From 7cab9b6be2d1e038d7cf9ec5cf64223b0e38f0e0 Mon Sep 17 00:00:00 2001
From: Jefffrey <jeffrey.vo.australia@gmail.com>
Date: Mon, 29 Jun 2026 11:38:43 +0900
Subject: [PATCH] fix: read `Dict(FixedSizeBinary)` from parquet without dict
 encoding

---
 parquet/src/arrow/arrow_writer/mod.rs         | 18 ++++++------------
 parquet/src/arrow/buffer/dictionary_buffer.rs | 12 +++++++++++-
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/parquet/src/arrow/arrow_writer/mod.rs b/parquet/src/arrow/arrow_writer/mod.rs
index 063d5abcf1c4..271afedd08a5 100644
--- a/parquet/src/arrow/arrow_writer/mod.rs
+++ b/parquet/src/arrow/arrow_writer/mod.rs
@@ -2933,16 +2933,6 @@ mod tests {
             K::Native: FromPrimitive + ToPrimitive + TryFrom<u8>,
             <<K as arrow_array::ArrowPrimitiveType>::Native as TryFrom<u8>>::Error: std::fmt::Debug,
         {
-            let field = Field::new(
-                "a",
-                DataType::Dictionary(
-                    Box::new(K::DATA_TYPE),
-                    Box::new(DataType::FixedSizeBinary(4)),
-                ),
-                false,
-            );
-            let schema = Schema::new(vec![field]);
-
             let keys: Vec<K::Native> = vec![
                 K::Native::try_from(0u8).unwrap(),
                 K::Native::try_from(0u8).unwrap(),
@@ -2954,8 +2944,12 @@ mod tests {
             )
             .unwrap();
 
-            let data = DictionaryArray::<K>::new(keys, Arc::new(values));
-            let batch = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(data)]).unwrap();
+            let data = Arc::new(DictionaryArray::<K>::new(keys, Arc::new(values))) as ArrayRef;
+            one_column_roundtrip(Arc::clone(&data), true);
+
+            let field = Field::new("a", data.data_type().clone(), false);
+            let schema = Schema::new(vec![field]);
+            let batch = RecordBatch::try_new(Arc::new(schema), vec![data]).unwrap();
             roundtrip(batch, None);
         }
 
diff --git a/parquet/src/arrow/buffer/dictionary_buffer.rs b/parquet/src/arrow/buffer/dictionary_buffer.rs
index abf76530296c..ba9390746bed 100644
--- a/parquet/src/arrow/buffer/dictionary_buffer.rs
+++ b/parquet/src/arrow/buffer/dictionary_buffer.rs
@@ -185,8 +185,18 @@ impl<K: ArrowNativeType + Ord, V: OffsetSizeTrait> DictionaryBuffer<K, V> {
                     ArrowType::Dictionary(k, v) => (k, v.as_ref().clone()),
                     _ => unreachable!(),
                 };
+                let array = if let ArrowType::FixedSizeBinary(size) = value_type {
+                    let array = values.into_array(null_buffer, ArrowType::Binary);
+                    let array = array.as_binary::<i32>();
+                    Arc::new(FixedSizeBinaryArray::new(
+                        size,
+                        array.values().clone(),
+                        array.nulls().cloned(),
+                    )) as _
+                } else {
+                    values.into_array(null_buffer, value_type)
+                };
 
-                let array = values.into_array(null_buffer, value_type);
                 pack_values(key_type, &array)
             }
         }