[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #3907: Add serde for plans with tables from `TableProviderFactory`s

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

alamb commented on code in PR #3907:
URL: https://github.com/apache/arrow-datafusion/pull/3907#discussion_r1000956863


##########
datafusion/proto/src/logical_plan.rs:
##########
@@ -760,55 +804,21 @@ impl AsLogicalPlan for LogicalPlanNode {
                     .collect::<Result<Vec<_>, _>>()?;
 
                 if let Some(listing_table) = source.downcast_ref::<ListingTable>() {
-                    let any = listing_table.options().format.as_any();
-                    let file_format_type = if let Some(parquet) =
-                        any.downcast_ref::<ParquetFormat>()
-                    {
-                        FileFormatType::Parquet(protobuf::ParquetFormat {
-                            enable_pruning: parquet.enable_pruning(),
-                        })
-                    } else if let Some(csv) = any.downcast_ref::<CsvFormat>() {
-                        FileFormatType::Csv(protobuf::CsvFormat {
-                            delimiter: byte_to_string(csv.delimiter())?,
-                            has_header: csv.has_header(),
-                        })
-                    } else if any.is::<AvroFormat>() {
-                        FileFormatType::Avro(protobuf::AvroFormat {})
-                    } else {
-                        return Err(proto_error(format!(
-                            "Error converting file format, {:?} is invalid as a datafusion foramt.",
-                            listing_table.options().format
-                        )));
-                    };
-                    Ok(protobuf::LogicalPlanNode {
-                        logical_plan_type: Some(LogicalPlanType::ListingScan(
-                            protobuf::ListingTableScanNode {
-                                file_format_type: Some(file_format_type),
-                                table_name: table_name.to_owned(),
-                                collect_stat: listing_table.options().collect_stat,
-                                file_extension: listing_table
-                                    .options()
-                                    .file_extension
-                                    .clone(),
-                                table_partition_cols: listing_table
-                                    .options()
-                                    .table_partition_cols
-                                    .clone(),
-                                paths: listing_table
-                                    .table_paths()
-                                    .iter()
-                                    .map(|x| x.to_string())
-                                    .collect(),
-                                schema: Some(schema),
-                                projection,
-                                filters,
-                                target_partitions: listing_table
-                                    .options()
-                                    .target_partitions
-                                    as u32,
-                            },
-                        )),
-                    })
+                    Self::serialize_listing_table(
+                        table_name,
+                        projection,
+                        schema,
+                        filters,
+                        listing_table,
+                    )
+                } else if let Some(custom_table) = source.downcast_ref::<CustomTable>() {

Review Comment:
   So this seems to be the key issue -- if `source` isn't some type that DataFusion knows about it can't do a useful job serializing it.
   
   I don't fully understand how a `CustomTable` struct will help -- at some point the client code needs to get the concrete  `TableProvider`, not a `CustomTable`.
   
   I think there was a similar issue serializing "extensions" for which @thinkharderdev  added 
   
   ```rust
   pub trait LogicalExtensionCodec: Debug + Send + Sync {
   ```
   
   I wonder if we can follow the same model here , something like add `LogicalExtensionCodec::try_encoded_table_provider` and `LogicalExtensionCodec::try_decode_table_provider`
   
   
   ```rust
   if let Some(listing_table) = source.downcast_ref::<ListingTable>() {
     // ...
   } else {
     // delegate to provided extension codec:
     extension_codec.try_encode_table_provider(
                   table_name,
                   source,
                   filters,
                   projection,
     ); 
   } 
   ```



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