ARROW-14658: [C++] Add basic support for nested field refs in scanning

cpp/src/arrow/compute/exec/plan_test.cc

@@ -793,6 +793,73 @@ TEST(ExecPlanExecution, SourceGroupedSum) {
   }
 }
 
+TEST(ExecPlanExecution, NestedSourceFilter) {
+  for (bool parallel : {false, true}) {
+    SCOPED_TRACE(parallel ? "parallel/merged" : "serial");
+
+    auto input = MakeNestedBatches();
+    auto empty = ExecBatchFromJSON({input.schema->field(0)->type()}, R"([])");
+    auto expected = ExecBatchFromJSON({input.schema->field(0)->type()}, R"([
+      [{"i32": 5, "bool": null}],
+      [{"i32": 6, "bool": false}],
+      [{"i32": 7, "bool": false}]
+])");
+
+    ASSERT_OK_AND_ASSIGN(auto plan, ExecPlan::Make());
+    AsyncGenerator<util::optional<ExecBatch>> sink_gen;
+
+    ASSERT_OK(Declaration::Sequence(
+                  {
+                      {"source", SourceNodeOptions{input.schema,
+                                                   input.gen(parallel, /*slow=*/false)}},
+                      {"filter", FilterNodeOptions{greater_equal(
+                                     field_ref(FieldRef("struct", "i32")), literal(5))}},
+                      {"sink", SinkNodeOptions{&sink_gen}},
+                  })
+                  .AddToPlan(plan.get()));
+
+    ASSERT_THAT(StartAndCollect(plan.get(), sink_gen),
+                Finishes(ResultWith(UnorderedElementsAreArray({empty, expected}))));
+  }
+}
+
+TEST(ExecPlanExecution, NestedSourceProjectGroupedSum) {
+  for (bool parallel : {false, true}) {
+    SCOPED_TRACE(parallel ? "parallel/merged" : "serial");
+
+    auto input = MakeNestedBatches();
+    auto expected = ExecBatchFromJSON({int64(), boolean()}, R"([
+      [null, true],
+      [17, false],
+      [5, null]
+])");
+
+    ASSERT_OK_AND_ASSIGN(auto plan, ExecPlan::Make());
+    AsyncGenerator<util::optional<ExecBatch>> sink_gen;
+
+    ASSERT_OK(
+        Declaration::Sequence(
+            {
+                {"source",
+                 SourceNodeOptions{input.schema, input.gen(parallel, /*slow=*/false)}},
+                {"project", ProjectNodeOptions{{
+                                                   field_ref(FieldRef("struct", "i32")),
+                                                   field_ref(FieldRef("struct", "bool")),
+                                               },
+                                               {"i32", "bool"}}},
+                {"aggregate", AggregateNodeOptions{/*aggregates=*/{{"hash_sum", nullptr}},
+                                                   /*targets=*/{"i32"},
+                                                   /*names=*/{"sum(i32)"},
+                                                   /*keys=*/{"bool"}}},
+                {"sink", SinkNodeOptions{&sink_gen}},
+            })
+            .AddToPlan(plan.get()));
+
+    ASSERT_THAT(StartAndCollect(plan.get(), sink_gen),
+                Finishes(ResultWith(UnorderedElementsAreArray({expected}))));
+  }
+}
+
 TEST(ExecPlanExecution, SourceFilterProjectGroupedSumFilter) {
   for (bool parallel : {false, true}) {
     SCOPED_TRACE(parallel ? "parallel/merged" : "serial");

cpp/src/arrow/compute/exec/test_util.cc

@@ -190,6 +190,20 @@ BatchesWithSchema MakeBasicBatches() {
   return out;
 }
 
+BatchesWithSchema MakeNestedBatches() {
+  auto ty = struct_({field("i32", int32()), field("bool", boolean())});
+  BatchesWithSchema out;
+  out.batches = {
+      ExecBatchFromJSON(
+          {ty},
+          R"([[{"i32": null, "bool": true}], [{"i32": 4, "bool": false}], [null]])"),
+      ExecBatchFromJSON(
+          {ty},
+          R"([[{"i32": 5, "bool": null}], [{"i32": 6, "bool": false}], [{"i32": 7, "bool": false}]])")};
+  out.schema = schema({field("struct", ty)});
+  return out;
+}
+
 BatchesWithSchema MakeRandomBatches(const std::shared_ptr<Schema>& schema,
                                     int num_batches, int batch_size) {
   BatchesWithSchema out;

cpp/src/arrow/compute/exec/test_util.h

@@ -87,6 +87,9 @@ Future<std::vector<ExecBatch>> StartAndCollect(
 ARROW_TESTING_EXPORT
 BatchesWithSchema MakeBasicBatches();
 
