Question

For example. if I have a chat app that uses objects like: ChatRoom and ChatMessage. (both subclasses of NSManagedObject)
And throughout the app I need to: search chat rooms / add massages / create chat rooms and messages / and any other manipulate.
Is it ok if I do everything directly with core data? I mean every time I need to search a chat room or something like that, to do it with NSFetchRequest or NSFetchedResultsController.

Answer 1

You can access the data whenever you need, of course. On the other hand you should try to use caching mechanism as much as possible.

For example, if you are using your data in UITableView you should defintely go with NSFetchedResultsController as it was created explicitly for UITableViews. From the apple docs on NSFetchedResultsController:

It optionally monitors changes to objects in its associated managed object context, and reports changes in the results set to its delegate (see “The Controller’s Delegate”).
It optionally caches the results of its computation so that if the same data is subsequently re-displayed, the work does not have to be repeated (see “The Cache”).

Otherwise, if you need the data just temporarily, you can access them of course using NSFetchRequest each time they are needed or cache them in your business objects if they don’t change or you know their lifetime otherwise.