AppServiceUtilities.cs

        public static void SaveUser(User userToSave)
        {
            using (var assembleContainer = BuildAssembleContainer())
            {
                var userRepository = assembleContainer.Resolve<IUserRepository>();
                var user = userRepository.GetById(userToSave.Id);

                if (user == null)
                {
                    throw new ArgumentException(string.Format("A User with id={0} does not exist in the database", userToSave.Id));
                }

                userRepository.InsertOrUpdate(user);
            }
        }