Fast CoreData parsing helper method (uses MagicalRecord 2.x)

CoreDataParsingHelper.m

/**
 * returns the dictionary of updated or created managed objects where the key is object's entityIdentifierKey value
 * requires identifier to be unique
 * parsingBlock needs to implement the updating of each object from with assosiated dictionary
 */
+ (NSDictionary *)parseObjectsForClass:(Class)objectClass
                             fromArray:(NSArray *)array
                   entityIdentifierKey:(NSString *)entityIdentifierKey
                     dictIdentifierKey:(NSString *)dictIdentifierKey
                       deleteUnmatched:(BOOL)deleteUnmatched
                             inContext:(NSManagedObjectContext *)context
                          parsingBlock:(void(^)(id object, BOOL isCreated, NSDictionary *dict))parsingBlock {

    NSArray *existingObjects = [[objectClass class] MR_findAllInContext:context];
    NSArray *existingIdentifiers = [existingObjects valueForKey:entityIdentifierKey];
    NSMutableDictionary *existingObjectsByID = [NSMutableDictionary dictionaryWithObjects:existingObjects
                                                                                  forKeys:existingIdentifiers];
    
    NSMutableDictionary *parsedObjects = [NSMutableDictionary dictionaryWithCapacity:array.count];
    for (NSDictionary *dict in array) {
        NSNumber *identifier = dict[dictIdentifierKey];
        if ([identifier isEqual:[NSNull null]]) {
            continue;
        }
        id object = existingObjectsByID[identifier];
        BOOL created = NO;
        if (object) {
            [existingObjectsByID removeObjectForKey:identifier];
        } else {
            created = YES;
            object = [[objectClass class] MR_createInContext:context];
            [object setValue:identifier forKey:entityIdentifierKey];
        }
        if (parsingBlock) {
            parsingBlock(object, created, dict);
        }
        parsedObjects[identifier] = object;
    }
    if (deleteUnmatched) {
        for (id objectToDelete in existingObjectsByID.allValues) {
            [objectToDelete MR_deleteInContext:context];
        }
    }
    return parsedObjects;
}