gistfile1.m

+ (void) insertOrUpdate:(NSArray*)dictArray
           forUniqueKey:(NSString*)key
              withBlock:(void (^) (NSDictionary* dictionary, NSManagedObject* object))block
                inStore:(Store *) store
                  error:(NSError*)error
{
    NSManagedObjectContext* context = [store privateContext];
    __block NSError *localError = nil;
    
    [context performBlockAndWait:^{
        NSSortDescriptor* sortDescriptor = [[NSSortDescriptor alloc] initWithKey:key ascending:YES];
        NSArray* sortedResponse = [dictArray sortedArrayUsingDescriptors:@[sortDescriptor]];
        
        NSArray* fetchedValues = [sortedResponse valueForKeyPath:key];
        
        // Create the fetch request to get all objects matching the unique key.
        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        [fetchRequest setEntity:[self entityWithContext:context]];
        [fetchRequest setPredicate: [NSPredicate predicateWithFormat:@"(%K IN %@)", key, fetchedValues]];
        
        [fetchRequest setSortDescriptors: @[sortDescriptor]];
        
        NSArray *objectsMatchingKey = [context executeFetchRequest:fetchRequest error:&localError];
        if (localError) {
            return;
        }
        
        NSEnumerator* objectEnumerator = [objectsMatchingKey objectEnumerator];
        NSEnumerator* dictionaryEnumerator = [sortedResponse objectEnumerator];
        
        NSDictionary* dictionary;
        id object = [objectEnumerator nextObject];
        SEL selector = NSSelectorFromString(key);

        while (dictionary = [dictionaryEnumerator nextObject]) {
            if (object != nil && [[object performSelector:selector] isEqualToString:dictionary[key]]) {            
                if (block) {
                    block(dictionary, object);
                }
                object = [objectEnumerator nextObject];
            } else {
                id newObject = [object insertInContext:context];
                if (block) {
                    block(dictionary, newObject);
                }
            }
            
        }
        [context save:nil];
    }];
}

Rather than

SEL selector = NSSelectorFromString(key);
[[object performSelector:selector] isEqualToString:dictionary[key]]

Could you not do

[[object valueForKey:key] isEqualToString:dictionary[key]]

Actually you should use valueForKeyPath: for KVC.

Actually you should use valueForKeyPath: for KVC.