mantleRails.m

+ (NSDateFormatter *)dateFormatter {
    return [[ISO8601DateFormatter alloc] init];
}

+ (NSValueTransformer *)jsonDateValueTransformer {
    return [MTLValueTransformer reversibleTransformerWithForwardBlock:^(NSString *str) {
        return [self.dateFormatter dateFromString:str];
    } reverseBlock:^(NSDate *date) {
        return [self.dateFormatter stringFromDate:date];
    }];
}

+ (NSValueTransformer *)urlValueTransformer {
    return [MTLValueTransformer reversibleTransformerWithForwardBlock:^NSURL *(NSString *url) {
        return [NSURL URLWithString:url];
    } reverseBlock:^NSString *(NSURL *url) {
        return [url absoluteString];
    }];
}

/** Returns a rails-compatible transformer if the property has a class of NSDate or NSURL */
+ (NSValueTransformer *)JSONTransformerForKey:(NSString *)key {
    objc_property_t property = class_getProperty([self class], [key cStringUsingEncoding:NSUTF8StringEncoding]);
    mtl_propertyAttributes *attributes = mtl_copyPropertyAttributes(property);
    @try {
        if ([attributes->objectClass isSubclassOfClass:[NSDate class]]) {
            return [self jsonDateValueTransformer];
        } else if ([attributes->objectClass isSubclassOfClass:[NSURL class]]) {
            return [self urlValueTransformer];
        } else {
            return nil;
        }
    } @finally {
        if (attributes) free(attributes);
    }
}