NSPersistentStoreCoordinator with two types of persistent stores?

Question

In an iOS app, I would like to use an NSPersistentStoreCoordinator with both an NSIncrementalStore subclass, for fetching data from a REST API, but also with an SQLite store, to save to disk. If I add both types of persistent stores to my coordinator, however, calling save: on my managed object context has no effect. If I only add the one persistent store, not of the type for my NSIcrementalStore subclass, then the save works as intended.

Is there any way to achieve this functionality?

Answer 1

The best solution in my experience is to have multiple managed object contexts, each having its own model.

However, there is a way to accomplish what you want:

// create the store coordinator
NSPersistentStoreCoordinator *storeCoordinator = [[NSPersistentStoreCoordinator alloc] init];
// create the first store
NSPersistentStore *firstStore = [storeCoordinator addPersistentStoreWithType: NSIncrementalStore configuration:nil URL:urlToFirstStore options:optionsForFirstStore error:&error];
// now create the second one
NSPersistentStore *secondStore = [storeCoordinator addPersistentStoreWithType:NSSQLiteStore configuration:nil URL:urlToSecondStore options:optionsForSecondStore error:&error];

// Now you have two stores and one context
NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
[context setPersistentStoreCoordinator:storeCoordinator];

// and you can assign your entities to different stores like this
NSManagedObject *someObject = [[NSManagedObject alloc] initWithEntity:someEntity insertIntoManagedObjectContext:context];
// here the relevant part
[context assignObject:someObject toPersistentStore:firstStore]; // or secondStore ..

You should also check these links to get a better idea about how Core Data works:

Core Data Programming Guide - Persistent Store Coordinator

SO: Two persistent stores for one managed object context - possible?

SO: Can two managed object context share one single persistent store coordinator?

Also check the comment by TechZen in the second link about configurations and read about it in here:

Core Data Programming Guide - Configurations

and here is a nice tutorial to manage two object contexts:

Multiple Managed Object Contexts with Core Data