improve code

Signed-off-by: chendingchao.cdc <[email protected]>

Author: chendingchao.cdc

src/iceberg/json_internal.cc

@@ -668,13 +668,12 @@ nlohmann::json ToJson(const PartitionSpec& partition_spec) {
 }
 
 Result<std::unique_ptr<PartitionField>> PartitionFieldFromJson(
-    const nlohmann::json& json, bool allow_field_id_missing) {
+    const nlohmann::json& json, std::optional<int32_t> partition_field_id) {
   ICEBERG_ASSIGN_OR_RAISE(auto source_id, GetJsonValue<int32_t>(json, kSourceId));
   int32_t field_id;
-  if (allow_field_id_missing) {
-    // Partition field id in v1 is not tracked, so we use -1 to indicate that.
-    ICEBERG_ASSIGN_OR_RAISE(field_id, GetJsonValueOrDefault<int32_t>(
-                                          json, kFieldId, SchemaField::kInvalidFieldId));
+  if (partition_field_id.has_value()) {
+    // Partition field id in v1 is not tracked, so we use partition_field_id directly.
+    field_id = partition_field_id.value();
   } else {
     ICEBERG_ASSIGN_OR_RAISE(field_id, GetJsonValue<int32_t>(json, kFieldId));
   }
@@ -1053,14 +1052,10 @@ Status ParsePartitionSpecs(const nlohmann::json& json, int8_t format_version,
     int32_t next_partition_field_id = PartitionSpec::kLegacyPartitionDataIdStart;
     std::vector<PartitionField> fields;
     for (const auto& entry_json : partition_spec_json) {
-      ICEBERG_ASSIGN_OR_RAISE(auto field, PartitionFieldFromJson(entry_json, true));
-      int32_t field_id = field->field_id();
-      if (field_id == SchemaField::kInvalidFieldId) {
-        // If the field ID is not set, we need to assign a new one
-        field_id = next_partition_field_id++;
-      }
-      fields.emplace_back(field->source_id(), field_id, std::string(field->name()),
-                          std::move(field->transform()));
+      ICEBERG_ASSIGN_OR_RAISE(
+          auto field, PartitionFieldFromJson(entry_json, next_partition_field_id));
+      next_partition_field_id++;
+      fields.push_back(std::move(*field));
     }
 
     auto spec = std::make_unique<PartitionSpec>(

src/iceberg/json_internal.h

@@ -126,12 +126,13 @@ nlohmann::json ToJson(const PartitionField& partition_field);
 /// and name.
 ///
 /// \param json The JSON object representing a `PartitionField`.
-/// \param allow_field_id_missing Whether the field ID is allowed to be missing. This can
-/// happen when deserializing partition fields from V1 metadata files.
+/// \param partition_field_id If partition_field_id has value, we assign partition fields'
+/// id from partition_field_id. This can happen when deserializing partition fields
+/// from V1 metadata files.
 /// \return An `expected` value containing either a `PartitionField` object or an error.
 /// If the JSON is malformed or missing expected fields, an error will be returned.
 Result<std::unique_ptr<PartitionField>> PartitionFieldFromJson(
-    const nlohmann::json& json, bool allow_field_id_missing = false);
+    const nlohmann::json& json, std::optional<int32_t> partition_field_id = std::nullopt);
 
 /// \brief Serializes a `PartitionSpec` object to JSON.
 ///