Hard CoreData + iCloud scenario - core-data

Question

i'm having a very hard issue to solve. I've got this scenario:
My app uses CoreData to storing objects, I want to implement iCloud sync between devices... and my app requires an initial populated database.
The first time I launch my app, it's going to populate my database on the cloud and marks to YES some db'fields as "databaseInstalled". These fields are synced in the cloud too.
Now when another device launch the app for the first time, I was hoping to retrieve the field "databaseInstalled" to check whether inject or not some data but it's wrong...
If databaseInstalled is false, we inject data, if databaseInstalled it's true, we wait for iCloud sync.
The problem is that I retrieve the persistentStoreCoordinator asynchronically because of I don't want to block the app that is waiting to download data from iCloud...
So how can I know a priori if i need to populate the database or it has been filled on another device and I've just to download from iCloud the populated one?
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
if((__persistentStoreCoordinator != nil)) {
return __persistentStoreCoordinator;
}
__persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: [self managedObjectModel]];
NSPersistentStoreCoordinator *psc = __persistentStoreCoordinator;
// Set up iCloud in another thread:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// ** Note: if you adapt this code for your own use, you MUST change this variable:
NSString *iCloudEnabledAppID = #"this is a secret!";
// ** Note: if you adapt this code for your own use, you should change this variable:
NSString *dataFileName = #"you do not have to know.sqlite";
// ** Note: For basic usage you shouldn't need to change anything else
NSString *iCloudDataDirectoryName = #"Data.nosync";
NSString *iCloudLogsDirectoryName = #"Logs";
NSFileManager *fileManager = [NSFileManager defaultManager];
NSURL *localStore = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:dataFileName];
NSURL *iCloud = [fileManager URLForUbiquityContainerIdentifier:nil];
if (iCloud) {
NSLog(#"iCloud is working");
NSURL *iCloudLogsPath = [NSURL fileURLWithPath:[[iCloud path] stringByAppendingPathComponent:iCloudLogsDirectoryName]];
NSLog(#"iCloudEnabledAppID = %#",iCloudEnabledAppID);
NSLog(#"dataFileName = %#", dataFileName);
NSLog(#"iCloudDataDirectoryName = %#", iCloudDataDirectoryName);
NSLog(#"iCloudLogsDirectoryName = %#", iCloudLogsDirectoryName);
NSLog(#"iCloud = %#", iCloud);
NSLog(#"iCloudLogsPath = %#", iCloudLogsPath);
// da rimuovere
//[fileManager removeItemAtURL:iCloudLogsPath error:nil];
#warning to remove
if([fileManager fileExistsAtPath:[[iCloud path] stringByAppendingPathComponent:iCloudDataDirectoryName]] == NO) {
NSError *fileSystemError;
[fileManager createDirectoryAtPath:[[iCloud path] stringByAppendingPathComponent:iCloudDataDirectoryName]
withIntermediateDirectories:YES
attributes:nil
error:&fileSystemError];
if(fileSystemError != nil) {
NSLog(#"Error creating database directory %#", fileSystemError);
}
}
NSString *iCloudData = [[[iCloud path]
stringByAppendingPathComponent:iCloudDataDirectoryName]
stringByAppendingPathComponent:dataFileName];
//[fileManager removeItemAtPath:iCloudData error:nil];
#warning to remove
NSLog(#"iCloudData = %#", iCloudData);
NSMutableDictionary *options = [NSMutableDictionary dictionary];
[options setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption];
[options setObject:[NSNumber numberWithBool:YES] forKey:NSInferMappingModelAutomaticallyOption];
[options setObject:iCloudEnabledAppID forKey:NSPersistentStoreUbiquitousContentNameKey];
[options setObject:iCloudLogsPath forKey:NSPersistentStoreUbiquitousContentURLKey];
[psc lock];
[psc addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil
URL:[NSURL fileURLWithPath:iCloudData]
options:options
error:nil];
[psc unlock];
}
else {
NSLog(#"iCloud is NOT working - using a local store");
NSLog(#"Local store: %#", localStore.path);
NSMutableDictionary *options = [NSMutableDictionary dictionary];
[options setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption];
[options setObject:[NSNumber numberWithBool:YES] forKey:NSInferMappingModelAutomaticallyOption];
[psc lock];
[psc addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil
URL:localStore
options:options
error:nil];
[psc unlock];
}
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(#"iCloud routine completed.");
Setup *install = [[Setup alloc] init];
if([install shouldMigrate]) {
HUD = [[MBProgressHUD alloc] initWithView:self.window.rootViewController.view];
HUD.delegate = self;
HUD.labelText = NSLocalizedString(#"Sincronizzazione del database", nil);
[self.window.rootViewController.view addSubview:HUD];
[HUD showWhileExecuting:#selector(installDatabase) onTarget:install withObject:nil animated:YES];
}
else {
[[NSNotificationCenter defaultCenter] postNotificationName:#"setupCompleted" object:self];
}
//[[NSNotificationCenter defaultCenter] postNotificationName:#"icloudCompleted" object:self userInfo:nil];
[[NSNotificationCenter defaultCenter] postNotificationName:#"setupCompleted" object:self];
});
});
return __persistentStoreCoordinator;
}

Answer 1

You can't know whether or not there's going to be data available in iCloud until you finish syncing with iCloud. That means that you've got two options:
Make the user wait until the sync is done.
Start up with your default database and merge changes from iCloud when possible.
With iCloud, you need some strategy for resolving conflicts between local data and cloud data because you have to deal with the fact that users might change data on more than one device at the same time. Once you have that in place, it seems pretty clear that the second option above is the better one: users get to start using your app right away, and data from the cloud is merged when it's available.

Answer 2

I had exactly same problem.
Check out my question & my answer to it iCloud + CoreData - how to avoid pre-filled data duplication?
Actually it doesn't work 100% ok. If you dare to try it I can explain you how you might make it work 100% correctly (I haven't tried yet, though).
Taking into account that you have a lot of data to pre-populate my solution might now work out for you.

Answer 3

There is no way to determine whether a data store is being opened for the first time. At least not on iCloud Core Data store. Think of it, iCloud should also work off-line – that is, all changes should be buffered when the user is disconnected from the Internet and then uploaded when the connection is restored. There is no way to check whether a data store was initialized without potentially making the user wait for a few minutes (or even indefinitely if the device is off-line) to ask iCloud's copy of the data sore.
To solve this, you'll need to follow these four simple guidelines:
Have a way to de-duplicate pre-populated records.
Have a way to identify pre-populated records and differentiate it from user-entered ones.
Run the de-duplication process every time new transaction records came in from iCloud.
Only seed data records once per device/account combination.
You can read more details here: http://cutecoder.org/programming/seeding-icloud-core-data/