A better way to deal with mapping dictionaries -> model objects

gistfile1.m

NSString *giIdKey = @"id";
NSString *giJobIdKey = @"job_id";
NSString *giPercentCompleteKey = @"percent_complete";
NSString *giPercentReservedKey = @"percent_reserved";
NSString *giGoalsKey = @"goals";
NSString *giRewardsKey = @"rewards";

@interface ESGroupIncentive()
+ (NSDictionary *)valueMap;
@end

typedef id (^ValueConverter)(id obj);

@implementation ESGroupIncentive

+ (ESGroupIncentive *)fromDictionary:(NSDictionary *)d {
    ESGroupIncentive *gi = [[ESGroupIncentive alloc] init];

    NSDictionary *valueMap = [self valueMap];
    NSDictionary *valueConverters = [self valueConverters];

    for (NSString *key in valueMap) {
        if (d[key]) {

            if (valueConverters[key]) {

                ValueConverter valueConverter = valueConverters[key];
                id value = valueConverter(d[key]);
                [gi setValue:value forKey:valueMap[key]];

            } else {
                [gi setValue:d[key] forKey:valueMap[key]];
            }
        }
    }

    return [gi autorelease];
}

- (id)copyWithZone:(NSZone *)zone {
    ESGroupIncentive *gi = [[ESGroupIncentive allocWithZone:zone] init];
    NSArray *values = [[ESGroupIncentive valueMap] allValues];
    for (NSString *value in values) {
        [gi setValue:[[[self valueForKey:value] copy] autorelease] forKey:value];
    }

    return gi;
}

- (void)encodeWithCoder:(NSCoder *)aCoder {
    NSDictionary *valueMap = [ESGroupIncentive valueMap];
    for (NSString *key in valueMap) {
        [aCoder encodeObject:[self valueForKey:valueMap[key]] forKey:key];
    }
}

- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super init];

    NSDictionary *valueMap = [ESGroupIncentive valueMap];
    for (NSString *key in valueMap) {
        [self setValue:[aDecoder decodeObjectForKey:key] forKey:valueMap[key]];
    }

    return self;
}

+ (NSDictionary *)valueMap {
    return @{giIdKey:@"_groupIncentiveId", giJobIdKey:@"_jobId", giPercentCompleteKey:@"_percentComplete",
         giPercentReservedKey:@"_percentReserved", giGoalsKey:@"_goals", giRewardsKey:@"_rewards", @"date":@"_date"};
}

+ (NSDictionary *)valueConverters {

    return @{@"date": Block_copy(^id (id obj) {
        NSString *value = (NSString *)obj;

        NSDateFormatter *formatter = [ESUtility utcDateFormatter];
        return [formatter dateFromString:value];
    })};

}

- (void)dealloc {
    [_groupIncentiveId release];
    [_jobId release];
    [_percentComplete release];
    [_percentReserved release];
    [_goals release];
    [_rewards release];
    [super dealloc];
}

@end