viirya commented on code in PR #9445:
URL: https://github.com/apache/arrow-rs/pull/9445#discussion_r3221384624
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arrow-array/src/record_batch.rs:
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@@ -451,6 +513,42 @@ impl RecordBatch {
&mut schema.metadata
}
+ /// Returns the per-batch custom metadata, or `None` if not set.
+ ///
+ /// This corresponds to the `custom_metadata` field on the IPC `Message`
+ /// flatbuffer, separate from schema-level metadata.
+ pub fn custom_metadata(&self) -> Option<&HashMap<String, String>> {
+ self.custom_metadata.as_deref()
+ }
+
+ /// Returns a mutable reference to the per-batch custom metadata,
allocating
+ /// an empty map on first access.
+ ///
+ /// Cheap if this [`RecordBatch`] uniquely owns the metadata; otherwise the
+ /// underlying map is cloned via [`Arc::make_mut`]. An empty map left after
+ /// clearing entries still reports as `Some(_)` from
+ /// [`Self::custom_metadata`]; two batches that differ only in this respect
+ /// still compare equal.
+ pub fn custom_metadata_mut(&mut self) -> &mut HashMap<String, String> {
+ Arc::make_mut(
+ self.custom_metadata
+ .get_or_insert_with(|| Arc::new(HashMap::new())),
+ )
+ }
+
+ /// Sets the per-batch custom metadata, returning `self`.
+ ///
+ /// An empty map is normalized to "no metadata", so a batch built with an
+ /// empty map compares equal to one built without calling this method.
+ pub fn with_custom_metadata(mut self, metadata: HashMap<String, String>)
-> Self {
Review Comment:
Should we use `Arc<HashMap<String, String>>` as the custom metadata type?
Otherwise, if you want to attach same metadata for all record batches, you need
to copy the same metadata map and the `Arc` here is useless as it is only for
one record batch?
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