That is where custom mapping models come into play. EXAMPLE SCENARIO Let us assume we have a view controller that shows comments. Furthermore, the server delivering the data sends the creation date in a custom format that requires further processing.We released our app to the App Store, just to realize afterwards that it would have been more efficient to store the transformed timestamp in our entity instead of doing the transformation whenever we access this attribute.Custom migration is quite a powerful tool and you can perform all kinds of transformations, e.g., change relationships or merge entities.In this guide, only changes of the attribute’s type are discussed, but this might be a good starting point for other kinds of migrations, too.If you are using Core Data, need to change your database scheme but Core Data cannot infer the changes on its own.And you don’t want to dig into the Core Data Programming Guide, you have come to the right place.
(This guide refers to Xcode Version 4.5.2 (4G2008a) and i OS 1.
VERSIONED CORE DATA MODEL You can skip this section if you are already familiar with versioned Core Data models.