[alaricd]

Problem

DbDataReader.GetFieldValue<byte[]>() on DuckDB BLOB columns returned the provider's Stream value, causing an invalid cast for consumers that request materialized bytes.

Fix

• Materialize BLOB data as byte[] for GetFieldValue<byte[]>().
• Preserve existing GetValue() and GetStream() behavior as streams.
• Add coverage for non-empty and empty BLOBs.

Validation

• DuckDB blob tests: 6 passed.
• Focused coverage: new GetBytes method 100% line, branch, and method coverage.
• ADO.NET conformance test added separately and passes on .NET 8 and .NET 10.

[coveralls]

Coverage Report for CI Build 40294592054

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage increased (+0.1%) to 92.914%

Details

• Coverage increased (+0.1%) from the base build.
• Patch coverage: 6 of 6 lines across 1 file are fully covered (100%).
• 13 coverage regressions across 4 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

13 previously-covered lines in 4 files lost coverage.

File	Lines Losing Coverage	Coverage
DuckDB.NET.Data/DataChunk/Reader/VectorDataReaderBase.cs	4	92.88%
DuckDB.NET.Data/DuckDBDataReader.cs	3	97.18%
DuckDB.NET.Data/DuckDBTransaction.cs	3	87.8%
DuckDB.NET.Data/PreparedStatement/PreparedStatement.cs	3	93.18%

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Coverage Stats

Relevant Lines:	4287
Covered Lines:	4046
Line Coverage:	94.38%
Relevant Branches:	2572
Covered Branches:	2327
Branch Coverage:	90.47%
Branches in Coverage %:	Yes
Coverage Strength:	967896.98 hits per line

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💛 - Coveralls

[Giorgi]

Thanks for this! Reading a BLOB as byte[] is a gap people hit often, and the change is small and fits the reader's conventions (typeof(T) == typeof(byte[]), nothing else in the type test).

One thing should be fixed before merging, and two smaller ones would be nice to have.

1. The object path still returns a Stream for a byte[] target

The PR changes the typed path (GetValidValue<T>). The override GetValue(ulong offset, Type targetType) still has DuckDBType.Blob => GetStream(offset) for every target type.

The composite readers read their children through that object path, so a BLOB inside a struct, map or list still fails:

• Struct: a byte[] property is read with reader.GetValue(offset, property.PropertyType), gets a Stream, and the setter's cast throws InvalidCastException.
• Map: for Dictionary<string, byte[]>, the values are read with valueReader.GetValue(childOffset, valueTargetType), and adding a Stream through IDictionary.Add throws.
• List: List<byte[]> goes through BuildOtherList, whose items come from the same GetValue(…, typeof(byte[])).

So reader.GetFieldValue<byte[]>(0) works, but GetFieldValue<List<byte[]>>(0) and a struct with a byte[] property don't. (I worked this out from the code; I haven't run the branch.)

The same branch in the object path fixes it. GetValue(offset) asks for the column's own type, Stream, so GetValue() still returns a stream:

DuckDBType.Blob => targetType == typeof(byte[]) ? GetBytes(offset) : GetStream(offset),

Could you add tests for a BLOB struct field read into a byte[] property, a MAP(VARCHAR, BLOB) read as Dictionary<string, byte[]>, and a BLOB[] read as List<byte[]>?

2. GetBytes can copy straight from the string data

There's no need for a stream just to read it into an array:

private unsafe byte[] GetBytes(ulong offset)
{
    var data = (DuckDBString*)DataPointer + offset;
    return new ReadOnlySpan<byte>((void*)data->Data, checked((int)data->Length)).ToArray();
}

3. Tests

The two new tests (non-empty and empty BLOB) look good. One more assertion, reader.GetValue(0).Should().BeOfType<UnmanagedMemoryStream>() next to the byte[] read, would pin that GetValue() is unchanged, as the description says.

Docs: once this is in, I'll add byte[] for BLOB to docs/type-mapping.md in the docs repository.