How to assign a value to an object property in the willsave method of the NSManagedObject class?

Question

Objective-C

- (void)willSave {
    self.flag = true;
}

I execute this code and I get an infinite call to the willSave method. How to avoid it?

-(void)willSave {
    NSDate *now = [NSDate date];
    if (self.modificationDate == nil || [now timeIntervalSinceDate:self.modificationDate] > 1.0) {
        self.modificationDate = now;
    }
}

Found this code on stackoverflow, but if I understand correctly, save will be called twice. Could this negatively impact performance?