jecsand838 commented on code in PR #8274:
URL: https://github.com/apache/arrow-rs/pull/8274#discussion_r2322622541
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arrow-avro/src/schema.rs:
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@@ -370,6 +371,49 @@ impl AvroSchema {
pub fn fingerprint(&self) -> Result<Fingerprint, ArrowError> {
generate_fingerprint_rabin(&self.schema()?)
}
+
+ /// Build Avro JSON from an Arrow [`ArrowSchema`], applying the given
null‑union order.
+ ///
+ /// If the input Arrow schema already contains Avro JSON in
+ /// [`SCHEMA_METADATA_KEY`], that JSON is returned verbatim to preserve
+ /// the exact header encoding alignment; otherwise, a new JSON is
generated
+ /// honoring `null_union_order` at **all nullable sites**.
+ pub fn from_arrow_with_options(
+ schema: &ArrowSchema,
+ null_union_order: Option<Nullability>,
+ ) -> Result<AvroSchema, ArrowError> {
+ if let Some(json) = schema.metadata.get(SCHEMA_METADATA_KEY) {
+ return Ok(AvroSchema::new(json.clone()));
+ }
+ let order = null_union_order.unwrap_or(Nullability::NullFirst);
+ let mut name_gen = NameGenerator::default();
+ let fields_json = schema
+ .fields()
+ .iter()
+ .map(|f| arrow_field_to_avro_with_order(f, &mut name_gen, order))
+ .collect::<Result<Vec<_>, _>>()?;
+ let record_name = schema
+ .metadata
+ .get(AVRO_NAME_METADATA_KEY)
+ .map_or("topLevelRecord", |s| s.as_str());
Review Comment:
> aside: Is this a well-known default name? Or just an arbitrary naming
choice by this package?
While not an Avro‑spec default, `topLevelRecord` is used as a de‑facto
default because several popular tools (notably Spark/Databricks) default to the
same name when they synthesize an Avro schema from a struct/row.
> And does it actually matter in practice? (I guess if it mattered, the
schema metadata would say so)?
Avro requires that a record have a name to be valid. Also because the record
name participates in canonical form parsing, changing a record's name will
change it's fingerprint.
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