[GitHub] [arrow-rs] viirya commented on a diff in pull request #1560: Support empty projection in ParquetRecordBatchReader

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

viirya commented on code in PR #1560:
URL: https://github.com/apache/arrow-rs/pull/1560#discussion_r849739790


##########
parquet/src/arrow/array_reader/empty_array.rs:
##########
@@ -0,0 +1,75 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use crate::arrow::array_reader::ArrayReader;
+use crate::errors::Result;
+use arrow::array::{ArrayDataBuilder, ArrayRef, StructArray};
+use arrow::datatypes::DataType as ArrowType;
+use std::any::Any;
+use std::sync::Arc;
+
+/// Returns an [`ArrayReader`] that yields [`StructArray`] with no columns
+/// but with row counts that correspond to the amount of data in the file
+///
+/// This is useful for when projection eliminates all columns within a collection
+pub fn make_empty_array_reader(row_count: usize) -> Box<dyn ArrayReader> {
+    Box::new(EmptyArrayReader::new(row_count))
+}
+
+struct EmptyArrayReader {
+    data_type: ArrowType,

Review Comment:
   `data_type` seems not necessary to keep here, it is always `ArrowType::Struct(vec![])`.



-- 
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

To unsubscribe, e-mail: github-unsubscribe@arrow.apache.org

For queries about this service, please contact Infrastructure at:
users@infra.apache.org