ewoodbury commented on code in PR #3255:
URL: https://github.com/apache/iceberg-rust/pull/3255#discussion_r4235440362
##########
crates/iceberg/src/arrow/record_batch_transformer.rs:
##########
@@ -193,6 +195,284 @@ pub(crate) enum ColumnSource {
// post-processing step by using the projection mask.
}
+/// Reconciles a source array to the target type by matching nested fields on
+/// field id rather than position, mirroring iceberg-java's nested readers.
+///
+/// The plan is resolved once per file, when the `BatchTransform` is built, so
+/// applying it per batch is just index lookups and array assembly.
+#[derive(Debug)]
+pub(crate) enum PromotePlan {
+ PassThrough,
+ Cast(DataType),
+ Struct {
+ fields: Fields,
+ children: Vec<ChildPlan>,
+ },
+ List {
+ field: FieldRef,
+ element: Box<PromotePlan>,
+ },
+ Map {
+ field: FieldRef,
+ entry_fields: Fields,
+ entries: Vec<ChildPlan>,
+ sorted: bool,
+ },
+}
+
+#[derive(Debug)]
+pub(crate) enum ChildPlan {
+ FromSource {
+ source_index: usize,
+ plan: PromotePlan,
+ },
+ Add {
+ target_type: DataType,
+ value: Option<PrimitiveLiteral>,
+ },
+}
+
+impl PromotePlan {
+ fn build(
+ source: &DataType,
+ target: &DataType,
+ snapshot_schema: &IcebergSchema,
+ constant_fields: &HashMap<i32, ColumnConstant>,
+ ) -> Result<Self> {
+ if source == target {
+ return Ok(PromotePlan::PassThrough);
+ }
+ match (source, target) {
+ (DataType::Struct(source_fields), DataType::Struct(target_fields))
=> {
+ Ok(PromotePlan::Struct {
+ children: Self::build_struct_children(
+ source_fields,
+ target_fields,
+ snapshot_schema,
+ constant_fields,
+ )?,
+ fields: target_fields.clone(),
+ })
+ }
+ // A file's Arrow schema hint can give either offset width;
`apply` converts it.
+ // Table schemas are always `List`
(`ToArrowSchemaConverter::list`).
+ (
+ DataType::List(source_field) |
DataType::LargeList(source_field),
+ DataType::List(target_field),
+ ) => Ok(PromotePlan::List {
+ element: Box::new(Self::build(
+ source_field.data_type(),
+ target_field.data_type(),
+ snapshot_schema,
+ constant_fields,
+ )?),
+ field: target_field.clone(),
+ }),
+ (DataType::Map(source_entries, _), DataType::Map(target_entries,
sorted)) => {
+ match (source_entries.data_type(), target_entries.data_type())
{
+ (DataType::Struct(source_fields),
DataType::Struct(target_fields)) => {
+ Ok(PromotePlan::Map {
+ entries: Self::build_struct_children(
+ source_fields,
+ target_fields,
+ snapshot_schema,
+ constant_fields,
+ )?,
+ entry_fields: target_fields.clone(),
+ field: target_entries.clone(),
+ sorted: *sorted,
+ })
+ }
+ _ => Err(Error::new(
+ ErrorKind::Unexpected,
+ format!(
+ "expected struct-typed map entries, got
{source_entries:?} and {target_entries:?}"
+ ),
+ )),
+ }
+ }
+ (_, DataType::Struct(_) | DataType::List(_) |
DataType::LargeList(_))
+ | (_, DataType::Map(_, _)) => {
+ Err(invalid_data!("cannot promote {source:?} to {target:?}"))
Review Comment:
Done in f136c367f. A struct/list/map source against a target of a different
kind now errors when the plan is built, so zero-row files fail too. Reads that
work today still go through the same-kind and `LargeList` -> `List` arms; the
only cast this now rejects is list -> string, which isn't a valid promotion.
Covered in `promote_rejects_invalid_source_at_build
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