Core data update model with app update? - iphone

Question

everyone who work with Core Data know the message "the model used to open the store is incompatible with the one used to create the store".
Then I have to delete my app from simulator, and rebuilding it again.
My question is if I submit an app v 1.0, then add some entities to core data in v 1.1, does this mean that the users of 1.0 who updated to 1.1 will have their data cleared up?

Answer 1

You will need to create a new model version for your model, and migrate the database. You can do a lightweight migration if your model changes are within the required changes. If not, you will need to tell core data how to migrate your data. Check the migration documentation: http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/CoreDataVersioning/Articles/Introduction.html

Answer 2

In your case it sounds like a simple extension to your old data model. If you just really add some new entities or even new classes then the so called leightweight migration is the right way to go for you.
Actually in this case you almost do not have anything to do, but create your second model IN ADDITION to your original model. It is important, that you have BOTH model, then the app will just load your 1st version without any problems as well as the new version.
Don't forget to mark your new model as the new one!
Try to be careful when creating the new model, since deleting a model is a real hassle.
Your code will look very similar to this:
-(NSManagedObjectContext *)managedObjectContext {
if (managedObjectContext != nil) {
return managedObjectContext;
}
NSPersistentStoreCoordinator *lC = [self persistentStoreCoordinator];
if (lC != nil) {
managedObjectContext =[[NSManagedObjectContext alloc] init];
[managedObjectContext setPersistentStoreCoordinator: lC];
}
return managedObjectContext;
}
- (NSPersistentStoreCoordinator *) persistentStoreCoordinator {
if (persistentStoreCoordinator != nil) {
return persistentStoreCoordinator;
}
persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: [self managedObjectModel]];
// Allow inferred migration from the original version of the application.
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
[NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];
NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: #"DBName.sqlite"]];
NSError *error = nil;
if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl
options:options error:&error]){
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
}
return persistentStoreCoordinator;
}
- (NSManagedObjectModel *) managedObjectModel {
if (managedObjectModel != nil) {
return managedObjectModel;
}
managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];
return managedObjectModel;
}