liamzwbao commented on code in PR #8768:
URL: https://github.com/apache/arrow-rs/pull/8768#discussion_r2492349064
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parquet-variant-compute/src/variant_to_arrow.rs:
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@@ -60,6 +61,9 @@ pub(crate) enum PrimitiveVariantToArrowRowBuilder<'a> {
TimestampNanoNtz(VariantToTimestampNtzArrowRowBuilder<'a,
datatypes::TimestampNanosecondType>),
Time(VariantToPrimitiveArrowRowBuilder<'a,
datatypes::Time64MicrosecondType>),
Date(VariantToPrimitiveArrowRowBuilder<'a, datatypes::Date32Type>),
+ Utf8(VariantToUtf8ArrowRowBuilder<'a, i32>),
+ LargeUtf8(VariantToUtf8ArrowRowBuilder<'a, i64>),
+ Binary(VariantToBinaryArrowRowBuilder<'a>),
Review Comment:
Agreed on the first one as we may not need metadata column if explicitly
cast to Binary.
For the 2nd, I think the primitive is for arrow because we check
`is_primitive` and will throw error if the request data type is not primitive
[here](https://github.com/apache/arrow-rs/blob/6be6cbadf1f9bc0705b0aa97ca434ae3677ed43f/parquet-variant-compute/src/variant_to_arrow.rs#L325-L334).
Also based on the definition
[here](https://github.com/apache/arrow-rs/blob/6be6cbadf1f9bc0705b0aa97ca434ae3677ed43f/parquet-variant-compute/src/variant_to_arrow.rs#L36),
this builder is to convert variant values to primitive arrow. Given that,
having `Null/Boolean/Uuid` in this builder makes the intent tricky. I’d prefer
we rename the builder and update the docs as needed. We don't need a separate
builder tho as we can reuse a lot of codes here.
For Variant primitive, we had a related
[discussion](https://github.com/apache/arrow-rs/pull/8600#discussion_r2442296788)
before. I think Parquet enforces primitive types at write time and unshred to
ensure valid data. But for `variant_get`, it’s reasonable to allow casting to
any valid Arrow datatype, even those without a direct Variant-primitive
counterpart (e.g., `Decimal256` or `LargeUtf8`).
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