Xcode 10 Error: Multiple commands produce after generating NSManagedObject subclass

Question

I have a project to which I want to use CoreData. I first create the data model - the code compiles fine. Then, I try to generate the NSManagedObject subclasses by going to Editor -> Create NSManagedObject Subclass . The generated files causes Multiple commands produce error when trying to compile.

Answer 1

Since you've generated the NSManagedObject subclasses manually (by going to Editor -> Create NSManagedObject Subclass ), you need to tell CoreData that it shouldn't generate them again when building the project.

You do that by going to your data model file (something like Model.xcdatamodeld ), and on the Data Model Inspector change Codegen from Class Definition to either Category/Extension or (most probably) Manual/None :

Note: You might have to delete your DerivedData after doing this.

See section "Xcode automatic subclass generation" at What's New In Core Data for more information.