[GitHub] [arrow] pitrou commented on a diff in pull request #12829: ARROW-16116: [C++] Handle non-nullable fields when reading Parquet

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

pitrou commented on code in PR #12829:
URL: https://github.com/apache/arrow/pull/12829#discussion_r860676066


##########
cpp/src/parquet/arrow/reader_internal.cc:
##########
@@ -434,14 +480,26 @@ Status TransferBinary(RecordReader* reader, MemoryPool* pool,
   DCHECK(binary_reader);
   auto chunks = binary_reader->GetBuilderChunks();
   for (auto& chunk : chunks) {
-    if (!chunk->type()->Equals(*logical_value_type)) {
+    if (!chunk->type()->Equals(*logical_type_field->type())) {
       // XXX: if a LargeBinary chunk is larger than 2GB, the MSBs of offsets
       // will be lost because they are first created as int32 and then cast to int64.
       ARROW_ASSIGN_OR_RAISE(
-          chunk, ::arrow::compute::Cast(*chunk, logical_value_type, cast_options, &ctx));
+          chunk,
+          ::arrow::compute::Cast(*chunk, logical_type_field->type(), cast_options, &ctx));
     }
   }
-  *out = std::make_shared<ChunkedArray>(chunks, logical_value_type);
+  if (!logical_type_field->nullable()) {

Review Comment:
   Perhaps make a helper function for this operation and refactor?



##########
cpp/src/parquet/arrow/reader_internal.cc:
##########
@@ -409,22 +441,36 @@ Status TransferDate64(RecordReader* reader, MemoryPool* pool,
 
 Status TransferDictionary(RecordReader* reader,
                           const std::shared_ptr<DataType>& logical_value_type,
-                          std::shared_ptr<ChunkedArray>* out) {
+                          bool nullable, std::shared_ptr<ChunkedArray>* out) {
   auto dict_reader = dynamic_cast<DictionaryRecordReader*>(reader);
   DCHECK(dict_reader);
   *out = dict_reader->GetResult();
   if (!logical_value_type->Equals(*(*out)->type())) {
     ARROW_ASSIGN_OR_RAISE(*out, (*out)->View(logical_value_type));
   }
+  if (!nullable) {
+    // Reconstruct each chunk without nulls.

Review Comment:
   Is this necessary for correctness or is it just an optimization of eliding the null buffer?



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