[GitHub] [arrow] bkietz commented on a change in pull request #7704: ARROW-9297: [C++][Parquet] Support chunked row groups in RowGroupRecordBatchReader

[GitBox]

bkietz commented on a change in pull request #7704:
URL: https://github.com/apache/arrow/pull/7704#discussion_r453241420



##########
File path: cpp/src/parquet/arrow/arrow_schema_test.cc
##########
@@ -644,6 +649,78 @@ TEST_F(TestConvertParquetSchema, 
ParquetRepeatedNestedSchema) {
   ASSERT_NO_FATAL_FAILURE(CheckFlatSchema(arrow_schema));
 }
 
+TEST_F(TestConvertParquetSchema, ColumnSubselection) {
+  std::vector<NodePtr> parquet_fields;
+  std::vector<std::shared_ptr<Field>> arrow_fields;
+  {
+    //   optional int32 leaf1;
+    //   repeated group outerGroup {
+    //     optional int32 leaf2;
+    //     repeated group innerGroup {
+    //       optional int32 leaf3;
+    //     }
+    //   }
+    parquet_fields.push_back(
+        PrimitiveNode::Make("leaf1", Repetition::OPTIONAL, 
ParquetType::INT32));
+    parquet_fields.push_back(GroupNode::Make(
+        "outerGroup", Repetition::REPEATED,
+        {PrimitiveNode::Make("leaf2", Repetition::OPTIONAL, 
ParquetType::INT32),
+         GroupNode::Make(
+             "innerGroup", Repetition::REPEATED,
+             {PrimitiveNode::Make("leaf3", Repetition::OPTIONAL, 
ParquetType::INT32)})}));
+
+    auto inner_group_fields = {::arrow::field("leaf3", INT32, true)};

Review comment:
       Re JSON util: I'm not convinced that would be significantly more concise 
than our (de-facto) DSL with `schema`, `field`, and friends. Here's what I'm 
thinking of:
   
   ```json
   {
     "leaf1": "int32",
     "outerGroup": {
       "nested": "struct",
       "fields": [{
         "leaf2": "int32",
         "innerGroup": {
           "nested": "list not null",
           "fields": [{
             "inner-erGroup": {
               "nested": "struct not null",
               "fields": {
                 "leaf3": "int32"
               }
             }
           }]
         }
       }]
     }
   }
   ```
   
   vs
   
   ```c++
   schema({
     field("leaf1", int32()),
     field("outerGroup", struct_({
       field("leaf2", int32()),
       field("innerGroup", list(
         field("inner-erGroup", struct_({
           field("leaf3", int32())
         }), false)
       ), false),
     }))
   })
   ```




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