diff --git a/dev-doc/updating-c-library.md b/dev-doc/updating-c-library.md
index f5ae9dccd..b54c2d7f6 100644
--- a/dev-doc/updating-c-library.md
+++ b/dev-doc/updating-c-library.md
@@ -19,15 +19,15 @@ for the binding update script (see below) and
 for Flutter (`flutter_libs` and `sync_flutter_libs` plugins) on Linux and Windows:
 
 ```bash
-./tool/set-c-version.sh 4.1.0
+./tool/set-c-version.sh 4.2.0
 ```
 
 ```text
-* Flutter for Linux/Windows, Dart Native: update to [objectbox-c 4.1.0](https://github.com/objectbox/objectbox-c/releases/tag/v4.1.0).
+* Update ObjectBox database for Flutter Linux/Windows, Dart Native apps to [4.2.0](https://github.com/objectbox/objectbox-c/releases/tag/v4.2.0).
 ```
 
 ```text
-Update C library [4.0.2 -> 4.1.0]
+Update C library [4.1.0 -> 4.2.0]
 ```
 
 ### Android
@@ -35,19 +35,19 @@ Update C library [4.0.2 -> 4.1.0]
 For the Flutter plugins on Android ([view releases](https://github.com/objectbox/objectbox-java/releases)):
 
 ```bash
-./tool/set-android-version.sh 4.1.0
+./tool/set-android-version.sh 4.2.0
 ```
 
 ```text
-* Flutter for Android: update to [objectbox-android 4.1.0](https://github.com/objectbox/objectbox-java/releases/tag/V4.1.0).
-  If your project is [using Admin](https://docs.objectbox.io/data-browser#admin-for-android), make sure to
-  update to `io.objectbox:objectbox-android-objectbrowser:4.1.0` in `android/app/build.gradle`.
+* Update ObjectBox database for Flutter Android apps to 4.2.0.
+  If your project is [using Admin](https://docs.objectbox.io/data-browser#admin-for-android), make 
+  sure to update to `io.objectbox:objectbox-android-objectbrowser:4.2.0` in `android/app/build.gradle`.
 ```
 
 ```text
-Update objectbox-android [4.0.3 -> 4.1.0]
+Update objectbox-android [4.1.0 -> 4.2.0]
 
-Bundled with C API 4.1.0 and ObjectBox 4.1.0-2025-01-28
+Bundled with C API 4.2.0 and ObjectBox 4.2.0-2025-03-04
 ```
 
 Note: the embedded C API and ObjectBox version can be looked up
@@ -58,18 +58,18 @@ from the relevant objectbox repository release tag (like `java-4.1.0`).
 For the Flutter plugins on iOS/macOS ([view releases](https://github.com/objectbox/objectbox-swift/releases))
 
 ```bash
-./tool/set-swift-version.sh 4.1.0
+./tool/set-swift-version.sh 4.2.0
 ```
 
 ```text
-* Flutter for iOS/macOS: update to [objectbox-swift 4.1.0](https://github.com/objectbox/objectbox-swift/releases/tag/v4.1.0).
+* Update ObjectBox database for Flutter iOS/macOS apps to 4.2.0.
   For existing projects, run `pod repo update` and `pod update ObjectBox` in the `ios` or `macos` directories.
 ```
 
 ```text
-Update ObjectBox Swift [4.0.0 -> 4.0.1]
+Update ObjectBox Swift [4.1.0 -> 4.2.0]
 
-Bundled with C API 4.1.0 and ObjectBox 4.1.0-2025-01-30
+Bundled with C API 4.2.0 and ObjectBox 4.2.0-2025-03-04
 ```
 
