Can anyone give me some reference for this method "refreshAllObjects" in NSManagedObjectContext

[managedObjectContext refreshAllObjects]

Actually I am getting random error sometime during save context and when I call [managedObjectContext refreshAllObjects] after error, it allows me to save.
Could anyone please guide me about this method.

Calling refreshAllObjects calls refreshObject:mergeChanges on all objects in the context. You can see the documentation on refreshObject:mergeChanges here:

https://developer.apple.com/library/ios/documentation/Cocoa/Reference/CoreDataFramework/Classes/NSManagedObjectContext_Class/#//apple_ref/occ/instm/NSManagedObjectContext/refreshObject:mergeChanges:

It is possible that your persistent store has been modified by some other context, so you get an error when you try to save to it from your current context. If you refresh your current context first, then any modified data will be merged, and you can now save without conflicts.