Save In-Memory store to a file on iOS

Question

Let's say I already setup a in-memory core data store using this:

- (NSPersistentStore *)addPersistentStoreWithType:(NSString *)storeType configuration:(NSString *)configuration URL:(NSURL *)storeURL options:(NSDictionary *)options error:(NSError **)error;

and saved a lot of things to it.

Now I want to save all of this store into a file.

Is that possible?

I tried many kind of search but it looked like no one has ever bumped into this issue before.

Answer 1

There's no way to just save the in-memory NSPersistentStore to a file. It doesn't conform to NSCoding or provide any methods of its own that would enable this, and the only way to ask it for its data is the usual Core Data approach of fetching it.

However, you can migrate to a file-based store pretty easily. Use your persistent store coordinator to migrate the memory-based store to a file. First make sure that you don't have any objects that still make use of the memory-resident store (NSManagedObjectContext, NSManagedObject). Then do something like:

NSURL *fileURL = // set this up to have the URL of the file you want
NSError *error = nil;
NSPersistentStore *fileStore = [self.persistentStoreCoordinator
    migratePersistentStore:self.memoryResidentStore
    toURL:fileURL
    options:nil
    withType:NSSQLiteStoreType
    error:&error];

Once you do this, the old persistent store (self.memoryResidentStore in the code above) is no longer useful.