[GitHub] [arrow] pitrou commented on a change in pull request #8939: ARROW-10928: [C++] Better Parquet error when trying to write empty struct

[GitBox <gi...@apache.org>]

pitrou commented on a change in pull request #8939:
URL: https://github.com/apache/arrow/pull/8939#discussion_r544488560



##########
File path: cpp/src/parquet/arrow/schema.cc
##########
@@ -113,12 +114,21 @@ Status StructToNode(const std::shared_ptr<::arrow::StructType>& type,
                     const WriterProperties& properties,
                     const ArrowWriterProperties& arrow_properties, NodePtr* out) {
   std::vector<NodePtr> children(type->num_fields());
-  for (int i = 0; i < type->num_fields(); i++) {
-    RETURN_NOT_OK(FieldToNode(type->field(i)->name(), type->field(i), properties,
-                              arrow_properties, &children[i]));
+  if (type->num_fields() != 0) {
+    for (int i = 0; i < type->num_fields(); i++) {
+      RETURN_NOT_OK(FieldToNode(type->field(i)->name(), type->field(i), properties,
+                                arrow_properties, &children[i]));
+    }
+  } else {
+    // XXX (ARROW-10928) We could add a dummy primitive node but that would
+    // require special handling when writing and reading, to avoid column index
+    // mismatches.
+    return Status::NotImplemented(
+        "Cannot write struct type with no child fields to Parquet. "

Review comment:
       Hmm, I can add the struct field name to the message, but I'm not sure I understand the suggestion about "dummy".




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