Core Data Persistence with AFNetworking, Done Right

This is still in early stages of development, so proceed with caution when using this in a production application. Any bug reports, feature requests, or general feedback at this point would be greatly appreciated.

A lot of us have been burned by Core Data + REST frameworks in the past.
I can promise you that this is unlike anything you've seen before.

AFIncrementalStore is an NSIncrementalStore subclass that uses AFNetworking to automatically request resources as properties and relationships are needed. I had noticed NSIncrementalStore in the iOS 5 docs a while ago, but it was this article that got me to realize how unbelievably cool it was.

Weighing in at just over 300 LOC, 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.

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:

- (id)representationOrArrayOfRepresentationsFromResponseObject:(id)responseObject;

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

- (NSDictionary *)propertyValuesForRepresentation:(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;

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.

Check out the example project included in the repository. It's a 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. Don't forget to pull down AFNetworking with git submodule init && git submodule update if you want to run the example.

AFIncrementalStore requires iOS 4.0 and above, or Mac OS 10.6 (64-bit with modern Cocoa runtime) and above, as well as AFNetworking 0.9 or higher.

This project is just getting started. Next up for AFIncrementalStore are the following:

• Full Documentation
• Additional example projects
• POST to server when creating new managed objects
• Automatic If-Modified-Since & If-Match headers based on last request of resources.
• Default transformations for fetch request offset / limit to pagination parameters
• Examples of other API adapters (e.g. RPC, SOAP, ad-hoc)

AFIncrementalStore was created by Mattt Thompson.

Follow AFNetworking on Twitter (@AFNetworking)

Mattt Thompson
@mattt

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