+ARROW_TESTING_EXPORT
+BatchesWithSchema MakeNestedBatches();
+
 ARROW_TESTING_EXPORT
 BatchesWithSchema MakeRandomBatches(const std::shared_ptr<Schema>& schema,
                                     int num_batches = 10, int batch_size = 4);

cpp/src/arrow/dataset/file_csv.cc

@@ -116,9 +116,28 @@ static inline Result<csv::ConvertOptions> GetConvertOptions(
 
   if (!scan_options) return convert_options;
 
-  auto materialized = scan_options->MaterializedFields();
-  std::unordered_set<std::string> materialized_fields(materialized.begin(),
-                                                      materialized.end());
+  auto field_refs = scan_options->MaterializedFields();
+  std::unordered_set<std::string> materialized_fields;
+  materialized_fields.reserve(field_refs.size());
+  // Preprocess field refs. We try to avoid FieldRef::GetFoo here since that's
+  // quadratic (and this is significant overhead with 1000+ columns)
+  for (const auto& ref : field_refs) {
+    if (const std::string* name = ref.name()) {
+      // Common case
+      materialized_fields.emplace(*name);
+      continue;
+    }
+    // Currently CSV reader doesn't support reading any nested types, so this
+    // path shouldn't be hit. However, implement it in the same way as IPC/ORC:
+    // load the entire top-level field if a nested field is selected.
+    ARROW_ASSIGN_OR_RAISE(auto field, ref.GetOneOrNone(*scan_options->dataset_schema));
+    if (column_names.find(field->name()) == column_names.end()) continue;
+    // Only read the requested columns
+    convert_options.include_columns.push_back(field->name());
+    // Properly set conversion types
+    convert_options.column_types[field->name()] = field->type();
+  }
+
   for (auto field : scan_options->dataset_schema->fields()) {
     if (materialized_fields.find(field->name()) == materialized_fields.end()) continue;
     // Ignore virtual columns.

cpp/src/arrow/dataset/file_csv_test.cc

@@ -384,13 +384,20 @@ class TestCsvFileFormatScan : public FileFormatScanMixin<CsvFormatHelper> {};
 
 TEST_P(TestCsvFileFormatScan, ScanRecordBatchReader) { TestScan(); }
 TEST_P(TestCsvFileFormatScan, ScanBatchSize) { TestScanBatchSize(); }
-TEST_P(TestCsvFileFormatScan, ScanRecordBatchReaderWithVirtualColumn) {
-  TestScanWithVirtualColumn();
-}
 TEST_P(TestCsvFileFormatScan, ScanRecordBatchReaderProjected) { TestScanProjected(); }
+// NOTE(ARROW-14658): TestScanProjectedNested is ignored since CSV
+// doesn't have any nested types for us to work with
 TEST_P(TestCsvFileFormatScan, ScanRecordBatchReaderProjectedMissingCols) {
   TestScanProjectedMissingCols();
 }
+TEST_P(TestCsvFileFormatScan, ScanRecordBatchReaderWithVirtualColumn) {
+  TestScanWithVirtualColumn();
+}
+// The CSV reader rejects duplicate columns, so skip
+// ScanRecordBatchReaderWithDuplicateColumn
+TEST_P(TestCsvFileFormatScan, ScanRecordBatchReaderWithDuplicateColumnError) {
+  TestScanWithDuplicateColumnError();
+}
 
 INSTANTIATE_TEST_SUITE_P(TestScan, TestCsvFileFormatScan,
                          ::testing::ValuesIn(TestFormatParams::Values()),

cpp/src/arrow/dataset/file_ipc.cc

@@ -75,10 +75,10 @@ static inline Future<std::shared_ptr<ipc::RecordBatchFileReader>> OpenReaderAsyn
 }
 
 static inline Result<std::vector<int>> GetIncludedFields(
-    const Schema& schema, const std::vector<std::string>& materialized_fields) {
+    const Schema& schema, const std::vector<FieldRef>& materialized_fields) {
   std::vector<int> included_fields;
 
-  for (FieldRef ref : materialized_fields) {
+  for (const auto& ref : materialized_fields) {
     ARROW_ASSIGN_OR_RAISE(auto match, ref.FindOneOrNone(schema));
     if (match.indices().empty()) continue;
 

cpp/src/arrow/dataset/file_ipc_test.cc

@@ -135,13 +135,22 @@ class TestIpcFileFormatScan : public FileFormatScanMixin<IpcFormatHelper> {};
 
