I need to write a custom setter method for a field (we'll call it foo) in my subclass of NSManagedObject. foo is defined in the data model and Xcode has autogenerated @property and @dynamic fields in the .h and .m files respectively.

If I write my setter like this:

- (void)setFoo: (NSObject *)inFoo {
    [super setFoo: inFoo];
    [self updateStuff];
}

then I get a compiler warning on the call to super.

Alternatively, if I do this:

- (void)setFoo: (NSObject *)inFoo {
    [super setValue: inFoo forKey: inFoo];
    [self updateStuff];
}

then I end up in an infinite loop.

So what's the correct approach to write a custom setter for a subclass of NSManagedObject?