private static IEnumerable <IRow> ExtractInternal(IUpdatableRow output, Stream input)
{
if (!input.CanSeek)
{
throw new ArgumentOutOfRangeException(nameof(input), "Input stream must be seekable for ORC reader. Enable the hack to copy to a Memory Stream or to a non-Persisted Memory Mapped file. The hack is the default setting.");
}
using (var fileTail = new FileTail(input))
{
var stripes = fileTail.GetStripeCollection();
var columnsToRead = GetIntersectedColumnMetadata(output.Schema, fileTail).ToArray();
foreach (var stripe in stripes)
{
var extractedColumns = ReadStripe(stripe, columnsToRead).ToArray();
for (int i = 0; i < (int)stripe.NumRows; i++)
{
foreach (var col in extractedColumns)
{
var outputColumn = col.Item1.USqlProjectionColumnIndex;
var value = col.Item2?.GetValue(i) ?? col.Item1.USqlProjectionColumn.DefaultValue;
output.Set(outputColumn, value);
}
yield return(output.AsReadOnly());
}
}
}
}
private static IEnumerable <ProjectedColumnMetadata> GetIntersectedColumnMetadata(ISchema usqlSchema, FileTail orcFileTail)
{
var orcColumnNames = orcFileTail.Footer.Types[0].FieldNames;
var orcColumnMetadata =
orcFileTail.Footer.Types.Skip(1).Select((ct, i) => new
{
ColumnTypeKind = ct.Kind,
OrcColumnName = orcColumnNames[i],
OrcColumnIndex = (uint)(i + 1)
}).ToDictionary(x => x.OrcColumnName, x => x);
for (int i = 0; i < usqlSchema.Count; i++)
{
var uSqlColumn = usqlSchema[i];
if (orcColumnMetadata.ContainsKey(uSqlColumn.Name))
{
var orcMeta = orcColumnMetadata[uSqlColumn.Name];
yield return(new ProjectedColumnMetadata
{
ColumnTypeKind = orcMeta.ColumnTypeKind,
OrcColumnIndex = orcMeta.OrcColumnIndex,
OrcColumnName = orcMeta.OrcColumnName,
USqlProjectionColumn = uSqlColumn,
USqlProjectionColumnIndex = i
});
}
}
}