 TEST_P(TestIpcFileFormatScan, ScanRecordBatchReader) { TestScan(); }
 TEST_P(TestIpcFileFormatScan, ScanBatchSize) { TestScanBatchSize(); }
-TEST_P(TestIpcFileFormatScan, ScanRecordBatchReaderWithVirtualColumn) {
-  TestScanWithVirtualColumn();
-}
 TEST_P(TestIpcFileFormatScan, ScanRecordBatchReaderProjected) { TestScanProjected(); }
+TEST_P(TestIpcFileFormatScan, ScanRecordBatchReaderProjectedNested) {
+  TestScanProjectedNested();
+}
 TEST_P(TestIpcFileFormatScan, ScanRecordBatchReaderProjectedMissingCols) {
   TestScanProjectedMissingCols();
 }
+TEST_P(TestIpcFileFormatScan, ScanRecordBatchReaderWithVirtualColumn) {
+  TestScanWithVirtualColumn();
+}
+TEST_P(TestIpcFileFormatScan, ScanRecordBatchReaderWithDuplicateColumn) {
+  TestScanWithDuplicateColumn();
+}
+TEST_P(TestIpcFileFormatScan, ScanRecordBatchReaderWithDuplicateColumnError) {
+  TestScanWithDuplicateColumnError();
+}
 TEST_P(TestIpcFileFormatScan, FragmentScanOptions) {
   auto reader = GetRecordBatchReader(
       // ARROW-12077: on Windows/mimalloc/release, nullable list column leads to crash

cpp/src/arrow/dataset/file_orc.cc

@@ -79,12 +79,11 @@ class OrcScanTask {
         // filter out virtual columns
         std::vector<std::string> included_fields;
         ARROW_ASSIGN_OR_RAISE(auto schema, reader->ReadSchema());
-        for (auto name : materialized_fields) {
-          FieldRef ref(name);
+        for (const auto& ref : materialized_fields) {
           ARROW_ASSIGN_OR_RAISE(auto match, ref.FindOneOrNone(*schema));
           if (match.indices().empty()) continue;
 
-          included_fields.push_back(name);
+          included_fields.push_back(schema->field(match.indices()[0])->name());
         }
 
         return RecordBatchIterator(

cpp/src/arrow/dataset/file_orc_test.cc

@@ -69,13 +69,25 @@ TEST_F(TestOrcFileFormat, CountRows) { TestCountRows(); }
 class TestOrcFileFormatScan : public FileFormatScanMixin<OrcFormatHelper> {};
 
 TEST_P(TestOrcFileFormatScan, ScanRecordBatchReader) { TestScan(); }
-TEST_P(TestOrcFileFormatScan, ScanRecordBatchReaderWithVirtualColumn) {
-  TestScanWithVirtualColumn();
+TEST_P(TestOrcFileFormatScan, ScanBatchSize) {
+  // TODO(ARROW-14153): TestScanBatchSize();
 }
 TEST_P(TestOrcFileFormatScan, ScanRecordBatchReaderProjected) { TestScanProjected(); }
+TEST_P(TestOrcFileFormatScan, ScanRecordBatchReaderProjectedNested) {
+  TestScanProjectedNested();
+}
 TEST_P(TestOrcFileFormatScan, ScanRecordBatchReaderProjectedMissingCols) {
   TestScanProjectedMissingCols();
 }
+TEST_P(TestOrcFileFormatScan, ScanRecordBatchReaderWithVirtualColumn) {
+  TestScanWithVirtualColumn();
+}
+TEST_P(TestOrcFileFormatScan, ScanRecordBatchReaderWithDuplicateColumn) {
+  TestScanWithDuplicateColumn();
+}
+TEST_P(TestOrcFileFormatScan, ScanRecordBatchReaderWithDuplicateColumnError) {
+  TestScanWithDuplicateColumnError();
+}
 INSTANTIATE_TEST_SUITE_P(TestScan, TestOrcFileFormatScan,
                          ::testing::ValuesIn(TestFormatParams::Values()),
                          TestFormatParams::ToTestNameString);

cpp/src/arrow/dataset/file_parquet.cc

@@ -155,30 +155,112 @@ void AddColumnIndices(const SchemaField& schema_field,
   }
 }
 
