westonpace commented on code in PR #35860:
URL: https://github.com/apache/arrow/pull/35860#discussion_r1213340455
##########
cpp/src/arrow/dataset/file_base.cc:
##########
@@ -475,16 +475,38 @@ Result<acero::ExecNode*> MakeWriteNode(acero::ExecPlan*
plan,
const WriteNodeOptions write_node_options =
checked_cast<const WriteNodeOptions&>(options);
- const std::shared_ptr<const KeyValueMetadata>& custom_metadata =
- write_node_options.custom_metadata;
+ const std::shared_ptr<Schema>& custom_schema =
write_node_options.custom_schema;
const FileSystemDatasetWriteOptions& write_options =
write_node_options.write_options;
+ const std::shared_ptr<Schema>& input_schema = inputs[0]->output_schema();
+
+ if (custom_schema != nullptr) {
+ if (custom_schema->num_fields() != input_schema->num_fields()) {
+ return Status::Invalid(
+ "The provided custom_schema did not have the same number of fields
as the "
+ "data. The custom schema can only be used to add metadata /
nullability to "
+ "fields and cannot change the type or number of fields.");
+ }
+ for (int field_idx = 0; field_idx < input_schema->num_fields();
field_idx++) {
+ if (!input_schema->field(field_idx)->type()->Equals(
+ custom_schema->field(field_idx)->type())) {
Review Comment:
Changing the names should be safe. Admittedly, a user could also do this
name change by inserting a project node before the write node.
I could be convinced otherwise but I don't think this does any harm and I
think, as a user, I would expect this behavior, so it wouldn't be surprising
that the names changed.
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