westonpace commented on code in PR #13782:
URL: https://github.com/apache/arrow/pull/13782#discussion_r980545312
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cpp/src/arrow/dataset/dataset.h:
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@@ -37,11 +38,107 @@ namespace dataset {
using RecordBatchGenerator =
std::function<Future<std::shared_ptr<RecordBatch>>()>;
+/// \brief Description of a column to scan
+struct FragmentSelectionColumn {
Review Comment:
Added
##########
cpp/src/arrow/dataset/dataset.h:
##########
@@ -37,11 +38,107 @@ namespace dataset {
using RecordBatchGenerator =
std::function<Future<std::shared_ptr<RecordBatch>>()>;
+/// \brief Description of a column to scan
+struct FragmentSelectionColumn {
+ /// \brief The path to the column to load
+ FieldPath column_reference;
+ /// \brief The requested type of the column
+ ///
+ /// A format may choose to ignore this field completely. For example, when
+ /// reading from IPC the reader can just return the column in the data type
+ /// that is stored on disk. In this case the scan node will cast the column
+ /// to the appropriate type later.
+ ///
+ /// However, some formats may be capable of casting on the fly. For example,
+ /// when reading from CSV, if we know the target type of the column, we can
+ /// convert from string to the target type as we read.
+ DataType* requested_type;
+};
+/// \brief Instructions for scanning a particular fragment
+///
+/// The fragment scan request is dervied from ScanV2Options. The main
+/// difference is that the scan options are based on the dataset schema
+/// while the fragment request is based on the fragment schema.
+struct FragmentScanRequest {
Review Comment:
Added (here and elsewhere)
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