OnlineTickets.cs

using System;
using System.Data.SqlClient;

namespace ddd_patterns.Step2
{
    public class OnlineTickets
    {
        private readonly string _connectionString;

        public OnlineTickets(string connectionString)
        {
            _connectionString = connectionString;
        }

        public Guid AddTicket(Guid attendee)
        {
            var availableTickets = GetAvailableTickets();

            if (availableTickets <= 0)
            {
                throw new Exception("No Ticket available");
            }

            return InsertTicket(attendee);
        }

        private int GetAvailableTickets()
        {
            var availableTickets = 0;
            const string sql1 = @"SELECT get number of available tickets from db";

            using var connection = new SqlConnection(_connectionString);
            var command = new SqlCommand(sql1, connection);
            connection.Open();

            var reader = command.ExecuteReader();

            while (reader.Read())
            {
                availableTickets = reader.GetInt32(0);
            }

            reader.Close();
            return availableTickets;
        }

        private Guid InsertTicket(Guid attendee)
        {
            using var connection = new SqlConnection(_connectionString);
            var tId = Guid.NewGuid();
            const string sql2 = @"Insert into tickets... tId = @tId, aId = @aId";
            var command2 = new SqlCommand(sql2, connection);
            command2.Parameters.AddWithValue("@tId", tId);
            command2.Parameters.AddWithValue("@tad", attendee);
            command2.ExecuteNonQuery();
            return tId;
        }

        public void RemoveTicket(Guid ticket)
        {
            using var connection = new SqlConnection(_connectionString);

            const string sql = @"Delete FROM tickets WHERE tId = @tId";
            var command = new SqlCommand(sql, connection);
            command.Parameters.AddWithValue("@tId", ticket);
            command.ExecuteNonQuery();
        }
    }
}