Question

we are using core data for our online catalog and its working fine and app available in app store now I need to upgrade the core date with some of fields and attributes. It migrated to new one but old data already stored in the app are completely vanished. I tried various ways to retain it using this code

    NSString *databaseFilePath = [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"App_iOS.sqlite"];

    NSFileManager *fileManager = [NSFileManager defaultManager];
    [fileManager removeItemAtPath:databaseFilePath error:NULL];

    NSURL *storeUrl = [NSURL fileURLWithPath: databaseFilePath];

    NSError *error = nil;
    if( ![[self persistentStoreCoordinator] addPersistentStoreWithType:NSSQLiteStoreType  configuration: nil URL:storeUrl options:nil error:&error])
    {
        [__managedObjectContext insertObjects];
    }
    else
    {
        [__managedObjectContext updatedObjects];
    } 

I am not get solution yet to retain the data in app. I searched in internet for this most of the face the same problem but I am not receive the good solution yet

Answer 1

I’ve now found out that this is quite simple – once you know where to look.#
In my AppDelegate I set-up the NSPersistentStoreCoordinator – and you need to add some options to this to tell it to handle auto-migrate:

    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:

    [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,

    [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

    NSError *error;
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: [self managedObjectModel]];

    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType        configuration:nil URL:storeUrl options:options error:&error]) {
          // Handle error
        NSLog(@"Problem with PersistentStoreCoordinator: %@",error);
    }

Then you need to do in xCode:

1.  Select your xcdatamodeld file
2.  Select the Editor Menu at the top - then choose Add Model Version
3.  Now your xcdatamodeld file have two (modelname.xcdatamodel & modelname2.xcdatamodel ) .
4.  Now modelname.xcdatamodel  have the green check mark implies it is current version, but we need to change the modelname2.xcdatamodel as a current version
5.  Select the xcdatamodeld file and then select the View Menu at the top - then Choose Utilities - then Choose the Show File Inspector is shown in right side of Xcode and then Select the Versioned Core Data Model - have Current(DropDownList) - select modelname2(the one you just made current version have green check mark).
6.  Now when you install this version onto a device that has the old model - it will automatically upgrade that model to the new model.

This seems great and as simple as I wanted – but I think you need to be careful during development as you change a model – otherwise you will have to create a new version for each change.

I think what I will do is that I will keep all of the changed files and then once I get ready to deploy my update I’ll delete all the in-between files and just deploy with the oldest and latest models.