From 88e681baf28bbb691b60c30045ec62d5ef1b8d94 Mon Sep 17 00:00:00 2001
From: jackylee-ch <qcsd2011@gmail.com>
Date: Mon, 28 Sep 2026 22:18:08 +0800
Subject: [PATCH] fix(spec): default PartitionStatistics totalBuckets when
 absent
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`PartitionStatistics::total_buckets` had no serde default, so deserializing
statistics that omit `totalBuckets` — e.g. produced by an older Paimon version
that predates the field, which a REST catalog may still return — failed with a
missing-field error instead of reading the rest of the record. Java treats the
field as `@JsonProperty` on a primitive `int` and documents that it "defaults
to 0 if absent (older Paimon version)".

Add `#[serde(default)]` so the field falls back to 0, matching Java.
---
 .../paimon/src/spec/partition_statistics.rs   | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/crates/paimon/src/spec/partition_statistics.rs b/crates/paimon/src/spec/partition_statistics.rs
index ff82f3144..6f91fee0b 100644
--- a/crates/paimon/src/spec/partition_statistics.rs
+++ b/crates/paimon/src/spec/partition_statistics.rs
@@ -34,5 +34,44 @@ pub struct PartitionStatistics {
     pub file_size_in_bytes: i64,
     pub file_count: i64,
     pub last_file_creation_time: i64,
+    /// Defaults to 0 when absent, e.g. statistics serialized by an older Paimon
+    /// version that predates this field (matches Java `PartitionStatistics`).
+    #[serde(default)]
     pub total_buckets: i32,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn deserializes_without_total_buckets() {
+        // Statistics written by an older Paimon version omit `totalBuckets`; it
+        // must default to 0 rather than failing to deserialize.
+        let json = r#"{
+            "spec": {"dt": "2024-01-01"},
+            "recordCount": 10,
+            "fileSizeInBytes": 2048,
+            "fileCount": 3,
+            "lastFileCreationTime": 1700000000000
+        }"#;
+        let stats: PartitionStatistics = serde_json::from_str(json).unwrap();
+        assert_eq!(stats.total_buckets, 0);
+        assert_eq!(stats.record_count, 10);
+        assert_eq!(stats.file_count, 3);
+    }
+
+    #[test]
+    fn deserializes_with_total_buckets() {
+        let json = r#"{
+            "spec": {},
+            "recordCount": 1,
+            "fileSizeInBytes": 1,
+            "fileCount": 1,
+            "lastFileCreationTime": 0,
+            "totalBuckets": 8
+        }"#;
+        let stats: PartitionStatistics = serde_json::from_str(json).unwrap();
+        assert_eq!(stats.total_buckets, 8);
+    }
+}