[GitHub] [arrow-rs] alamb commented on a diff in pull request #3953: Don't discard nulls converting StructArray to RecordBatch (#3951)

["alamb (via GitHub)" <gi...@apache.org>]

alamb commented on code in PR #3953:
URL: https://github.com/apache/arrow-rs/pull/3953#discussion_r1153489207


##########
arrow-array/src/array/struct_array.rs:
##########
@@ -89,6 +89,14 @@ impl StructArray {
         }
     }
 
+    /// Returns the [`Field`] of this [`StructArray`]
+    pub fn fields(&self) -> &[Field] {

Review Comment:
   I wonder if this needs to be updated to avoid a logical conflict with `FieldList`



##########
arrow-array/src/record_batch.rs:
##########
@@ -447,23 +447,28 @@ impl Default for RecordBatchOptions {
         Self::new()
     }
 }
+impl From<StructArray> for RecordBatch {
+    fn from(value: StructArray) -> Self {
+        assert_eq!(
+            value.null_count(),
+            0,
+            "Cannot convert nullable StructArray to RecordBatch"

Review Comment:
   I don't understand why this is an error
   
   Wouldn't it make more sense to apply  the parent `StructArray` validity mask to each child's mask to form a new mask that is only non null if both the struct array and the child array were non null 🤔 



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