MagicalRecord: multiple databases

Question

I have an app that uses MagicalRecord, and I'm pre-populating the database with a large amount of data that is used for reference. Within that same data model, I have user-definable information pertaining to things the user may do in the app.

The app was rejected because the pre-populated data is supposed to be marked as "do not backup". So, I'd like to have that data in a separate datastore so that I can keep the user data as backupable.

Is there a way to have two separate datastores using MagicalRecord?

Answer 1

I think it's possible, but not too easy though. As you know, to work with more than one database, you should bring some changes to your PersistentStoreCoordinator, so it will have two PersistentStores. After this, you Core Data stack would look like this:

The other way is two make two separate PersistentStoreCoordinators, each carrying one store.

In Magical Record, there are several class methods for adding stores in NSPersistentStoreCoordinator+MagicalRecord.h.

• (NSPersistentStore *) MR_addInMemoryStore;
• (NSPersistentStore *) MR_addAutoMigratingSqliteStoreNamed:(NSString *) storeFileName;
• (NSPersistentStore *) MR_addSqliteStoreNamed:(id)storeFileName withOptions:(__autoreleasing NSDictionary *)options;

I think, that this is the place where you could do the thing you want.

Also i should mention, that the whole proccess of setting up the stack goes in MagicalRecord+Setup.h

+ (void) setupCoreDataStackWithStoreNamed:(NSString *)storeName

So you can add your Stores and Coordinators there. I've never managed it by myself, that was just a brief investigation of a possible solution.

Answer 2

I was able to solve this issue using configurations. Since Magical Record always sends null for the configuration parameter, I broke apart setupCoreDataStackWithAutoMigratingSqliteStoreNamed and replaced it with a method that supports multiple configurations.

Because Magical Record does a good job of handling auto migrations, I first call setupCoreDataStackWithAutoMigratingSqliteStoreNamed, followed by cleanup, and then I supply my replacement code.

I have one object model with my seed data objects assigned the the "Seed" configuration and user objects assigned to the "User" configuration. Magical Record has already been initialized so it could auto migrate if necessary.

+(void) RB_setupMultipleStores:(NSString *) seedStoreName userStore:(NSString *) userStoreName
/* change persistent store to one with multiple configurations. Assumes Magical Record is initialized. */
{
NSError * error= nil;

[MagicalRecord cleanUp];

NSManagedObjectModel * model = [NSManagedObjectModel MR_defaultManagedObjectModel];

NSURL *seedURL = [NSPersistentStore MR_urlForStoreName:[seedStoreName stringByAppendingString:@".sqlite"]];

NSPersistentStoreCoordinator * coordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:model];

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                         [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                         [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption,
                         nil];

NSPersistentStore * seedStore =[coordinator
                                  addPersistentStoreWithType:NSSQLiteStoreType
                                  configuration:@"Seed"
                                  URL:seedURL
                                  options:options
                                  error:&error];
if (!seedStore || error)
{
    NSLog(@"Error setting up seed store:%@ for %@", [error localizedDescription], seedURL);
    exit(-1);
}

NSURL *userURL = [NSPersistentStore MR_urlForStoreName:[userStoreName stringByAppendingString:@".sqlite"]];

NSPersistentStore * userStore = [coordinator
                                 addPersistentStoreWithType:NSSQLiteStoreType
                                 configuration:@"User"
                                 URL:userURL
                                 options:options
                                 error:&error];

if (!userStore || error)
{
    NSLog(@"Error setting up user store:%@ for %@", [error localizedDescription], userURL);
    exit (-1);
}
[NSPersistentStoreCoordinator MR_setDefaultStoreCoordinator:coordinator];

[NSManagedObjectContext MR_initializeDefaultContextWithCoordinator:coordinator];
}

Also, MR 3.0 has concurrent stacks which may solve the problem once it is done.