How to resolve: "NSPersistentStoreCoordinator has no persistent stores"?

Question

I'm following this tutorial exactly, which adds CoreData to an existing app: https://www.youtube.com/watch?v=WcQkBYu86h8

When I get to the seedPerson() moc.save(), the app crashes with this error:

CoreData: error: Illegal attempt to save to a file that was never opened. "This NSPersistentStoreCoordinator has no persistent stores (unknown). It cannot perform a save operation.". No last error recorded.

The NSManagedSubclass has been added.

The DataController is wired up and I can step into it. It isn't until the save() that things go wrong. Any idea what I might have left out to cause this error?

Answer 1

Unfortunately, that video uses some code from Apple's website, and that code example is flawed. The main flaw is that it caches the MOC before the persistent store has been added to the MOC. Thus, if the creation of the store fails at all, the managed object context will be initialized with a persistent store coordinator that has no store.

You need use the debugger and step through the code that creates the PSC (the DataController.init method) and see why the failure happens. If you cut/paste the same way as in that example, then maybe you also forgot to change the name of your model when instantiating the model.

In any event, the most likely cause is that some initialization code in that function failed, and you are subsequently going happily along with a core data stack that has no stores.

Answer 2

I also followed that YouTube tutorial and had the same problem. I just removed the background thread block that adds the persistent store and it worked. Here's my DataController:

import UIKit
import CoreData

class WellbetDataController: NSObject {
    var managedObjectContext: NSManagedObjectContext

    override init() {
        // This resource is the same name as your xcdatamodeld contained in your project.
        guard let modelURL = NSBundle.mainBundle().URLForResource("DataModel", withExtension:"momd") else {
            fatalError("Error loading model from bundle")
        }

        // The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
        guard let mom = NSManagedObjectModel(contentsOfURL: modelURL) else {
            fatalError("Error initializing mom from: \(modelURL)")
        }

        let psc = NSPersistentStoreCoordinator(managedObjectModel: mom)
        self.managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
        self.managedObjectContext.persistentStoreCoordinator = psc

        let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
        let docURL = urls[urls.endIndex-1]
        /* The directory the application uses to store the Core Data store file.
        This code uses a file named "DataModel.sqlite" in the application's documents directory.
        */
        let storeURL = docURL.URLByAppendingPathComponent("DataModel.sqlite")
        do {
            try psc.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: storeURL, options: nil)
        } catch {
            fatalError("Error migrating store: \(error)")
        }



//        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) {
//            let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
//            let docURL = urls[urls.endIndex-1]
//            /* The directory the application uses to store the Core Data store file.
//            This code uses a file named "DataModel.sqlite" in the application's documents directory.
//            */
//            let storeURL = docURL.URLByAppendingPathComponent("DataModel.sqlite")
//            do {
//                try psc.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: storeURL, options: nil)
//            } catch {
//                fatalError("Error migrating store: \(error)")
//            }
//        }
    }
}