BNR Core Data Stack

Carthage compatible CocoaPods Compatible GitHub license Build Status

The BNR Core Data Stack is a small framework, written in Swift, that makes it easy to quickly set up a multi-threading ready Core Data stack.

For more details on the design methodology see: Introducing the Big Nerd Ranch Core Data Stack

For complete source documentation see: Documentation


With the introduction of Apple’s NSPersistentContainer, in iOS 10/macOS 10.12, BNR has chosen to deprecate the CoreDataStack class. See container example for tips on using an NSPersistentContainer

Apple has also added a type method entity() to NSManagedObject allowing us to deprecate CoreDataModelable and migrate many of those same convenience functions to an extension of NSManagedObject.

While Apple also introduced some type safety to their NSFetchedResultsController, we believe our FetchedResultsController provides a better API by:

Similarly our EnittyMonitor still serves a niche not covered by built in CoreData objects. See Entity Monitor

Minimum Requirements


  • macOS 10.10
  • tvOS 9.0
  • iOS 8.0

Build Time:

  • Xcode 8.0
  • Swift 3.0



Add the following to your Cartfile:

github "BigNerdRanch/CoreDataStack"

Then run carthage update.

Follow the current instructions in Carthage’s README for up to date installation instructions.


Add the following to your Podfile:

pod 'BNRCoreDataStack'

You will also need to make sure you’re opting into using frameworks:


Then run pod install.


Type Safe Monitors

Fetched Results Controller

FetchedResultsController<T> is a type safe wrapper around NSFetchedResultsController using Swift generics.


See BooksTableViewController.swift for an example.

Entity Monitor

EntityMonitor<T> is a class for monitoring inserts, deletes, and updates of a specific NSManagedObject subclass within an NSManagedObjectContext.


See EntityMonitorTests.swift for an example.

NSManagedObject Extensions

Adds convenience methods onNSManagedObject` subclasses. These methods make fetching, inserting, deleting, and change management easier.


let allBooks = try Book.allInContext(moc)
let anyBook = try Book.findFirstInContext(moc)
try Book.removeAllInContext(moc)

Constructing Your Stack

Import Framework

via: Carthage

import CoreDataStack

or via CocoaPods

import BNRCoreDataStack

Standard SQLite Backed

CoreDataStack.constructSQLiteStack(withModelName: "TestModel") { result in
    switch result {
    case .success(let stack):
        self.myCoreDataStack = stack
    case .failure(let error):

In-Memory Only

do {
    myCoreDataStack = try CoreDataStack.constructInMemoryStack(withModelName: "TestModel")
} catch {

Working with Managed Object Contexts

Private Persisting/Coordinator Connected Context

This is the root level context with a PrivateQueueConcurrencyType for asynchronous saving to the NSPersistentStore. Fetching, Inserting, Deleting or Updating managed objects should occur on a child of this context rather than directly.


Main Queue / UI Layer Context

This is our MainQueueConcurrencyType context with its parent being the private persisting context. This context should be used for any main queue or UI related tasks. Examples include setting up an NSFetchedResultsController, performing quick fetches, making UI related updates like a bookmark or favoriting an object. Performing a save() call on this context will automatically trigger a save on its parent via NSNotification.


Creating a Worker Context

Calling newChildContext() will vend us a PrivateQueueConcurrencyType child context of the main queue context. Useful for any longer running task, such as inserting or updating data from a web service. Calling save() on this managed object context will automatically trigger a save on its parent context via NSNotification.

let workerContext = myCoreDataStack.newChildContext()
workerContext.performBlock() {
    // fetch data from web-service
    // update local data

Large Import Operation Context

In most cases, offloading your longer running work to a background worker context will be sufficient in alleviating performance woes. If you find yourself inserting or updating thousands of objects then perhaps opting for a stand alone managed object context with a discrete persistent store like so would be the best option:

myCoreDataStack.newBatchOperationContext() { result in
    switch result {
    case .success(let batchContext):
        // my big import operation
    case .failure(let error):

Resetting The Stack

At times it can be necessary to completely reset your Core Data store and remove the file from disk, for example when a user logs out of your application. An instance of CoreDataStack can be reset by using the function resetStore(resetCallback: CoreDataStackStoreResetCallback).

myCoreDataStack.resetStore() { result in
    switch result {
    case .success:
        // proceed with fresh Core Data Stack
    case .failure(let error):


Please see our guide to contributing to the CoreDataStack

Debugging Tips

To validate that you are honoring all of the threading rules it’s common to add the following to a project scheme under Run > Arguments > Arguments Passed On Launch. 1

This will throw an exception if you happen to break a threading rule. For more on setting up Launch Arguments check out this article by NSHipster.

iCloud and iTunes Backup Considerations

By default the CoreData store URL can be included in the backup of a device to both iCloud and local disk backups via iTunes. For sensitive information such as health records or other personally identifiable information, you should supply a URL to the constructor that has been flagged as excluded from backup.


// Setup your URL
let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
var storeFileURL = URL(string: "MyModel.sqlite", relativeTo: documentsDirectory)!
do {
    var resources = URLResourceValues()
    resources.isExcludedFromBackup = true
    try storeFileURL.setResourceValues(resources)
} catch {
    //handle error ...

// Create your stack
CoreDataStack.constructSQLiteStack(withModelName: "MyModel", withStoreURL: storeFileURL) { result in
    switch result {
    case .success(let stack):
        // Use your new stack
    case .failure(let error):
        //handle error ...


Big Nerd Ranch

  • We Develop custom apps for clients around the world.
  • We Teach immersive development bootcamps.
  • We Write best-selling Big Nerd Ranch Guides.