feat: implement UpdateMapping and apply meta change to UpdateSchema

src/iceberg/json_serde.cc

@@ -1270,6 +1270,24 @@ Result<std::unique_ptr<NameMapping>> NameMappingFromJson(const nlohmann::json& j
   return NameMapping::Make(std::move(mapped_fields));
 }
 
+std::optional<std::string> UpdateMappingFromJsonString(
+    std::string_view mapping_json, const std::map<int32_t, SchemaField>& updates,
+    const std::multimap<int32_t, int32_t>& adds) {
+  auto json_result = FromJsonString(std::string(mapping_json));
+  if (!json_result) return std::nullopt;
+
+  auto current_mapping = NameMappingFromJson(*json_result);
+  if (!current_mapping) return std::nullopt;
+
+  auto updated_mapping = UpdateMapping(**current_mapping, updates, adds);
+  if (!updated_mapping) return std::nullopt;
+
+  auto json_str = ToJsonString(ToJson(**updated_mapping));
+  if (!json_str) return std::nullopt;
+
+  return std::move(*json_str);
+}
+
 nlohmann::json ToJson(const TableIdentifier& identifier) {
   nlohmann::json json;
   json[kNamespace] = identifier.ns.levels;

src/iceberg/json_serde_internal.h

@@ -19,7 +19,11 @@
 
 #pragma once
 
+#include <map>
 #include <memory>
+#include <optional>
+#include <string>
+#include <string_view>
 
 #include <nlohmann/json_fwd.hpp>
 
@@ -347,6 +351,14 @@ ICEBERG_EXPORT nlohmann::json ToJson(const NameMapping& name_mapping);
 ICEBERG_EXPORT Result<std::unique_ptr<NameMapping>> NameMappingFromJson(
     const nlohmann::json& json);
 
+/// \brief Update a name mapping from its JSON string and return updated JSON.
+///
+/// Parses the JSON, calls UpdateMapping, and serializes the result.
+/// Returns nullopt if any step fails.
+ICEBERG_EXPORT std::optional<std::string> UpdateMappingFromJsonString(
+    std::string_view mapping_json, const std::map<int32_t, SchemaField>& updates,
+    const std::multimap<int32_t, int32_t>& adds);
+
 /// \brief Serializes a `TableIdentifier` object to JSON.
 ///
 /// \param identifier The `TableIdentifier` object to be serialized.

src/iceberg/name_mapping.cc

@@ -323,6 +323,158 @@ class CreateMappingVisitor {
   }
 };
 
+// Visitor class for updating name mappings with schema changes
+class UpdateMappingVisitor {
+ public:
+  UpdateMappingVisitor(const std::map<int32_t, SchemaField>& updates,
+                       const std::multimap<int32_t, int32_t>& adds)
+      : updates_(updates), adds_(adds) {}
+
+  Result<std::unique_ptr<MappedFields>> VisitMapping(const NameMapping& mapping) {
+    auto fields_result = VisitFields(mapping.AsMappedFields());
+    ICEBERG_RETURN_UNEXPECTED(fields_result);
+    return AddNewFields(std::move(*fields_result),
+                        -1 /* parent ID for top-level fields */);
+  }
+
+ private:
+  Result<std::unique_ptr<MappedFields>> VisitFields(const MappedFields& fields) {
+    // Recursively visit all fields
+    std::vector<MappedField> field_results;
+    field_results.reserve(fields.Size());
+
+    for (const auto& field : fields.fields()) {
+      auto field_result = VisitField(field);
+      ICEBERG_RETURN_UNEXPECTED(field_result);
+      field_results.push_back(std::move(*field_result));
+    }
+
+    // Build update assignments map for removing reassigned names
+    std::unordered_map<std::string, int32_t> update_assignments;
+    std::ranges::for_each(field_results, [&](const auto& field) {
+      if (field.field_id.has_value()) {
+        auto update_it = updates_.find(field.field_id.value());
+        if (update_it != updates_.end()) {
+          update_assignments.emplace(std::string(update_it->second.name()),
+                                     field.field_id.value());
+        }
+      }
+    });
+
+    // Remove reassigned names from all fields
+    for (auto& field : field_results) {
+      field = RemoveReassignedNames(field, update_assignments);
+    }
+
+    return MappedFields::Make(std::move(field_results));
+  }
+
+  Result<MappedField> VisitField(const MappedField& field) {
+    // Update this field's names
+    std::unordered_set<std::string> field_names = field.names;
+    if (field.field_id.has_value()) {
+      auto update_it = updates_.find(field.field_id.value());
+      if (update_it != updates_.end()) {
+        field_names.insert(std::string(update_it->second.name()));
+      }
+    }
+
+    std::unique_ptr<MappedFields> nested_mapping = nullptr;
+    if (field.nested_mapping != nullptr) {
+      auto nested_result = VisitFields(*field.nested_mapping);
+      ICEBERG_RETURN_UNEXPECTED(nested_result);
+      nested_mapping = std::move(*nested_result);
+    }
+
+    // Add a new mapping for any new nested fields
+    if (field.field_id.has_value()) {
+      auto nested_result =
+          AddNewFields(std::move(nested_mapping), field.field_id.value());
+      ICEBERG_RETURN_UNEXPECTED(nested_result);
+      nested_mapping = std::move(*nested_result);
+    }
+
+    return MappedField{
+        .names = std::move(field_names),
+        .field_id = field.field_id,
+        .nested_mapping = std::move(nested_mapping),
+    };
+  }
+
+  Result<std::unique_ptr<MappedFields>> AddNewFields(
+      std::unique_ptr<MappedFields> mapping, int32_t parent_id) {
+    auto range = adds_.equal_range(parent_id);
+    std::vector<const SchemaField*> fields_to_add;
+    for (auto it = range.first; it != range.second; ++it) {
+      auto update_it = updates_.find(it->second);
+      if (update_it != updates_.end()) {
+        fields_to_add.push_back(&update_it->second);
+      }
+    }
+
+    if (fields_to_add.empty()) {
+      return std::move(mapping);
+    }
+
+    std::vector<MappedField> new_fields;
+    CreateMappingVisitor create_visitor;
+    for (const auto* field_to_add : fields_to_add) {
+      auto nested_result = VisitType(
+          *field_to_add->type(),
+          [&create_visitor](const auto& type) { return create_visitor.Visit(type); });
+      ICEBERG_RETURN_UNEXPECTED(nested_result);
+
+      new_fields.emplace_back(MappedField{
+          .names = {std::string(field_to_add->name())},
+          .field_id = field_to_add->field_id(),
+          .nested_mapping = std::move(*nested_result),
+      });
+    }
+
+    if (mapping == nullptr || mapping->Size() == 0) {
+      return MappedFields::Make(std::move(new_fields));
+    }
+
+    // Build assignments map for removing reassigned names
+    std::unordered_map<std::string, int32_t> assignments;
+    for (const auto* field_to_add : fields_to_add) {
+      assignments.emplace(std::string(field_to_add->name()), field_to_add->field_id());
+    }
+
+    // create a copy of fields that can be updated (append new fields, replace existing
+    // for reassignment)
+    std::vector<MappedField> fields;
+    fields.reserve(mapping->Size() + new_fields.size());
+    for (const auto& field : mapping->fields()) {
+      fields.push_back(RemoveReassignedNames(field, assignments));
+    }
+
+    fields.insert(fields.end(), std::make_move_iterator(new_fields.begin()),
+                  std::make_move_iterator(new_fields.end()));
+
+    return MappedFields::Make(std::move(fields));
+  }
+
+  static MappedField RemoveReassignedNames(
+      const MappedField& field,
+      const std::unordered_map<std::string, int32_t>& assignments) {
+    std::unordered_set<std::string> updated_names = field.names;
+    std::erase_if(updated_names, [&](const std::string& name) {
+      auto assign_it = assignments.find(name);
+      return assign_it != assignments.end() &&
+             (!field.field_id.has_value() || assign_it->second != field.field_id.value());
+    });
+    return MappedField{
+        .names = std::move(updated_names),
+        .field_id = field.field_id,
+        .nested_mapping = field.nested_mapping,
+    };
+  }
+
+  const std::map<int32_t, SchemaField>& updates_;
+  const std::multimap<int32_t, int32_t>& adds_;
+};
+
 }  // namespace
 
