iOS Programming: The Big Nerd Ranch Guide

Faults

Relationships are fetched in a lazy manner. When you fetch a managed object with relationships, the objects at the other end of those relationships are not fetched. Instead, Core Data uses faults. Faults are lightweight placeholder objects that provide an endpoint for a relationship until the potentially larger objects are actually needed. This provides both performance and memory usage boons to object management.

There are to-many faults (which stand in for sets) and to-one faults (which stand in for managed objects). So, for example, when the instances of BNRItem are fetched into your application, the instances of BNRAssetType are not. Instead, fault objects are created that stand in for the BNRAssetType objects until they ...