NSPredicate to exclude NSManagedObjects that haven't been saved in an NSFetchedResultsController

Question

Building on this question, I've managed to use undo groups and a single managed object context to handle adding a Cocktail that can reference existing Ingredients and/or Brands.

Now I'm stuck with a UI nit -- in the fetched results controller (sorted by cocktail.name) you can briefly see an empty row for the to-be-added Cocktail. Marcus Zarra suggested:

You can add to the predicate to filter out unsaved objects, for example by using (entity.isTemporaryID == NO).

but every iteration I've tried comes back with errors of the form

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath entity.isTemporaryID not found in entity <NSSQLEntity Cocktail id=4>'

How can one execute the equivalent of [[cocktail objectID] isTemporaryID] in an NSPredicate?

Answer 1

The call is on the objectID not the managed object:

BOOL isTemporary = [[managedObject objectID] isTemporaryID];

See this section of the Core Data Programming guide for more details.

I'm not sure why you're seeing an empty row for an unadded entity. If the entity hasn't been added then it should be fetched by the fetched results controller. It sounds like you have inserted the entity into the context but have not yet populated it.

If that is the case, you can use a predicate to exclude entities that have some or all of their properties empty. If you end up doing this a lot, you might want to add a flag property to the class which will return NO (via a custom getter) if entity is not in a state to be displayed.

Answer 2

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath entity.isTemporaryID not found in entity <NSSQLEntity Cocktail id=4>'

How can one execute the equivalent of [[cocktail objectID] isTemporaryID] in an NSPredicate?

Do that.

What you asked for is not [[cocktail objectID] isTemporaryID], it's [[cocktail entity] isTemporaryID]. If you want objectID (which you do, since you want to ask it whether it's a temporary ID), then that's what you need to ask for in your key path.

You should read the Key-Value Coding Programming Guide, even if you've read it already, and look up the entity and objectID methods in the NSManagedObject reference. From these, you'll find it clear that Marcus Zarra either mixed the two up or meant objectID but typed entity by accident. It happens to everyone—that's why it's good to always check the docs.