CurtHagenlocher opened a new issue, #468:
URL: https://github.com/apache/arrow-dotnet/issues/468
### Describe the bug, including details regarding any error messages,
version, and platform.
`ListArray.GetSlicedValues(index)` returns `null` for a non-null element
when the list's `Values` is an `ExtensionArray`, such as a `GuidArray` for a
`list<arrow.uuid>`. It only slices when `Values is Array`:
```csharp
if (!(Values is Array array))
{
return default;
}
```
`ExtensionArray` implements `IArrowArray` but doesn't derive from `Array`,
so a list of extension values looks the same as a null element.
`LargeListArray`, `FixedSizeListArray` and `LargeListViewArray` have the same
check.
Repro (v23.0.0):
```csharp
GuidArray guids = new GuidArray.Builder().Append(Guid.NewGuid()).Build();
ListArray list = new ListArray(
new ListType(new Field("item", GuidType.Default, true)), 1,
new ArrowBuffer.Builder<int>().Append(0).Append(1).Build(),
guids, ArrowBuffer.Empty);
IArrowArray values = list.GetSlicedValues(0); // null; expected a GuidArray
of length 1
```
A fix could slice any `IArrowArray` with `ArrowArrayFactory.Slice(Values,
ValueOffsets[index], GetValueLength(index))`. That builds an extension array
from the sliced `ArrayData`.
Found while adding extension type support to the ADBC ADO.NET client
(apache/arrow-adbc#4919), which works around it for now.
### Component(s)
C#
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