[arrow] branch main updated: PARQUET-2250:[C++][Parquet] Expose column descriptor through RecordReader (#34318)

[westonpace]

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The following commit(s) were added to refs/heads/main by this push:
     new 50fb5b0df8 PARQUET-2250:[C++][Parquet] Expose column descriptor 
through RecordReader (#34318)
50fb5b0df8 is described below

commit 50fb5b0df84a3ccaa665965e36a6e757d1af98f1
Author: Fatemah Panahi <fatem...@users.noreply.github.com>
AuthorDate: Thu Mar 2 16:43:37 2023 -0800

    PARQUET-2250:[C++][Parquet] Expose column descriptor through RecordReader 
(#34318)
    
    This change exposes the column descriptor through the RecordReader.
    
    Lead-authored-by: Fatemah Panahi <pan...@google.com>
    Co-authored-by: Fatemah Panahi <fatem...@users.noreply.github.com>
    Signed-off-by: Weston Pace <weston.p...@gmail.com>
---
 cpp/src/parquet/column_reader.cc      | 2 ++
 cpp/src/parquet/column_reader.h       | 3 +++
 cpp/src/parquet/column_reader_test.cc | 3 +++
 3 files changed, 8 insertions(+)

diff --git a/cpp/src/parquet/column_reader.cc b/cpp/src/parquet/column_reader.cc
index f19079b902..7e650596a6 100644
--- a/cpp/src/parquet/column_reader.cc
+++ b/cpp/src/parquet/column_reader.cc
@@ -1813,6 +1813,8 @@ class TypedRecordReader : public 
TypedColumnReaderImpl<DType>,
 
   bool HasMoreData() const override { return this->pager_ != nullptr; }
 
+  const ColumnDescriptor* descr() const override { return this->descr_; }
+
   // Dictionary decoders must be reset when advancing row groups
   void ResetDecoders() { this->decoders_.clear(); }
 
diff --git a/cpp/src/parquet/column_reader.h b/cpp/src/parquet/column_reader.h
index b5f96f8fc4..a9f6e217b1 100644
--- a/cpp/src/parquet/column_reader.h
+++ b/cpp/src/parquet/column_reader.h
@@ -351,6 +351,9 @@ class PARQUET_EXPORT RecordReader {
   /// \param[in] reader obtained from RowGroupReader::GetColumnPageReader
   virtual void SetPageReader(std::unique_ptr<PageReader> reader) = 0;
 
+  /// \brief Returns the underlying column reader's descriptor.
+  virtual const ColumnDescriptor* descr() const = 0;
+
   virtual void DebugPrintState() = 0;
 
   /// \brief Decoded definition levels
diff --git a/cpp/src/parquet/column_reader_test.cc 
b/cpp/src/parquet/column_reader_test.cc
index 32fb09f21b..a8ce72165a 100644
--- a/cpp/src/parquet/column_reader_test.cc
+++ b/cpp/src/parquet/column_reader_test.cc
@@ -727,6 +727,9 @@ TEST_F(RecordReaderTest, BasicReadRepeatedField) {
   int64_t records_read = record_reader_->ReadRecords(/*num_records=*/0);
   ASSERT_EQ(records_read, 0);
 
+  // Test the descr() accessor.
+  ASSERT_EQ(record_reader_->descr()->max_definition_level(), 1);
+
   // Read [10], null
   records_read = record_reader_->ReadRecords(/*num_records=*/2);
   ASSERT_EQ(records_read, 2);