Question

This is my first project using RestKit and I am trying to make my simple iOS application synchronize with a set of API served by a Django application using the Tastypie package. My iOS application is based on the Core Data Default Xcode application.

I’m trying to retrieve objects from a simple model :

Car (name (string), public (boolean), id (integer), created (datetime))

My API looks like that for collections :

http://www.example.com/api/v1/car/?format=json

{"meta": {"limit": 20, "next": null, "offset": 0, "previous": null, "total_count": 1}, "objects": [{"created": "2012-07-04T13:47:37+00:00", "id": "1", "name": "BMW", "public": true, "resource_uri": "\/api\/v1\/car\/1\/",}]}

And for 1 object :

http://www.example.com/api/v1/car/1/?format=json

{"created": "2012-07-04T13:47:37+00:00", "id": "1", "name": "BMW", "public": true, "resource_uri": "\/api\/v1\/car\/1\/",}

Given this context, in my iOS application I have configured my store in my Application Delegate

-(void)configureObjectStore { 
// Initialize the RestKit Object Manager
RKObjectManager *objectManager = [RKObjectManager objectManagerWithBaseURL:[[NSURL alloc] initWithString:@"http://www.example.com/api/v1"]];
objectManager.client.requestQueue.showsNetworkActivityIndicatorWhenBusy = YES;

// Initialize object store
objectManager.objectStore = [RKManagedObjectStore objectStoreWithStoreFilename:@"database.sqlite"];

[self coreDataMapping];
}

And set my mapping inside by Application Delegate (not sure that this should be in here…)

- (void)coreDataMapping {
// Now for the object mappings
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Car" inManagedObjectContext:self.managedObjectContext];
RKManagedObjectMapping* carMapping = [RKManagedObjectMapping mappingForEntity:entity inManagedObjectStore:[RKObjectManager sharedManager].objectStore];
[carMapping mapKeyPath:@"id" toAttribute:@"carId"];
[carMapping mapAttributes:@"name", nil];
[carMapping mapKeyPath:@"public" toAttribute:@"public"];
[carMapping mapKeyPath:@"created" toAttribute:@"created"];
carMapping.primaryKeyAttribute = @"carId";

[[RKObjectManager sharedManager].mappingProvider addObjectMapping:carMapping];
}

Then in my main controller, where i want to load in a table view all of my objects (all of the cars)

- (void)loadData { 
// Load the object model via RestKit
RKObjectManager* objectManager = [RKObjectManager sharedManager];
[objectManager loadObjectsAtResourcePath:@"/car/1/?format=json" usingBlock:^(RKObjectLoader *loader) {
loader.objectMapping = [objectManager.mappingProvider objectMappingForClass:[Car class]];
loader.delegate = self;
}];
}

When i fire my app and try to load the objects list, it triggers the didFailWithError method from the delegate and i have the following stack :

I restkit.core_data:RKInMemoryManagedObjectCache.m:34 Creating thread-local entity cache for managed object context: <NSManagedObjectContext: 0x887f1b0>
I restkit.core_data:RKInMemoryManagedObjectCache.m:50 Caching instances of Entity 'Car' by primary key attribute 'carId'
E restkit.core_data:RKManagedObjectStore.m:262 Core Data Save Error
                                NSLocalizedDescription: (null)
                                NSValidationErrorKey: (null)
                                NSValidationErrorPredicate: (null)
                                NSValidationErrorObject: (null)
E restkit.core_data:RKManagedObjectLoader.m:167 Failed to save managed object context after mapping completed: The operation couldn’t be completed. (Cocoa error 134020.)
Hit error: Error Domain=NSCocoaErrorDomain Code=134020 "The operation couldn’t be completed. (Cocoa error 134020.)" UserInfo=0x89612c0 {NSAffectedObjectsErrorKey=<Car: 0x6c85670> (entity: Car; id: 0x6c65790 <x-coredata:///Car/t318CE65F-E4FE-44E1-813B-GEZG54> ; data: {
    created = "2012-07-04 13:47:37 +0000";
    favorites = (); (Note this relation is not mapped in the API but it is not required)
    carId = 1;
    modified = nil;
    name = BMW;
    public = 1;
}), NSUnderlyingException=Store <NSSQLCore: 0x88848c0> (URL: file://localhost/Users/me/Library/Application%20Support/Documents/database.sqlite) cannot hold instances of entity (<NSEntityDescription: 0x886f650>) name Car, managedObjectClassName Car, renamingIdentifier Car, isAbstract 0, superentity name (null), properties {
created = "(<NSAttributeDescription: 0x886dce0>), name created, isOptional 1, isTransient 0, entity Car, renamingIdentifier created, validation predicates (\n), warnings (\n), versionHashModifier (null)\n userInfo {\n}, attributeType 900 , attributeValueClassName NSDate, defaultValue (null)";
favorites = "(<NSRelationshipDescription: 0x886e900>), name favorites, isOptional 1, isTransient 0, entity Car, renamingIdentifier favorites, validation predicates (\n), warnings (\n), versionHashModifier (null)\n userInfo {\n}, destination entity Favorite, inverseRelationship list, minCount 0, maxCount 0, isOrdered 0, deleteRule 1";
carId = "(<NSAttributeDescription: 0x886dd80>), name carId, isOptional 1, isTransient 0, entity Car, renamingIdentifier carId, validation predicates (\n), warnings (\n), versionHashModifier (null)\n userInfo {\n}, attributeType 100 , attributeValueClassName NSNumber, defaultValue 0";
name = "(<NSAttributeDescription: 0x886de20>), name name, isOptional 1, isTransient 0, entity Car, renamingIdentifier name, validation predicates (\n), warnings (\n), versionHashModifier (null)\n userInfo {\n}, attributeType 700 , attributeValueClassName NSString, defaultValue (null)";
public = "(<NSAttributeDescription: 0x886de70>), name public, isOptional 1, isTransient 0, entity Car, renamingIdentifier public, validation predicates (\n), warnings (\n), versionHashModifier (null)\n userInfo {\n}, attributeType 800 , attributeValueClassName NSNumber, defaultValue (null)";
}, subentities (null), userInfo {
}, versionHashModifier (null)}

I have tried out many things but i have the feeling that i’m going round in circles here. Any advice will be warmly welcome.

Thank you for your time and support,
Regards,

PS : We should be able to rule out errors unrelated to RestKit since the application was working smoothly before the integration.

Answer 1

Since this question was left without answer, I’ll answer it myself with how I went forward with these issues.

I have actually abandoned RestKit which is certainly very powerful but I couldn’t bent it enough so it would work with Django-Tastypie instead I went to AFNetworking which is less high-level but allowed me to do my own API to Core Data backend and turned out quite convenient.

I hope this might help some other lost soul.
Regards,