private static void ImportMessageToDB(MessageDTO message)
        {
            if (string.IsNullOrWhiteSpace(message.Content))
            {
                throw new ArithmeticException("Content is required");
            }

            if (string.IsNullOrWhiteSpace(message.Recipient))
            {
                throw new ArithmeticException("Recipient is required");
            }

            if (string.IsNullOrWhiteSpace(message.Sender))
            {
                throw new ArithmeticException("Sender is required");
            }

            var context = new ChatSystemContext();

            var recipientId = context.Users
                .Where(u => u.Username == message.Recipient)
                .Select(r => r.Id)
                .FirstOrDefault();

            var senderId = context.Users
                .Where(u => u.Username == message.Sender)
                .Select(s => s.Id)
                .FirstOrDefault();

            var userMessage = new UserMessage()
            {
                Content = message.Content,
                DateTime = message.DateTime,
                RecipientId = recipientId,
                SenderId = senderId
            };

            context.UserMessages.Add(userMessage);
            context.SaveChanges();
        }
        static void Main()
        {
            var context = new ChatSystemContext();

            //            Console.WriteLine(context.Users.Count());

            var channels = context.Channels
                           .Select(c => new
            {
                ChannelName     = c.Name,
                ChannelMessages = c.ChannelMessages
            });

            foreach (var ch in channels)
            {
                Console.WriteLine(ch.ChannelName);
                Console.WriteLine("-- Messages: --");
                foreach (var chMessgae in ch.ChannelMessages)
                {
                    Console.WriteLine("Content: {0}, DateTime: {1}, User: {2}", chMessgae.Content, chMessgae.DateTime, chMessgae.User.Username);
                }
                Console.WriteLine();
            }
        }
        static void Main()
        {
            var context = new ChatSystemContext();

            //            Console.WriteLine(context.Users.Count());

            var channels = context.Channels
                .Select(c => new
                {
                    ChannelName = c.Name,
                    ChannelMessages = c.ChannelMessages
                });

            foreach (var ch in channels)
            {
                Console.WriteLine(ch.ChannelName);
                Console.WriteLine("-- Messages: --");
                foreach (var chMessgae in ch.ChannelMessages)
                {
                    Console.WriteLine("Content: {0}, DateTime: {1}, User: {2}", chMessgae.Content, chMessgae.DateTime, chMessgae.User.Username);
                }
                Console.WriteLine();
            }
        }