I find myself struggling with Core Data quite a lot lately. In one of the WWDC talks, the Apple engineer talks about an easy way to easily debug Core Data activity.

To enable this, open your XCode project, go to Product, Scheme, Edit scheme. Click the arguments tab and add the following two arguments:

„-com.apple.CoreData.SQLDebug” and „1” (or „2” or „3”, higher numbers will yield more verbose output)

More details can be found here: http://stackoverflow.com/a/5289253/664449 (the answer also specifies why you need to use two arguments)

Official documentation: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/Articles/cdTroubleshooting.html#//apple_ref/doc/uid/TP40002320-SW21