/// <summary>
/// Seeks to the given column. The 4-byte length is read and stored in <see cref="NpgsqlDataReader.ColumnLen"/>.
/// </summary>
internal override async Task SeekToColumn(int column, bool async)
{
if (_column == -1)
{
await Buffer.Ensure(2, async);
_numColumns = Buffer.ReadInt16();
}
if (column < 0 || column >= _numColumns)
{
throw new IndexOutOfRangeException("Column index out of range");
}
if (column < _column)
{
throw new InvalidOperationException($"Invalid attempt to read from column ordinal '{column}'. With CommandBehavior.SequentialAccess, you may only read from column ordinal '{_column}' or greater.");
}
if (column > _column)
{
// Skip to end of column if needed
// TODO: Simplify by better initializing _columnLen/_posInColumn
var remainingInColumn = ColumnLen == -1 ? 0 : ColumnLen - PosInColumn;
if (remainingInColumn > 0)
{
await Buffer.Skip(remainingInColumn, async);
}
// Shut down any streaming going on on the column
if (_stream != null)
{
_stream.Dispose();
_stream = null;
}
// Skip over unwanted fields
for (; _column < column - 1; _column++)
{
await Buffer.Ensure(4, async);
var len = Buffer.ReadInt32();
if (len != -1)
{
await Buffer.Skip(len, async);
}
}
await Buffer.Ensure(4, async);
ColumnLen = Buffer.ReadInt32();
PosInColumn = 0;
_column = column;
}
}
internal override Stream GetStream()
{
Debug.Assert(PosInColumn == 0);
if (_stream != null)
{
throw new InvalidOperationException("Attempt to read a position in the column which has already been read");
}
var stream = new SequentialByteaStream(this);
_stream = stream;
return(stream);
}
internal override async Task <Stream> GetStreamInternal(int column, bool async)
{
CheckRowAndOrdinal(column);
if (_stream != null)
{
throw new InvalidOperationException("Attempt to read a position in the column which has already been read");
}
await SeekToColumn(column, false);
if (ColumnLen == -1)
{
throw new InvalidCastException("Column is null");
}
return(_stream = new SequentialByteaStream(this));
}
internal override async Task ConsumeRow(bool async)
{
if (_column == -1)
{
await Buffer.Ensure(2, async);
_numColumns = Buffer.ReadInt16();
}
if (_stream != null)
{
_stream.Dispose();
_stream = null;
}
// TODO: Potential for code-sharing with ReadColumn above, which also skips
// Skip to end of column if needed
var remainingInColumn = ColumnLen == -1 ? 0 : ColumnLen - PosInColumn;
if (remainingInColumn > 0)
{
await Buffer.Skip(remainingInColumn, async);
}
// Skip over the remaining columns in the row
for (; _column < _numColumns - 1; _column++)
{
await Buffer.Ensure(4, async);
var len = Buffer.ReadInt32();
if (len != -1)
{
await Buffer.Skip(len, async);
}
}
}
internal override Stream GetStream()
{
Contract.Requires(PosInColumn == 0);
if (_stream != null) {
throw new InvalidOperationException("Attempt to read a position in the column which has already been read");
}
var stream = new SequentialByteaStream(this);
_stream = stream;
return stream;
}
