Core Data in Objective-C, 3rd Edition

Running with Scissors

Both of these APIs work by making changes directly on disk. When we use either of these APIs, Core Data will construct the appropriate SQL calls and then pass them to SQLite. Nothing gets loaded into memory and therefore the API is executed very quickly—just slightly slower than SQLite itself.

If we can just make changes and/or deletes on disk and avoid having to load them all into memory, why don’t we just do that all the time?

This API comes at a fairly significant cost. The changes that we make on disk aren’t passed to the NSManagedObjectContext instances in our application.

This means that we can very easily make a change to the data on disk and then our NSManagedObjectContext will try to make a different change and ...