Re: [PR] Add `RecordReader` trait and proc macro to implement it for a struct [arrow-rs]

["Joseph-Rance (via GitHub)" <gi...@apache.org>]

Joseph-Rance commented on code in PR #4773:
URL: https://github.com/apache/arrow-rs/pull/4773#discussion_r1342545617


##########
parquet_derive/README.md:
##########
@@ -77,16 +77,55 @@ writer.close_row_group(row_group).unwrap();
 writer.close().unwrap();
 ```
 
+Example usage of deriving a `RecordReader` for your struct:
+
+```rust
+use parquet::file::{serialized_reader::SerializedFileReader, reader::FileReader};
+use parquet_derive::ParquetRecordReader;
+
+#[derive(ParquetRecordReader)]
+struct ACompleteRecord {
+    pub a_bool: bool,
+    pub a_string: String,
+    pub i16: i16,
+    pub i32: i32,
+    pub u64: u64,
+    pub isize: isize,
+    pub float: f32,
+    pub double: f64,
+    pub now: chrono::NaiveDateTime,
+    pub byte_vec: Vec<u8>,
+}
+
+// Initialize your parquet file
+let reader = SerializedFileReader::new(file).unwrap();
+let mut row_group = reader.get_row_group(0).unwrap();
+
+// create your records to read into
+let mut chunks = vec![ACompleteRecord{ ... }];

Review Comment:
   Where do you want to initialise the structs? If we want to do it at the start of the macro we would need the struct to derive default, which I think might be problematic for some structs. I don't think we can very easily initialise the struct with all the data we have already read because we read them column by column. I can save the columns and then build the structs after the entire file is read but this seems possibly overcomplicated compared to just letting the user initialise the structs.



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