[GitHub] [arrow-datafusion] Dandandan commented on a change in pull request #2000: Fixed parquet path partitioning when only selecting partitioned columns

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

Dandandan commented on a change in pull request #2000:
URL: https://github.com/apache/arrow-datafusion/pull/2000#discussion_r833691608



##########
File path: datafusion/src/physical_plan/file_format/mod.rs
##########
@@ -293,6 +293,34 @@ impl PartitionColumnProjector {
         }
     }
 
+    // Creates a RecordBatch with values from the partition_values. Used when no non-partition values are read
+    fn project_empty(
+        &mut self,
+        batch_size: usize,
+        partition_values: &[ScalarValue],
+    ) -> ArrowResult<RecordBatch> {
+        let expected_cols = self.projected_schema.fields().len();
+        if expected_cols != self.projected_partition_indexes.len() {
+            return Err(ArrowError::SchemaError(format!(
+                "Unexepected number of partition values, expected {} but got {}",
+                expected_cols,
+                partition_values.len()
+            )));
+        }
+        let mut cols = Vec::with_capacity(partition_values.len());

Review comment:
       Small style suggestion: I think we can rewrite this to use `.collect()` on an iterator.




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