public static RowParser <IMaybe <T>, IDataRecord> Optional <T>(RowParser <T, IDataRecord> other)
{
return(new RowParser <IMaybe <T>, IDataRecord>(row =>
{
return other.Parse(row).Map(Maybe.Just).Recover(ex =>
{
if (ex == UnexpectedNullFieldException.UnexpectedNull)
{
return RowParserResult.Successful(Maybe.Nothing <T>());
}
return RowParserResult.Failed <IMaybe <T> >(ex);
});
}));
}
internal static async Task <T> ParseSingle <T>(DbDataReader result, RowParser <T, IDataRecord> parser, CancellationToken ct)
{
var success = await result.ReadAsync(ct);
if (!success)
{
throw new DataException("Expected a single value, but got nothing!");
}
var parseResult = parser.Parse(result).Value;
success = await result.ReadAsync(ct);
if (success)
{
throw new DataException("Expected a single value, but got more than that!");
}
return(parseResult);
}