Clarifications on NSConfinementConcurrencyType context as child of a parent context

Question

While reading the doc about NSConfinementConcurrencyType, I read the following

You cannot use this concurrency type in conjunction with the new nested contexts feature

This sentence is quite weird to me since I can do, for example, within an NSOperation subclass like

NSManagedObjectContext * localMOC = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSConfinementConcurrencyType];
[localMOC setParentContext:[self mainContext]];

where the mainContext can be injected from outside and is of type NSMainQueueConcurrencyType.

Am I missing something?

Answer 1

Yes, that documentation is poorly worded.

What I think it means is that you cannot use:

NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
[moc setParentContext:[self managedObjectContext]];

Which I have tested previously and it did fail with an error. YMMV of course as I tested it in iOS 5.x.

That is different than:

NSManagedObjectContext * localMOC = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSConfinementConcurrencyType];
[localMOC setParentContext:[self mainContext]];

Which works just fine and is part of the newer Core Data design.

There is a subtle difference between the two initializers and the older, historic, initializer is missing some key component to allow parent-child contexts to work properly.