-// Compute the column projection out of an optional arrow::Schema
-std::vector<int> InferColumnProjection(const parquet::arrow::FileReader& reader,
-                                       const ScanOptions& options) {
+Status ResolveOneFieldRef(
+    const SchemaManifest& manifest, const FieldRef& field_ref,
+    const std::unordered_map<std::string, const SchemaField*>& field_lookup,
+    const std::unordered_set<std::string>& duplicate_fields,
+    std::vector<int>* columns_selection) {
+  if (const std::string* name = field_ref.name()) {
+    auto it = field_lookup.find(*name);
+    if (it != field_lookup.end()) {
+      AddColumnIndices(*it->second, columns_selection);
+    } else if (duplicate_fields.find(*name) != duplicate_fields.end()) {
+      // We shouldn't generally get here because SetProjection will reject such references
+      return Status::Invalid("Ambiguous reference to column '", *name,
+                             "' which occurs more than once");
+    }
+    // "Virtual" column: field is not in file but is in the ScanOptions.
+    // Ignore it here, as projection will pad the batch with a null column.
+    return Status::OK();
+  }
+
+  const SchemaField* toplevel = nullptr;
+  const SchemaField* field = nullptr;
+  if (const std::vector<FieldRef>* refs = field_ref.nested_refs()) {
+    // Only supports a sequence of names
+    for (const auto& ref : *refs) {
+      if (const std::string* name = ref.name()) {
+        if (!field) {
+          // First lookup, top-level field
+          auto it = field_lookup.find(*name);
+          if (it != field_lookup.end()) {
+            field = it->second;
+            toplevel = field;
+          } else if (duplicate_fields.find(*name) != duplicate_fields.end()) {
+            return Status::Invalid("Ambiguous reference to column '", *name,
+                                   "' which occurs more than once");
+          } else {
+            // Virtual column
+            return Status::OK();
+          }
+        } else {
+          const SchemaField* result = nullptr;
+          for (const auto& child : field->children) {
+            if (child.field->name() == *name) {
+              if (!result) {
+                result = &child;
+              } else {
+                return Status::Invalid("Ambiguous nested reference to column '", *name,
+                                       "' which occurs more than once in field ",
+                                       field->field->ToString());
+              }
+            }
+          }
+          if (!result) {
+            // Virtual column
+            return Status::OK();
+          }
+          field = result;
+        }
+        continue;
+      }
+      return Status::NotImplemented("Inferring column projection from FieldRef ",
+                                    field_ref.ToString());
+    }
+  } else {
+    return Status::NotImplemented("Inferring column projection from FieldRef ",
+                                  field_ref.ToString());
+  }
+
+  if (field) {
+    // TODO(ARROW-1888): support fine-grained column projection. We should be
+    // able to materialize only the child fields requested, and not the entire
+    // top-level field.
+    // Right now, if enabled, projection/filtering will fail when they cast the
+    // physical schema to the dataset schema.
+    AddColumnIndices(*toplevel, columns_selection);
+  }
+  return Status::OK();
+}
+
+// Compute the column projection based on the scan options
+Result<std::vector<int>> InferColumnProjection(const parquet::arrow::FileReader& reader,
+                                               const ScanOptions& options) {
   auto manifest = reader.manifest();
   // Checks if the field is needed in either the projection or the filter.
-  auto field_names = options.MaterializedFields();
-  std::unordered_set<std::string> materialized_fields{field_names.cbegin(),
-                                                      field_names.cend()};
-  auto should_materialize_column = [&materialized_fields](const std::string& f) {
-    return materialized_fields.find(f) != materialized_fields.end();
-  };
-
-  std::vector<int> columns_selection;
-  // Note that the loop is using the file's schema to iterate instead of the
-  // materialized fields of the ScanOptions. This ensures that missing
-  // fields in the file (but present in the ScanOptions) will be ignored. The
-  // scanner's projector will take care of padding the column with the proper
-  // values.
+  auto field_refs = options.MaterializedFields();
+
+  // Build a lookup table from top level field name to field metadata.
+  // This is to avoid quadratic-time mapping of projected fields to
+  // column indices, in the common case of selecting top level
+  // columns. For nested fields, we will pay the cost of a linear scan
+  // assuming for now that this is relatively rare, but this can be
+  // optimized. (Also, we don't want to pay the cost of building all
+  // the lookup tables up front if they're rarely used.)
+  std::unordered_map<std::string, const SchemaField*> field_lookup;
+  std::unordered_set<std::string> duplicate_fields;
   for (const auto& schema_field : manifest.schema_fields) {
-    if (should_materialize_column(schema_field.field->name())) {
-      AddColumnIndices(schema_field, &columns_selection);
+    const auto it = field_lookup.emplace(schema_field.field->name(), &schema_field);
+    if (!it.second) {
+      duplicate_fields.emplace(schema_field.field->name());
     }
   }
 
+  std::vector<int> columns_selection;
+  for (const auto& ref : field_refs) {
+    RETURN_NOT_OK(ResolveOneFieldRef(manifest, ref, field_lookup, duplicate_fields,
+                                     &columns_selection));
+  }
   return columns_selection;
 }
 
@@ -351,7 +433,8 @@ Result<RecordBatchGenerator> ParquetFileFormat::ScanBatchesAsync(
                             parquet_fragment->FilterRowGroups(options->filter));
       if (row_groups.empty()) return MakeEmptyGenerator<std::shared_ptr<RecordBatch>>();
     }
-    auto column_projection = InferColumnProjection(*reader, *options);
+    ARROW_ASSIGN_OR_RAISE(auto column_projection,
+                          InferColumnProjection(*reader, *options));
     ARROW_ASSIGN_OR_RAISE(
         auto parquet_scan_options,
         GetFragmentScanOptions<ParquetFragmentScanOptions>(