public bool Create(Performer performer)
        {
            if (performer.Id == 0)
            {
                var sql = string.Format("INSERT INTO Performers " +
                                        "(Name, Surname, Patronymic) VALUES(@Name, @Surname, @Patronymic)");

                using (var connection = new SqlConnection())
                {
                    connection.ConnectionString = ConnectionString;
                    connection.Open();

                    using (var command = new SqlCommand(sql, connection))
                    {
                        command.Parameters.AddWithValue("@Name", performer.Name);
                        command.Parameters.AddWithValue("@Surname", performer.Surname);
                        command.Parameters.AddWithValue("@Patronymic", performer.Patronymic);

                        command.ExecuteNonQuery();
                    }
                    connection.Close();
                }
                return true;
            }
            return false;
        }
        public IEnumerable<Performer> GetAllPerformers()
        {
            var allPerformers = new List<Performer>();

            using (var connection = new SqlConnection())
            {
                connection.ConnectionString = ConnectionString;
                connection.Open();

                const string strSql = "SELECT * FROM Performers";
                var command = new SqlCommand(strSql, connection);
                var dataReader = command.ExecuteReader(CommandBehavior.CloseConnection);

                if (dataReader.HasRows)
                {
                    while (dataReader.Read())
                    {
                        var performer = new Performer
                        {
                            Id = dataReader.GetInt32(0),
                            Name = dataReader.GetString(1),
                            Surname = dataReader.GetString(2),
                            Patronymic = dataReader.GetString(3)
                        };
                        allPerformers.Add(performer);
                    }
                }
                else
                {
                    connection.Close();
                    return null;
                }

                connection.Close();
            }

            return allPerformers;
        }