Question

I’m curious. Apple says in the docs:

Core Data automatically fires faults
when necessary (when a persistent
property of a fault is accessed).
However, firing faults individually
can be inefficient, and there are
better strategies for getting data
from the persistent store (see “Batch
Faulting and Pre-fetching with the
SQLite Store”).

NSFetchRequest has this feature:

[fetchRequest setFetchBatchSize:20];

Is this essentially performing such a batch faulting like recommended?

Just to make this clear for others, faulting does not mean “turning into a fault” but it means “materializing it”, just like “making a Scooby-Doo out of it”. Pretty ugly wording error, in my opinion, but it’s at least consistent in the docs 😉

Answer 1

The documentation answers that question, IMO:

If you set a non-zero batch size, the
collection of objects returned when
the fetch is executed is broken into
batches. When the fetch is executed,
the entire request is evaluated and
the identities of all matching objects
recorded, but no more than batchSize
objects’ data will be fetched from the
persistent store at a time. The array
returned from executing the request
will be a proxy object that
transparently faults batches on
demand. (In database terms, this is an
in-memory cursor.)

That, to me, says that it divides the fetched results into batches that get faulted when any member of the batch is accessed.