No NSEntityDescriptions in any model claim the NSManagedObject subclass

34
votes

I am new to CoreData 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?

8
iosswift
Did you misspell the name of your model when creating the persistent container? - Joakim Danielson
Double checked it, and I did not misspell it - dypbrg
Found the culprit!! When instantiating the fetchrequest, I should have used NSFetchRequest<Product>(entityName: "Product") instead of Product.fetchRequest() as! NSFetchRequest<Product>. - dypbrg
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. - Mark
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. - Victor Engel

8 Answers

36
votes

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.

Changing the module field

13
votes

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 {

}
9
votes

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.

6
votes

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)
        }
    }
}
5
votes

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.)

1
votes

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

let container = NSPersistentContainer(name: "DataModel")
0
votes

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 = {...}
0
votes

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)

Core Data