public static LastReadedMessage GetLastReadedMessageForEmloyee(IUnitOfWork uow, ChatClass chat, Employee employee)
        {
            LastReadedMessage lastReadedAlias = null;

            return uow.Session.QueryOver<LastReadedMessage> (() => lastReadedAlias)
                .Where (() => lastReadedAlias.Chat.Id == chat.Id)
                .Where (() => lastReadedAlias.Employee.Id == employee.Id)
                .SingleOrDefault();
        }
        public static int GetLastReadedMessagesCountForEmployee(IUnitOfWork uow, ChatClass chat, Employee employee)
        {
            LastReadedMessage lastReadedAlias = null;
            ChatMessage chatMessageAlias = null;
            var lastMessage = GetLastReadedMessageForEmloyee(uow, chat, employee);

            var query = uow.Session.QueryOver<ChatMessage>(() => chatMessageAlias)
                .Where(() => chatMessageAlias.Chat.Id == chat.Id);
            if (lastMessage == null)
                return query.RowCount();
            else
                return query
                    .Where(() => chatMessageAlias.DateTime > lastMessage.LastDateTime)
                    .RowCount();
        }