
It's working now.
This happened to me when I was fetching from the wrong database. My application has 3 sqlite databases, and of course 3 ManagedObjectContext instances. Well I was submitting the wrong ManagedObjectContext to a method asking it to query a table that didn't exist in the ManagedObjectContext I submitted. After using the correct ManagedObjectContext, all was good.
I think the original question/problem, and also the issue that most of these answers fixes (just in different ways) is just a real simple one:
Anytime you modify your core data (like adding an entity as you mention), you either have to delete all existing data (if you haven't published your app yet), or add a new version to your model.
Just thought I would post this answer, even though this is an older question, because this answer seems pretty obvious and so far hasn't been discussed in any of the questions or comments I read above.
You can also use setter method from CoraData ... Just do something like this...
On your CustomCoreDataManager.m
import "ObjectiveRecord.h"
call init method like this
(instancetype)init {
self = [super init];
if (self) {
[[CoreDataManager sharedManager] setModelName:#"YourModelName"];
}
return self; }
Hope this helps to someone...
Maybe you are trying to load a Database from a different/the wrong bundle?
For instance from or within a Framework?
I had this issue and solved it by loading the DB from the bundle of the related Framework. And then it all worked fine!!
Swift 4 + MagicalRecord:
let frameworkBundle = Bundle(for: AClassFromTheFramework.self)
let managedObjectModel = NSManagedObjectModel.mergedModel(from: [frameworkBundle])
MagicalRecord.setShouldAutoCreateManagedObjectModel(false)
NSManagedObjectModel.mr_setDefaultManagedObjectModel(managedObjectModel)
MagicalRecord.setupCoreDataStack(withAutoMigratingSqliteStoreNamed: "db.sqlite")
And voila !
I faced same issue, actually i was calling MyEnty instead of MyEntity so please re-check what names you have given to your entities and call the same and also check whether you are calling same attributes that you have defined like name
In my case, it was because this dropdown was not set to "Current Product Module" in the Data Model Inspector in Xcode (13.4.1):
Once I set that, it stopped crashing.
Hope this helps!