[GitHub] [arrow] nevi-me commented on a change in pull request #8291: ARROW-8426: [Rust] [Parquet] Add support for writing dictionary types

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

nevi-me commented on a change in pull request #8291:
URL: https://github.com/apache/arrow/pull/8291#discussion_r499097627



##########
File path: rust/arrow/src/ipc/convert.rs
##########
@@ -609,10 +621,45 @@ pub(crate) fn get_fb_field_type<'a: 'b, 'b>(
                 children: Some(fbb.create_vector(&children[..])),
             }
         }
+        Dictionary(_, value_type) => {
+            // In this library, the dictionary "type" is a logical construct. Here we
+            // pass through to the value type, as we've already captured the index
+            // type in the DictionaryEncoding metadata in the parent field
+            get_fb_field_type(value_type, fbb)
+        }
         t => unimplemented!("Type {:?} not supported", t),
     }
 }
 
+/// Create an IPC dictionary encoding
+pub(crate) fn get_fb_dictionary<'a: 'b, 'b>(
+    index_type: &DataType,
+    dict_id: i64,
+    dict_is_ordered: bool,
+    fbb: &mut FlatBufferBuilder<'a>,
+) -> WIPOffset<ipc::DictionaryEncoding<'b>> {
+    // We assume that the dictionary index type (as an integer) has already been
+    // validated elsewhere, and can safely assume we are dealing with signed
+    // integers
+    let mut index_builder = ipc::IntBuilder::new(fbb);
+    index_builder.add_is_signed(true);

Review comment:
       @carols10cents we can address this in future, I'm merging this




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