Modify your toNSDictionary
method:
- (NSMutableDictionary *)toNSDictionary
{
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
[dictionary setValue:self.OrderId forKey:@"OrderId"];
[dictionary setValue:self.Title forKey:@"Title"];
[dictionary setValue:self.Weight forKey:@"Weight"];
NSMutableDictionary *userDictionary = [NSMutableDictionary dictionary];
[userDictionary setValue:self.User.someProperty1 forKey:@"someProperty1"];
[userDictionary setValue:self.User.someProperty2 forKey:@"someProperty2"];
[dictionary setValue:userDictionary forKey:@"User"];
return dictionary;
}