What is Core Data Source Fetch

Question

I am looking at the Entity Mapping panel of core data in Xcode, and notice a setting named Source Fetch. There are two options Default and Custom. What is this Source Fetch about?

Answer 1

You specify the sourceExpression for the mapping using a combination of the the source fetch popup menu and the text view beneath it. You can select either the default fetch—in which case you can optionally specify a filter predicate for the fetch—or a custom fetch, in which case you specify the source expression directly.

Entity Mapping Detail