Core Data batch size

Question

I'm new to Core Data. I'm working against a large database, so batching/faulting mechanism is important to me.

I understand how this works when using an NSFetchedResultsController paired with a UITableView, but what if I'm not using this pairing, i.e. what if I'm allowing users to navigate sequentially through a detail view controller (similar to how Apple's Mail program does it at the message level)?

Right now, I load the sorted fetch results into an NSArray and can traverse that as needed. But if I limit the batch size to 20 for the fetched results, what do I do when the user wants to navigate to object # 21?

Answer 1

While NSFetchedResultsController is designed to be used with a UITableView, you can still use it stand alone.

When creating a fetch request, setLimit determines how many total objects are returned. setBatchSize determines how many of those objects are un-faulted at a time. So, initially, all but the first 20 objects retrieved will be returned as faults. When you access item 21, it will fetch (un-fault) another 20 objects in the results set.

Answer 2

You use the fetchOffSet method to have the fetch request start the next batch fetch after the point you've already fetched.