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Make HasRows report whether rows exist #1288

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ad32f38
Make HasRows report whether rows exist
alaricd Oct 20, 2026
a31867d
Keep stored procedure output when HasRows peeks
alaricd Nov 4, 2026
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84 changes: 84 additions & 0 deletions src/FirebirdSql.Data.FirebirdClient.Tests/FbDataReaderTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,90 @@ public async Task ReadTest()
}
}

[Test]
public async Task HasRowsIsFalseForAnEmptyResultTest()
{
// DbDataReader.HasRows: "true if the DbDataReader contains one or more rows; otherwise false."
await using (var command = new FbCommand("select INT_FIELD from TEST where 1 = 0", Connection))
{
await using (var reader = await command.ExecuteReaderAsync())
{
Assert.IsFalse(reader.HasRows);
Assert.IsFalse(await reader.ReadAsync());
}
}
}

[Test]
public async Task HasRowsDoesNotSkipTheFirstRowTest()
{
await using (var command = new FbCommand("select INT_FIELD from TEST where INT_FIELD in (1, 2) order by INT_FIELD", Connection))
{
await using (var reader = await command.ExecuteReaderAsync())
{
Assert.IsTrue(reader.HasRows);
Assert.IsTrue(await reader.ReadAsync());
Assert.AreEqual(1, reader.GetInt32(0));
Assert.IsTrue(reader.Read());
Assert.AreEqual(2, reader.GetInt32(0));
Assert.IsFalse(reader.Read());
Assert.IsTrue(reader.HasRows, "HasRows describes the result, not the current position");
}
}
}

[Test]
public async Task HasRowsThenCloseKeepsStoredProcedureOutputParametersTest()
{
await using (var create = Connection.CreateCommand())
{
create.CommandText = "RECREATE PROCEDURE HASROWS_OUTPUT (P1 INTEGER) RETURNS (R1 INTEGER) AS BEGIN R1 = P1 * 2; END";
await create.ExecuteNonQueryAsync();
}

await using (var command = new FbCommand("EXECUTE PROCEDURE HASROWS_OUTPUT(?)", Connection))
{
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add("P1", FbDbType.Integer).Value = 21;
var output = command.Parameters.Add("R1", FbDbType.Integer);
output.Direction = ParameterDirection.Output;

await using (var reader = await command.ExecuteReaderAsync())
{
Assert.IsTrue(reader.HasRows);
await reader.CloseAsync();
}

Assert.AreEqual(42, output.Value, "HasRows must not consume the stored procedure output row");
}
}

[Test]
public void HasRowsThenCloseKeepsStoredProcedureOutputParametersSyncTest()
{
using (var create = Connection.CreateCommand())
{
create.CommandText = "RECREATE PROCEDURE HASROWS_OUTPUT (P1 INTEGER) RETURNS (R1 INTEGER) AS BEGIN R1 = P1 * 2; END";
create.ExecuteNonQuery();
}

using (var command = new FbCommand("EXECUTE PROCEDURE HASROWS_OUTPUT(?)", Connection))
{
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add("P1", FbDbType.Integer).Value = 21;
var output = command.Parameters.Add("R1", FbDbType.Integer);
output.Direction = ParameterDirection.Output;

using (var reader = command.ExecuteReader())
{
Assert.IsTrue(reader.HasRows);
reader.Close();
}

Assert.AreEqual(42, output.Value, "HasRows must not consume the stored procedure output row");
}
}

[Test]
public async Task ReadClobTest()
{
Expand Down
49 changes: 44 additions & 5 deletions src/FirebirdSql.Data.FirebirdClient/FirebirdClient/FbDataReader.cs
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Expand Up @@ -51,6 +51,12 @@ public sealed class FbDataReader : DbDataReader
private bool _eof;
private bool _isClosed;
private int _position;
// Row fetched ahead by HasRows. _hasPeekedRow is needed because a peek that found nothing
// leaves _peekedRow null, and that must still count as "already fetched" so the statement is not
// fetched again. _peekedRow is only non-null while _hasPeekedRow is true.
private DbValue[] _peekedRow;
private bool _hasPeekedRow;
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private bool _hasRows;
private int _recordsAffected;
private Dictionary<string, int> _columnsIndexesOrdinal;
private Dictionary<string, int> _columnsIndexesOrdinalCI;
Expand Down Expand Up @@ -102,9 +108,25 @@ public override int Depth
}
}

