Sync eases your every day job of parsing a JSON response and getting it into Core Data. It uses a convention over configuration paradigm to facilitate your workflow.

  • Handles operations in safe background threads
  • Thread safe saving, we handle retrieving and storing objects in the right threads
  • Diffing of changes, updated, inserted and deleted objects (which are automatically purged for you)
  • Auto-mapping of relationships (one-to-one, one-to-many and many-to-many)
  • Smart-updates, only updates your NSManagedObjects if the server values are different (useful when using NSFetchedResultsController delegates)
  • Uniquing, Core Data does this based on objectIDs, we use your remote key (such as id) for this

Table of Contents



  changes: [AnyObject]!,
  inEntityNamed: String!,
  dataStack: DATAStack!,
  completion: ((NSError!) -> Void)!)


+ (void)changes:(NSArray *)changes
  inEntityNamed:(NSString *)entityName
      dataStack:(DATAStack *)dataStack
     completion:(void (^)(NSError *error))completion
  • changes: JSON response
  • entityName: Core Data’s Model Entity Name (such as User, Note, Task)
  • dataStack: Your DATAStack





    "id": 6,
    "name": "Shawn Merrill",
    "email": "",
    "created_at": "2014-02-14T04:30:10+00:00",
    "updated_at": "2014-02-17T10:01:12+00:00",
    "notes": [
        "id": 0,
        "text": "Shawn Merril's diary, episode 1",
        "created_at": "2014-03-11T19:11:00+00:00",
        "updated_at": "2014-04-18T22:01:00+00:00"


[Sync changes:JSON
       // New objects have been inserted
       // Existing objects have been updated
       // And not found objects have been deleted

Alternatively if you only want to sync users that have been created in the last 24 hours, you could do this by using a NSPredicate.

NSDate *now = [NSDate date];
NSDate *yesterday = [now dateByAddingTimeInterval:-24*60*60];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"createdAt > %@", yesterday];

[Sync changes:JSON

More Examples

Getting Started


Sync is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'Sync'


Core Data Stack

Replace your Core Data stack with an instance of DATAStack.

self.dataStack = [[DATAStack alloc] initWithModelName:@"Demo"];

Then add this to your App Delegate so everything gets persisted when you quit the app.

- (void)applicationWillTerminate:(UIApplication *)application {
    [self.dataStack persistWithCompletion:nil];

Primary key

Sync requires your entities to have a primary key, this is important for diffing otherwise Sync doesn’t know how to differentiate between entries.

By default Sync uses id from the JSON and remoteID from Core Data as the primary key. You can mark any attribute as primary key by adding hyper.isPrimaryKey and the value YES.

For example in our Designer News project we have a Comment entity that uses body as the primary key.

Custom primary key

Attribute Mapping

Your attributes should match their JSON counterparts in camelCase notation instead of snake_case. For example first_name in the JSON maps to firstName in Core Data and address in the JSON maps to address in Core Data.

There are two exceptions to this rule:

  • ids should match remoteID
  • Reserved attributes should be prefixed with the entityName (type becomes userType, description becomes userDescription and so on). In the JSON they don't need to change, you can keep type and description for example. A full list of reserved attributes can be found here

If you want to map your Core Data attribute with a JSON attribute that has different naming, you can do by adding hyper.remoteKey in the user info box with the value you want to map.

Custom remote key


You are free to use any networking library.

Supported iOS Versions

iOS 7 or above


Sync wouldn’t be possible without the help of this fully tested components:

  • DATAStack: Core Data stack and thread safe saving

  • DATAFilter: Helps you purge deleted objects, internally we use it to diff inserts, updates and deletes. Also it’s used for uniquing Core Data does this based on objectIDs, DATAFilter uses your remote keys (such as id) for this

  • NSManagedObject-HYPPropertyMapper: Maps JSON fields with their Core Data counterparts, it does most of it’s job using the paradigm “convention over configuration


Hyper made this. We’re a digital communications agency with a passion for good code and delightful user experiences. If you’re using this library we probably want to hire you.


Sync is available under the MIT license. See the LICENSE file for more info.