Programming iOS 6, 3rd Edition

Core Data

The Core Data framework provides a generalized way of expressing objects and properties that form a relational graph; moreover, it has built-in facilities for persisting those objects to disk — typically using SQLite as a storage format — and reading them from disk only when they are needed, thus making efficient use of memory. For example, a person might have not only multiple addresses but also multiple friends who are also persons; expressing persons and addresses as explicit object types, working out how to link them and how to translate between objects in memory and data in storage, and tracking the effects of changes, such as when a person is deleted from the data, can be tedious. Core Data can help.

It is important to stress, however, that Core Data is not a beginner-level technology. It is difficult to use and extremely difficult to debug. It expresses itself in a highly verbose, rigid, arcane way. It has its own elaborate way of doing things — everything you already know about how to create, access, alter, or delete an object within an object collection becomes completely irrelevant! — and trying to bend it to your particular needs can be tricky and can have unintended side-effects. Nor should Core Data be seen as a substitute for a true relational database.

Therefore, I have no intention of explaining Core Data; that would require an entire book. Indeed, such books exist, and if Core Data interests you, you should read some of them. See also the Core Data Programming ...