'An NSManagedObject of class 'className' must have a valid NSEntityDescription.' error

In my case the same problem was in @objc modifier in auto-generated header of data-class

@objc(CachedMovie)
public class CachedMovie: NSManagedObject {

I just removed @objc(CachedMovie) and it began to work

In AppDelegate check persistent container name.

let container = NSPersistentContainer(name: "CoreData")

If you trying to reach nonexistent Core Data, that may manifest as this error.

Name should be exact same as .xcdatamodeld object in navigation menu.

If you are using coreData from a static library make sure you specify the module aswell

This gives you the correct entity access MyStaticLibrary.MyManagedObject

So if your receiving warnings with this dot notation, its not looking in your module

One way this could happen is by trying to rename your entities. Make sure that these are the same!

I've got the same issue. In my case I used CoreData initialised and managed in framework wich I integrated with main app via SPM.

Solution

First, in the framework provide module name for entity by hand, by following steps:

1. open .xcdatamodel,
2. select Entity which you want to edit,
3. open Data Model Inspector (the 4th panel in right sidebar),
4. at section Class element Module by default presents Current Product Module -- enter here your Module name

Repeat these steps for each entity.

Second, in the framework override description for each NSManagedObject you use in project, f.ex. you have:

public class Person: NSManagedObject {

}

override there description with String without module name, like:

public class Person: NSManagedObject {

    public override var description: String {
        return "Person"
    }
}

Code presented above will help if you use convenience initialiser for Person (like Person(context: Context)) which uses description to specify Person.entity().

For me, I forgot to add @objc(Reminder) in this below example. I wrote the NSManagedObject class programmatically.

@objc(Reminder)
public class Reminder: NSManagedObject {


}

I encountered this issue using Swift Package Manager to import a Swift Package that had a model file included as a resource. In my case setting the Module of my entity to Current Production Module produced an incorrect value in the model file. When I used the debugger to print the model after loading the persistent container the fully qualified class name was something like Module_Module.Class instead of the expected Module.Class. I had to manually type the module name instead of using Current Production Module to resolve the issue.

in your file modeldataClass probably name of Class is incorrect cause before you change name something in your name class

The mistake I made was to change the name of the entity and the generated "NSManagedObject Subclass" and not updating the name of the class. How to fix:

• open .xcdatamodeld
• click on the entity
• open the right panel
• Go to Data Model Inspector
• Change the name of the Class text field

I was trying out adding CoreData to existing project and I renamed things a lot. I ended up with multiple .xcdatamodeld without knowing it. The solution was removing .xcdatamodeld and generated NSManagerObject and recreating it again.

it easy to answer to this question. without removed

@objc(Workout)

the solution is on documentary Core Data Programming on "Entity Name and Class Name". here in your Xcode before doing (Editor -> Create NSManagedObject SubClass) must change your class Name of Entities to add "MO", CoreData can differentiate between class Name and Entitie Name. and the

@objc(Workout) 

will not be created, give us this one:

class CDWorkoutMO: NSManagedObject {

 class func createWorkout(workoutInfo : Workout, in context: NSManagedObjectContext) -> CDWorkoutMO {
    let workout = CDWorkoutMO(context: context)
    workout.name = "anyName"
    return workout
}
}

like I do on my Xcode

For SwiftUI you need to also update this method from SceneDelegate:

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    //This gets the context from AppDelegate and sets is as moc environment variable
    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    let contentView = ContentView().environment(\.managedObjectContext, context)
    //...
}

In my case, I had my Core Data model inside a Swift Package and had to follow this amazing guide and finally this is what did it:

I opened the model and selected the entity and in the right panel I selected the Data Model Inspector and in the Class panel, I manually entered the Module’s name i.e. the Swift Package name.