Question

I’m going through the Apress book Pro Core Data and it says the following:

…local caching of remote data can benefit from in-memory persistent
stores.

I fail to see how caching the data in an in-memory persistent store is any more useful than simply having your app’s root view controller hang on to the data. Can someone elaborate more fully on the kinds of situations where an in-memory persistent store might be useful?

Answer 1

Your question indicates a misunderstanding of MVC. You’ve asked “why would it be faster for the model to cache data rather than a controller.” Controller don’t hold data at all, so it doesn’t matter how fast it would or wouldn’t be. The model holds data. And in a Core Data app, the model is tied to a persistent store.

The fact that persistent stores can be in memory makes coding extremely convenient, since callers don’t have to worry about how the data is stored. In your example, callers would need to behave differently (deal with different classes) for data stored in a local store versus a remote store. Core Data abstracts that away, making it easy to move your store wherever you want it.