Restkit Core data integration with NSManagedObjectContext - iphone

Question

For the last weeks I am learning Restkit (v0.10.0) and core data and the possibilities are endless with these great tools. Problem is I am a bit overwhelmed on how to see the bigger picture here. And because of the very fast paced updating of Restkit most of the tutorials/demo code is out of date and not working properly any more.
I have managed to get my tableview filled with data from my json on a remote server. I also worked out on how to make the remote data leading in combination with caching working now, but I am struggling with the NSManagedObjectContext/NSEntityDescription (Core data) and how it works out with Restkit when using POST commands.
If I understand it correctly the record is created in Core Data (after the comment line // Create a new instance ) and after that that data is used to create a POST request so that the record is posted to the server.
This code is being used to create a new record on the server but when the code is executed (I see a record being created on my server) but my tableview is not updated accordingly, the table view is not updated and therefore the new record is first visible when restarting the app. Manually refreshing the data from the server does not help either.
Hopefully someone can give me some pointers, or maybe a tutorial with Restkit/core data and a POST combined. Thanks!
- (void)createGoalWithName:(NSString *)name andDescription:(NSString *)goalDescription
{
Goal* goal = [Goal object];
goal.identifier = 0;
goal.name = name;
goal.goalDescription = goalDescription;
// Create a new instance of the entity managed by the fetched results controller.
NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
[NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
[self saveContext];
[[RKObjectManager sharedManager].router routeClass:[Goal class] toResourcePath:#"/api/goals" forMethod:RKRequestMethodPOST];
[[RKObjectManager sharedManager] postObject:goal delegate:self];
[self.tableView reloadData];
}
- (void)saveContext {
NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
NSError *error = nil;
if (![context save:&error]) {
/*
Replace this implementation with code to handle the error appropriately.
abort() causes the application to generate a crash log and terminate.
You should not use this function in a shipping application,
although it may be useful during development.
If it is not possible to recover from the error,
display an alert panel that instructs the user to quit the application by pressing the Home button.
*/
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}

Answer 1

You have to use blocks when using RestKit+CoreData, and forget the router setup:
NSString *postUrl = #"/someurl/newelement";
[ [RKObjectManager sharedManager] loadObjectsAtResourcePath:postUrl usingBlock:^(RKObjectLoader* loader) {
loader.serializationMIMEType = RKMIMETypeJSON;
loader.delegate = nil;
loader.targetObject = nil;
loader.method= RKRequestMethodPOST; // change to GET, POST, PUT etc
}];

Answer 2

Since you don't include the UI code, it's hard to diagnose this problem fully, but one thing that might be happening since the updates are showing up when you restart the app, is that you're not properly synchronizing changes between the various thread's local managed object contexts. RestKit has its own managed object context since it doesn't run on the main UI thread.
The concept of working with multiple threads in Core Data is covered in this Apple document: http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/CoreData/Articles/cdConcurrency.html but the gist of it is that you need to register for the notification NSManagedObjectContextDidSaveNotification and then invoke mergeChangesFromContextDidSaveNotification: on the UI thread's managed object context to safely merge the changes done on the RestKit thread.
Keep in mind that the notification will be posted on the RestKit thread, so you probably have to run the update on the main UI thread, e.g. something like this in the method receiving the notification:
[self.managedObjectContextForMainThread performSelectorOnMainThread:#selector(mergeChangesFromContextDidSaveNotification:) withObject:notification waitUntilDone:YES];
Where the property NSManagedObjectContext* managedObjectContextForMainThread has been properly initialized to point to the UI thread's managed object context.
Hope this helps (if you haven't abandoned RestKit altogether...)

Answer 3

I'm still using a slightly older version of Restkit. But one key element is that a primary key attribute must be defined.
So that Restkit can keep your local stored objects and server objects in sync.
In your case, when defining mappings for your Goal object, you would do it like so:
goalMapping.primaryKeyAttribute = #"identifier";