There exists a ParquetRecordWriter proc macro in parquet_derive, but ParquetRecordReader is missing

[Joseph-Rance]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Reading parquet files into slices of structs can take quite a lot of code. There exists a parquet_derive::ParquetRecordWriter derive macro to write from a slice of structs to a parquet file, but there is no equivalent parquet_derive::ParquetRecordReader macro.

Describe the solution you'd like

A parquet_derive::ParquetRecordReader macro that does the same as parquet_derive::ParquetRecordWriter but for reading.

There already exists a parquet::record::RecordWriter trait:

arrow-rs/parquet/src/record/record_writer.rs

Lines 23 to 31 in 587250c

	pub trait RecordWriter<T> {
	fn write_to_row_group<W: std::io::Write + Send>(
	&self,
	row_group_writer: &mut SerializedRowGroupWriter<W>,
	) -> Result<(), ParquetError>;
	/// Generated schema
	fn schema(&self) -> Result<TypePtr, ParquetError>;
	}

I would like there to be a similar parquet::record::RecordReader trait such as:

pub trait RecordReader<T> {
    fn read_from_row_group(
        &mut self,
        row_group_reader: &mut dyn RowGroupReader,
        max_records: usize,
      ) -> Result<(), ParquetError>;
}

There also exists a parquet_derive::ParquetRecordWriter proc macro to implement this trait for slices of structs:

arrow-rs/parquet_derive/src/lib.rs

Lines 77 to 78 in 587250c

	#[proc_macro_derive(ParquetRecordWriter)]
	pub fn parquet_record_writer(input: proc_macro::TokenStream) -> proc_macro::TokenStream {

Generates code to implement trait here:

arrow-rs/parquet_derive/src/lib.rs

Line 98 in 587250c

impl #generics ::parquet::record::RecordWriter<#derived_for #generics> for &[#derived_for #generics] {

So I would again like there to be a similar parquet_derive::ParquetRecordReader that implements something like:

impl #generics ::parquet::record::RecordReader<#derived_for #generics> for &mut [#derived_for #generics] {

Describe alternatives you've considered

The alternative is for the user to write this code by hand. However, for large structs a macro is necessary and then quickly becomes quite a lot of code ontop of the existing parquet library.

Additional context

I have already implemented a possible solution which I will make a PR for.

[tustvold]

label_issue.py automatically added labels {'parquet'} from #4773

[tustvold]

label_issue.py automatically added labels {'parquet-derive'} from #4773