/// <summary>
/// DbDataReader.HasRows: "true if the DbDataReader contains one or more rows; otherwise false." Before the first
/// Read this fetches one row ahead; Read then returns that row.
/// </summary>
public override bool HasRows
{
get { return _command.HasFields; }
get
{
if (!_hasRows && !_isClosed && !_hasPeekedRow && _position == StartPosition && _command != null && _command.HasFields && !IsCommandBehavior(CommandBehavior.SchemaOnly))
{
using (var explicitCancellation = ExplicitCancellation.Enter(CancellationToken.None, _command.Cancel))
{
_peekedRow = _command.Fetch();
}
_hasPeekedRow = true;
_hasRows = _peekedRow != null;
}
return _hasRows;
}
}

public override bool IsClosed
Expand Down Expand Up @@ -150,7 +172,8 @@ public override void Close()
{
if (_command.CommandType == CommandType.StoredProcedure)
{
_command.SetOutputParameters();
// HasRows may already have fetched the output row; hand it over rather than losing it.
_command.SetOutputParameters(_peekedRow);
}
if (_command.HasImplicitTransaction)
{
Expand All @@ -166,6 +189,8 @@ public override void Close()
_command = null;
_connection = null;
_row = null;
_peekedRow = null;
_hasPeekedRow = false;
_schemaTable = null;
_fields = null;
}
Expand All @@ -179,7 +204,8 @@ public override async Task CloseAsync()
{
if (_command.CommandType == CommandType.StoredProcedure)
{
await _command.SetOutputParametersAsync(CancellationToken.None).ConfigureAwait(false);
// HasRows may already have fetched the output row; hand it over rather than losing it.
await _command.SetOutputParametersAsync(_peekedRow, CancellationToken.None).ConfigureAwait(false);
}
if (_command.HasImplicitTransaction)
{
Expand All @@ -195,6 +221,8 @@ public override async Task CloseAsync()
_command = null;
_connection = null;
_row = null;
_peekedRow = null;
_hasPeekedRow = false;
_schemaTable = null;
_fields = null;
}
Expand Down Expand Up @@ -229,10 +257,11 @@ public override bool Read()
{
using (var explicitCancellation = ExplicitCancellation.Enter(CancellationToken.None, _command.Cancel))
{
_row = _command.Fetch();
_row = TakePeekedRow(out var peeked) ? peeked : _command.Fetch();
if (_row != null)
{
_position++;
_hasRows = true;
return true;
}
else
Expand All @@ -259,10 +288,11 @@ public override async Task<bool> ReadAsync(CancellationToken cancellationToken)
{
using (var explicitCancellation = ExplicitCancellation.Enter(cancellationToken, _command.Cancel))
{
_row = await _command.FetchAsync(explicitCancellation.CancellationToken).ConfigureAwait(false);
_row = TakePeekedRow(out var peeked) ? peeked : await _command.FetchAsync(explicitCancellation.CancellationToken).ConfigureAwait(false);
if (_row != null)
{
_position++;
_hasRows = true;
return true;
}
else
Expand Down Expand Up @@ -1012,6 +1042,15 @@ private FbDbType GetProviderType(int i)
return (FbDbType)_fields[i].DbDataType;
}

private bool TakePeekedRow(out DbValue[] row)
{
row = _peekedRow;
var hadPeekedRow = _hasPeekedRow;
_peekedRow = null;
_hasPeekedRow = false;
return hadPeekedRow;
}

private void UpdateRecordsAffected()
{
if (_command != null && !_command.IsDisposed)
Expand Down
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