 Note: the embedded C API and ObjectBox version can be looked up 
@@ -96,5 +96,5 @@ Then manually:
 - Commit as
 
 ```text
-Update C-API [4.0.2 -> 4.1.0]
+Update C-API [4.1.0 -> 4.2.0]
 ```
diff --git a/flutter_libs/android/build.gradle b/flutter_libs/android/build.gradle
index 79bf4f154..788a1a9ad 100644
--- a/flutter_libs/android/build.gradle
+++ b/flutter_libs/android/build.gradle
@@ -52,6 +52,6 @@ android {
         // ObjectBox Android library that includes an ObjectBox C library version compatible with
         // the C API binding of the ObjectBox Dart package.
         // https://central.sonatype.com/search?q=g:io.objectbox%20objectbox-android
-        implementation "io.objectbox:objectbox-android:4.1.0"
+        implementation "io.objectbox:objectbox-android:4.2.0"
     }
 }
diff --git a/flutter_libs/ios/objectbox_flutter_libs.podspec b/flutter_libs/ios/objectbox_flutter_libs.podspec
index 3a24c744b..a26696e9d 100644
--- a/flutter_libs/ios/objectbox_flutter_libs.podspec
+++ b/flutter_libs/ios/objectbox_flutter_libs.podspec
@@ -18,7 +18,7 @@ Pod::Spec.new do |s|
   s.source_files     = 'Classes/**/*'
 
   s.dependency 'Flutter'
-  s.dependency 'ObjectBox', '4.1.0'
+  s.dependency 'ObjectBox', '4.2.0'
 
   # Flutter.framework does not contain a i386 slice.
   s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'i386' }
diff --git a/flutter_libs/linux/CMakeLists.txt b/flutter_libs/linux/CMakeLists.txt
index aca438e23..cbce9d6c1 100644
--- a/flutter_libs/linux/CMakeLists.txt
+++ b/flutter_libs/linux/CMakeLists.txt
@@ -44,7 +44,7 @@ target_link_libraries(${PLUGIN_NAME} PRIVATE PkgConfig::GTK)
 # ----------------------------------------------------------------------
 # Download and add objectbox-c prebuilt library.
 
-set(OBJECTBOX_VERSION 4.1.0)
+set(OBJECTBOX_VERSION 4.2.0)
 
 set(OBJECTBOX_ARCH ${CMAKE_SYSTEM_PROCESSOR})
 if (${OBJECTBOX_ARCH} MATCHES "x86_64")
diff --git a/flutter_libs/macos/objectbox_flutter_libs.podspec b/flutter_libs/macos/objectbox_flutter_libs.podspec
index 5dcbcf81d..e6ef1d9af 100644
--- a/flutter_libs/macos/objectbox_flutter_libs.podspec
+++ b/flutter_libs/macos/objectbox_flutter_libs.podspec
@@ -18,7 +18,7 @@ Pod::Spec.new do |s|
   s.source_files     = 'Classes/**/*'
 
   s.dependency 'FlutterMacOS'
-  s.dependency 'ObjectBox', '4.1.0'
+  s.dependency 'ObjectBox', '4.2.0'
 
   s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES' }
   s.swift_version = '5.3'
diff --git a/flutter_libs/windows/CMakeLists.txt b/flutter_libs/windows/CMakeLists.txt
index 77595b411..eed019cbf 100644
--- a/flutter_libs/windows/CMakeLists.txt
+++ b/flutter_libs/windows/CMakeLists.txt
@@ -50,7 +50,7 @@ set(objectbox_flutter_libs_bundled_libraries
 # ----------------------------------------------------------------------
 # Download and add objectbox-c prebuilt library.
 
-set(OBJECTBOX_VERSION 4.1.0)
+set(OBJECTBOX_VERSION 4.2.0)
 
 set(OBJECTBOX_ARCH ${CMAKE_SYSTEM_PROCESSOR})
 if (${OBJECTBOX_ARCH} MATCHES "AMD64")
diff --git a/generator/lib/src/code_builder.dart b/generator/lib/src/code_builder.dart
index f735df13e..f447004b9 100644
--- a/generator/lib/src/code_builder.dart
+++ b/generator/lib/src/code_builder.dart
@@ -1,21 +1,21 @@
 import 'dart:async';
-import 'dart:io';
 import 'dart:convert';
+import 'dart:io';
 
