No NSEntityDescriptions in any model claim the NSManagedObject subclass

Question

I am new to Core Data and I'm trying to create a caching mechanism wherein after parsing objects from the API, I save them to the data model then fetch it again to show it on the tableview. I'm trying to fetch it using NSFetchedResultsController. Upon initialization of the NSFetchedResultsController, I'm encountering this runtime exception:

2018-12-09 15:03:20.493509+0800 [5184:148001] [error] error: 
No NSEntityDescriptions in any model claim the NSManagedObject subclass 
'Product' so +entity is confused.  Have you loaded your 
NSManagedObjectModel yet ?
CoreData: error: No NSEntityDescriptions in any model claim the 
NSManagedObject subclass 'Product' so +entity is confused.  Have you 
loaded your NSManagedObjectModel yet ?
2018-12-09 15:03:20.493718+0800[5184:148001] [error] error: + 
[Product entity] Failed to find a unique match for an 
NSEntityDescription to a managed object subclass
CoreData: error: +[Product entity] Failed to find a unique match for an 
NSEntityDescription to a managed object subclass

What could be the reason why?

Calton

Did you misspell the name of your model when creating the persistent container? – Geomorphic

Double checked it, and I did not misspell it – Calton

Found the culprit!! When instantiating the fetchrequest, I should have used NSFetchRequest<Product>(entityName: "Product") instead of Product.fetchRequest() as! NSFetchRequest<Product>. – Calton

tldr; initialise your NSManagedObjectContext. This was one of the few stackoverflow questions i came across while trying to debug my Coredata issue so I'll put my solution here. I had various methods/functions working till I began to delete/print not that this really matters. But the difference between the functions I was most recently working on was that the context was not initialised. I was calling my generic type E, with a fetchrequest before the context was assigned. So hope this helped someone. – Tesstessa

Another cause of this error can be if a new entity was created and it was set up differently from the other entities. I'm referring to the Module and Codegen fields in the Entity inspector. – Ionia

Answer 1

If you ever encounter an issue similar to this using SwiftUI, you can try changing the entity's class module from Global Namespace to Current Product Module.

Go to your xcdatamodeld file and select the problematic entity. Then in the data model inspector, change the Module field from the default Global namespace to available value "Current Product Module" by clicking on the arrow at the right of the field.

This allowed my app to compile without encountering the error.

Cheliform

I did that, but it didn't resolve my issue. How should the Codegen be defined? Would that matter? – Postcard

Answer 2

My experience:

The entity class was missing the @objc(Person) line above the class name. I do have more classes that are working without this line but only when creating this specific entity, I have got this error.

@objc(Person)
public class Person: NSManagedObject {

}

Sylvester

Thanks, but by adding this line, I got more new warning and errors...... – Parenthesis

Answer 3

I came across the same issue when I changed the Codegen property of a Core Data Model to the type Category/Extension, to create a custom class for the Core Data Model.

As pointed out by @dypbrg, changing the following code segment

Product.fetchRequest() 

to the following code segment

NSFetchRequest<Product>(entityName: "Product")

seems to solve the issue.

Halpin

why we cannot use Product.fetchRequest() ? – Dibbell

@MichałZiobro, they are different return types. Product.fetchRequest() returns the generic NSFetchRequest<NSFetchRequestResult>, while NSfetchRequest<Product>(entityName: "Product") returns NSFetchRequest<Product>. It appears to be an issue with force casting the former with as! NSFetchRequest<Product>. – Jonellejones

It's a sad state of affairs today being 2020 something – Bobbette

@Jonellejones But then you can do this let fetchRequest: NSFetchRequest< Product > = Product.fetchRequest() to be in proper type – Attraction

Answer 4

For anyone who has this problem with hybrid projects (Obj-C + Swift).

In my case, CoreData xcdatamodel is delivered as an asset inside SPM package and is used inside this package. With Swift projects there are no problems but with hybrid one I faced the same issue.

The solution that solved my problem:

1. use @objc annotation for NSManagedObjects as mentioned by @Sam

    @objc(Entity) 
    public class Entity: NSManagedObject {
   
    }
   

2. Use Global namespace instead of Current Product Module for each entity (check @Pomme2Poule's answer how to do that)

Estren

I'm having this problem with a .framework, but I don't need the 2 solutions, only one or the other is enough. Any idea why? – Bugbane

Answer 5

In my case I was using it SwiftUI the NSManagedObjectContext was being used before persistent store async function returned.

I then followed the core data sample project with Xcode to solve the issue:

@main
struct TestCoreDataApp: App {
    //Inside the PersistenceController initialiser the store is loaded, so gives it time before passing the context to the SwiftUI View
    let persistenceController = PersistenceController.shared

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environment(\.managedObjectContext, persistenceController.container.viewContext)
        }
    }
}

Manufactory

this was exactly my problem. I was trying to initialise the container and pass in the context in one step like this .environment(\.managedObjectContext, PersistenceController.shared.container.viewContext). I didn't realise that instantiating the controller in the struct would have such a big effect. – Azarcon

Yes, the standard core data Xcode template project provides a sample project which gives a clear idea as to how to use Core Data with SwiftUI. – Manufactory

@OliverD, if you are targeting the iOS 15 and above, now you can directly use it as you were using it. Refer developer.apple.com/wwdc21/10017 (18:16) – Manufactory

Answer 6

In my case, I had changed the name of an entity and the swift-class but had forgot to update to the new swift-class name in the xcdatamodeld.

(In xcdatamodel view, under "CONFIGURATIONS" in the left pane, select "Default" and make sure the name of the classes are correct.)

Apophysis

Answer 7

I've encounter same issue and finally locate the root cause at persistentContainer lazy initilaize.

In AppDelegate.swift, remove lazy works for me.

// MARK: - Core Data stack

    lazy var persistentContainer: NSPersistentCloudKitContainer = {...}

Minium

Answer 8

For me, I had not named the NSPersistentContainer in the AppDelegate the same as the xcdatamodelId I had created.

let container = NSPersistentContainer(name: "DataModel")

Erena

Answer 9

I want to add in my case this error occured after I had moved my xcdatamodeld and related files to another folder. Deleting and recreating data model file fixed it for me.

If this error occurs after you moved some files something probably was not moved correctly.

Celom

Answer 10

I have checked all above. My case is as simple as I wrote wrong DB(Container) name. Warning and related error disappeared when I put "Some" instead of "SomeApp".

It is (works):

        container = NSPersistentContainer(name: "Some")

It was (wrong):

        container = NSPersistentContainer(name: "SomeApp")

May be this will be of some help to anybody.

Kismet