[GitHub] [arrow-rs] mapleFU commented on a diff in pull request #4326: Add separate row_count and level_count to PageMetadata (#4321)

["mapleFU (via GitHub)" <gi...@apache.org>]

mapleFU commented on code in PR #4326:
URL: https://github.com/apache/arrow-rs/pull/4326#discussion_r1213087653


##########
parquet/src/column/page.rs:
##########
@@ -277,18 +278,27 @@ impl TryFrom<&PageHeader> for PageMetadata {
 
     fn try_from(value: &PageHeader) -> std::result::Result<Self, Self::Error> {
         match value.type_ {
-            crate::format::PageType::DATA_PAGE => Ok(PageMetadata {
-                num_rows: value.data_page_header.as_ref().unwrap().num_values as usize,
-                is_dict: false,
-            }),
+            crate::format::PageType::DATA_PAGE => {
+                let header = value.data_page_header.as_ref().unwrap();
+                Ok(PageMetadata {
+                    num_rows: None,
+                    num_levels: Some(header.num_values as _),

Review Comment:
   I guess when page `max_def_level == 0`, `num_values` doesn't means `num_levels`? 



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