I have a fetch request defined within my core data model called "RemainingGaneProjections". I want to execute that fetch request and sort the results by one of the entity's attributes. My code looks like this:

NSFetchRequest *projectionsRequest = [model fetchRequestTemplateForName:@"RemainingGameProjections"];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"confidence" ascending:NO];
[projectionsRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];

When I try to execute this code it crashes with the following message:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Can't modify a named fetch request in an immutable model.'

I have confirmed in the debugger that this crash happens when I execute the setSortDescriptors method on my NSFetchRequest. I haven't been able to figure out why this happens.

Any explanations for what is happening here? Is there another approach I should be using when retrieving data that needs to be sorted?

objective-c core-data
Edit
Report