internal static Renting getRentingByUser(string id)
        {
            query = $"SELECT * FROM renting WHERE IDUser = '******';";
            Renting renting = null;

            using (var connection = new NpgsqlConnection(AppSettingProvider.connString))
            {
                connection.Open();
                renting = connection.Query <Renting>(query).FirstOrDefault();
            }
            return(renting);
        }
        internal static void updateRenting(Renting renting)
        {
            query = "UPDATE renting SET " +
                    $"date_to = '{renting.date_to}' " +
                    $"WHERE ID_Renting = '{renting.ID_Renting}';";

            var id = -1;

            using (var connection = new NpgsqlConnection(AppSettingProvider.connString))
            {
                connection.Open();
                id = connection.ExecuteScalar <int>(query, renting);
            }
        }
        internal static async Task <int> createRenting(Renting renting)
        {
            query = "INSERT INTO renting " +
                    "(IDAp, IDUser, date_from, date_to) " +
                    "VALUES " +
                    $"({renting.IDAp}, '{renting.IDUser}', '{renting.date_from}', '{renting.date_to}') " +
                    "RETURNING ID_Renting;";

            int id = -1;

            using (var connection = new NpgsqlConnection(AppSettingProvider.connString))
            {
                connection.Open();
                id = await connection.ExecuteScalarAsync <int>(query, renting);
            }
            return(id);
        }