Core Data: Apple's API for Persisting Data on Mac OS X

Author: Marcus Zarra

http://www.pragprog.com/titles/mzcd/core-data

Core Data has some of the best built-in documentation out of all of the Cocoa frameworks, but this book is a great complement to that documentation.  Again, don't be turned off by the "Mac" in the title, as almost all of the elements of Core Data are identical between the Mac and iPhone, as of iPhone OS 3.0.

Where this book excels is in the practical matters of using Core Data.  His performance tuning chapter alone is worth the book's price, because it is a collection of best-practices from various talks by Apple engineers.  There is also a great chapter on iPhone-specific Core Data topics, such as dealing with NSFetchedResultsController.  You may want to read the Core Data chapter in iPhone SDK Development in parallel with this book, as both handle these concepts from slightly different perspectives.