void initialflightlist()
{
    items = new ObservableCollection<item>();
    OnPropertyChanged("items");

    string connectionString = "##";

    using (OracleConnection connection = new OracleConnection())
    {
        try
        {
            connection.ConnectionString = connectionString;

            using (OracleCommand command = connection.CreateCommand())
            {
                string sql = $"sql";

                command.CommandText = sql;

                if (connection.State != ConnectionState.Open)
                    await connection.OpenAsync();

                DbDataReader reader = await command.ExecuteReaderAsync();
                if (reader.HasRows)
                {
                    while (await reader.ReadAsync())
                    {
                        // Тут я бы добавлял в забинденный к UI список не по одной записи, а пачками по N записей.
                        items.Add(new item
                        {
                            item1 = Convert.ToString(reader["fld1"]),
                            item2 = Convert.ToDateTime(reader["fld2"])
                        });
                    }
                }
            }
        }
        catch (Exception ex)
        {
            //MessageBox.Show(ex.Message);
        }
        finally
        {
            if (connection.State == ConnectionState.Open)
                connection.Close();
        }
    }    
}