Core Data Persistence with AFNetworking, Done Right

AFIncrementalStore is an NSIncrementalStore subclass that uses AFNetworking to automatically request resources as properties and relationships are needed.

Weighing in at just a few hundred LOC, in a single {.h,.m} file pair, AFIncrementalStore is something you can get your head around. Integrating it into your project couldn't be easier--just swap out your NSPersistentStore for it. No monkey-patching, no extra properties on your models.

Incremental Store Persistence

AFIncrementalStore does not persist data directly. Instead, it manages a persistent store coordinator that can be configured to communicate with any number of persistent stores of your choice.

In the Twitter example, a SQLite persistent store is added, which works to persist tweets between launches, and return locally-cached results while the network request finishes:

NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Twitter.sqlite"];
NSDictionary *options = @{ NSInferMappingModelAutomaticallyOption : @(YES) };

NSError *error = nil;
if (![incrementalStore.backingPersistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:options error:&error]) {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}

If your data set is of a more fixed or ephemeral nature, you may want to use NSInMemoryStoreType.

Mapping Core Data to HTTP

The only thing you need to do is tell AFIncrementalStore how to map Core Data to an HTTP client. These methods are defined in the AFIncrementalStoreHTTPClient protocol:

Don't worry if this looks like a lot of work--if your web service is RESTful, AFRESTClient does a lot of the heavy lifting for you. If your target web service is SOAP, RPC, or kinda ad-hoc, you can easily use these protocol methods to get everything hooked up.

- (NSDictionary *)representationsForRelationshipsFromRepresentation:(NSDictionary *)representation
                                                           ofEntity:(NSEntityDescription *)entity
                                                       fromResponse:(NSHTTPURLResponse *)response;

- (NSString *)resourceIdentifierForRepresentation:(NSDictionary *)representation
                                         ofEntity:(NSEntityDescription *)entity;

- (NSDictionary *)attributesForRepresentation:(NSDictionary *)representation
                                         ofEntity:(NSEntityDescription *)entity
                                     fromResponse:(NSHTTPURLResponse *)response;

- (NSURLRequest *)requestForFetchRequest:(NSFetchRequest *)fetchRequest
                             withContext:(NSManagedObjectContext *)context;

- (NSURLRequest *)requestWithMethod:(NSString *)method
                pathForObjectWithID:(NSManagedObjectID *)objectID
                        withContext:(NSManagedObjectContext *)context;

- (NSURLRequest *)requestWithMethod:(NSString *)method
                pathForRelationship:(NSRelationshipDescription *)relationship
                    forObjectWithID:(NSManagedObjectID *)objectID
                        withContext:(NSManagedObjectContext *)context;

Getting Started

Check out the example projects that are included in the repository. They are somewhat simple demonstration of an app that uses Core Data with AFIncrementalStore to communicate with an API for faulted properties and relationships. Note that there are no explicit network requests being made in the app--it's all done automatically by Core Data.

Also, don't forget to pull down AFNetworking with git submodule update --init if you want to run the example.

Requirements

AFIncrementalStore requires Xcode 4.4 with either the iOS 5.0 or Mac OS 10.6 (64-bit with modern Cocoa runtime) SDK, as well as AFNetworking 0.9 or higher.

Installation

CocoaPods is the recommended way to add AFIncrementalStore to your project.

Here's an example podfile that installs AFIncrementalStore and its dependency, AFNetworking.

Podfile

platform :ios, '5.0'

pod 'AFIncrementalStore'

Note the specification of iOS 5.0 as the platform; leaving out the 5.0 will cause CocoaPods to fail with the following message:

[!] AFIncrementalStore is not compatible with iOS 4.3.

Credits

AFIncrementalStore was created by Mattt Thompson.

Contact

Follow AFNetworking on Twitter (@AFNetworking)

Creators

Mattt Thompson
@mattt

License

AFIncrementalStore and AFNetworking are available under the MIT license. See the LICENSE file for more info.