pitrou commented on a change in pull request #8366:
URL: https://github.com/apache/arrow/pull/8366#discussion_r500568316
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File path: cpp/src/parquet/arrow/schema.cc
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@@ -689,10 +686,73 @@ Status GetOriginSchema(const std::shared_ptr<const
KeyValueMetadata>& metadata,
// but that is not necessarily present in the field reconstitued from Parquet
data
// (for example, Parquet timestamp types doesn't carry timezone information).
-Status ApplyOriginalStorageMetadata(const Field& origin_field, SchemaField*
inferred) {
+Result<bool> ApplyOriginalMetadata(const Field& origin_field, SchemaField*
inferred);
+
+using NestedFieldRewrapper = std::function<Status(FieldVector, SchemaField*)>;
+
+Status RewrapStructField(FieldVector new_children, SchemaField* inferred) {
+ inferred->field =
inferred->field->WithType(::arrow::struct_(std::move(new_children)));
+ return Status::OK();
+}
+
+Status RewrapListField(FieldVector new_children, SchemaField* inferred) {
+ DCHECK_EQ(new_children.size(), 1);
+ inferred->field = inferred->field->WithType(::arrow::list(new_children[0]));
+ return Status::OK();
+}
+
+// XXX Perhaps add a DataType::WithFields method?
+NestedFieldRewrapper GetNestedFieldRewrapper(const ArrowType& origin_type,
+ const ArrowType& inferred_type) {
+ switch (inferred_type.id()) {
+ case ::arrow::Type::STRUCT:
+ if (origin_type.id() == ::arrow::Type::STRUCT) {
+ return RewrapStructField;
+ }
+ break;
+ case ::arrow::Type::LIST:
+ // TODO also allow LARGE_LIST and FIXED_SIZE_LIST
+ if (origin_type.id() == ::arrow::Type::LIST) {
+ return RewrapListField;
+ }
+ break;
+ default:
+ break;
+ }
+ return {};
+}
+
+Result<bool> ApplyOriginalStorageMetadata(const Field& origin_field,
+ SchemaField* inferred) {
+ bool modified = false;
+
auto origin_type = origin_field.type();
auto inferred_type = inferred->field->type();
+ const int num_children = inferred_type->num_fields();
+
+ if (num_children > 0 && origin_type->num_fields() == num_children) {
+ DCHECK_EQ(static_cast<int>(inferred->children.size()), num_children);
+ const auto nested_rewrapper = GetNestedFieldRewrapper(*origin_type,
*inferred_type);
+ if (nested_rewrapper) {
+ // Apply original metadata recursively to children
+ for (int i = 0; i < inferred_type->num_fields(); ++i) {
+ ARROW_ASSIGN_OR_RAISE(
+ const bool child_modified,
+ ApplyOriginalMetadata(*origin_type->field(i),
&inferred->children[i]));
+ modified |= child_modified;
+ }
+ if (modified) {
+ // Recreate this field using the modified child fields
+ ::arrow::FieldVector modified_children(inferred_type->num_fields());
+ for (int i = 0; i < inferred_type->num_fields(); ++i) {
+ modified_children[i] = inferred->children[i].field;
+ }
+ RETURN_NOT_OK(nested_rewrapper(std::move(modified_children),
inferred));
+ }
+ }
Review comment:
Do you want to try and make this change?
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