NSIncrementalStore to-one relationship fault fires immediately (eagerly loaded?)

Question

I noticed that the fault for a to-one relationship fires immediately when the fetch request is executed even though I'm not accessing the relationship. Particularly, a breakpoint in the method newValueForRelationship:forObjectWithID:withContext:error: is hit immediately in the NSIncrementalStore subclass.

- (id)newValueForRelationship:(NSRelationshipDescription *)relationship
          forObjectWithID:(NSManagedObjectID *)objectID
              withContext:(NSManagedObjectContext *)context
                    error:(NSError **)error

https://developer.apple.com/library/mac/documentation/CoreData/Reference/NSIncrementalStore_Class/index.html#//apple_ref/occ/instm/NSIncrementalStore/newValueForRelationship:forObjectWithID:withContext:error:

The breakpoint is only hit when I access the relationship as expected for to-many relationships as expected (lazy loaded).

Can someone please help?

Answer 1

This is all about designing your own NSIncrementalStore. Please go through doc Incremental Store Programming Guide.

Here are extracts from the guide:

If the backing data store makes to-one relationships readily available, your incremental store returns to-one relationships in newValuesForObjectWithID:withContext:error:. If your app and data store are more efficient when all relationship fetching is deferred, your store may instead return them in newValuesForRelationship:forObjectWithID:withContext:error:.