 Result<std::unique_ptr<NameMapping>> CreateMapping(const Schema& schema) {
@@ -335,4 +487,13 @@ Result<std::unique_ptr<NameMapping>> CreateMapping(const Schema& schema) {
   return NameMapping::Make(std::move(*result));
 }
 
+Result<std::unique_ptr<NameMapping>> UpdateMapping(
+    const NameMapping& mapping, const std::map<int32_t, SchemaField>& updates,
+    const std::multimap<int32_t, int32_t>& adds) {
+  UpdateMappingVisitor visitor(updates, adds);
+  auto result = visitor.VisitMapping(mapping);
+  ICEBERG_RETURN_UNEXPECTED(result);
+  return NameMapping::Make(std::move(*result));
+}
+
 }  // namespace iceberg

src/iceberg/name_mapping.h

@@ -20,6 +20,7 @@
 #pragma once
 
 #include <functional>
+#include <map>
 #include <memory>
 #include <optional>
 #include <span>
@@ -143,16 +144,14 @@ ICEBERG_EXPORT std::string ToString(const NameMapping& mapping);
 /// \return A new NameMapping instance initialized with the schema's fields and names.
 ICEBERG_EXPORT Result<std::unique_ptr<NameMapping>> CreateMapping(const Schema& schema);
 
-/// TODO(gangwu): implement this function once SchemaUpdate is supported
-///
 /// \brief Update a name-based mapping using changes to a schema.
 /// \param mapping a name-based mapping
 /// \param updates a map from field ID to updated field definitions
 /// \param adds a map from parent field ID to nested fields to be added
 /// \return an updated mapping with names added to renamed fields and the mapping extended
 /// for new fields
-// ICEBERG_EXPORT Result<std::unique_ptr<NameMapping>> UpdateMapping(
-//     const NameMapping& mapping, const std::map<int32_t, SchemaField>& updates,
-//     const std::multimap<int32_t, int32_t>& adds);
+ICEBERG_EXPORT Result<std::unique_ptr<NameMapping>> UpdateMapping(
+    const NameMapping& mapping, const std::map<int32_t, SchemaField>& updates,
+    const std::multimap<int32_t, int32_t>& adds);
 
 }  // namespace iceberg

src/iceberg/test/CMakeLists.txt

@@ -179,6 +179,7 @@ if(ICEBERG_BUILD_BUNDLE)
                    SOURCES
                    expire_snapshots_test.cc
                    fast_append_test.cc
+                   name_mapping_update_test.cc
                    set_snapshot_test.cc
                    transaction_test.cc
                    update_location_test.cc