 import 'package:build/build.dart';
 import 'package:collection/collection.dart';
+import 'package:dart_style/dart_style.dart';
 import 'package:glob/glob.dart';
+import 'package:objectbox/internal.dart';
 import 'package:objectbox_generator/src/analysis/analysis.dart';
 import 'package:objectbox_generator/src/builder_dirs.dart';
 import 'package:path/path.dart' as path;
-import 'package:objectbox/internal.dart';
-import 'package:dart_style/dart_style.dart';
-import 'package:source_gen/source_gen.dart';
 import 'package:pubspec_parse/pubspec_parse.dart';
+import 'package:source_gen/source_gen.dart';
 
+import 'code_chunks.dart';
 import 'config.dart';
 import 'entity_resolver.dart';
-import 'code_chunks.dart';
 
 /// CodeBuilder collects all '.objectbox.info' files created by EntityResolver and generates objectbox-model.json and
 /// objectbox_model.dart
@@ -213,6 +213,8 @@ class CodeBuilder extends Builder {
     propInModel.dartFieldType = prop.dartFieldType;
     propInModel.relationTarget = prop.relationTarget;
     propInModel.hnswParams = prop.hnswParams;
+    propInModel.externalType = prop.externalType;
+    propInModel.externalName = prop.externalName;
 
     if (!prop.hasIndexFlag()) {
       propInModel.removeIndex();
@@ -242,6 +244,8 @@ class CodeBuilder extends Builder {
 
     relInModel.name = rel.name;
     relInModel.targetName = rel.targetName;
+    relInModel.externalType = rel.externalType;
+    relInModel.externalName = rel.externalName;
   }
 
   IdUid mergeEntity(ModelInfo modelInfo, ModelEntity entity) {
@@ -267,6 +271,7 @@ class CodeBuilder extends Builder {
 
     entityInModel.name = entity.name;
     entityInModel.flags = entity.flags;
+    entityInModel.externalName = entity.externalName;
     entityInModel.constructorParams = entity.constructorParams;
 
     // here, the entity was found already and entityInModel and entity might differ, i.e. conflicts need to be resolved, so merge all properties first
diff --git a/generator/lib/src/code_chunks.dart b/generator/lib/src/code_chunks.dart
index 336b4bdf5..2fbce137e 100644
--- a/generator/lib/src/code_chunks.dart
+++ b/generator/lib/src/code_chunks.dart
@@ -122,12 +122,16 @@ class CodeChunks {
   }
 
   static String createModelEntity(ModelEntity entity) {
+    var additionalArgs = '';
+    if (entity.externalName != null) {
+      additionalArgs += " externalName: '${entity.externalName}',";
+    }
     return '''
     $obxInt.ModelEntity(
       id: ${createIdUid(entity.id)},
       name: '${entity.name}',
       lastPropertyId: ${createIdUid(entity.lastPropertyId)},
-      flags: ${entity.flags},
+      flags: ${entity.flags},$additionalArgs
       properties: <$obxInt.ModelProperty>[
         ${entity.properties.map(createModelProperty).join(',')}
       ],
@@ -154,6 +158,12 @@ class CodeChunks {
       additionalArgs +=
           ", hnswParams: ${property.hnswParams!.toCodeString(obxInt)}";
     }
+    if (property.externalType != null) {
+      additionalArgs += ", externalType: ${property.externalType!}";
+    }
+    if (property.externalName != null) {
+      additionalArgs += ", externalName: '${property.externalName!}'";
+    }
     return '''
     $obxInt.ModelProperty(
       id: ${createIdUid(property.id)},
@@ -166,11 +176,19 @@ class CodeChunks {
   }
 
   static String createModelRelation(ModelRelation relation) {
+    var additionalArgs = '';
+    if (relation.externalType != null) {
+      additionalArgs += ", externalType: ${relation.externalType!}";
+    }
+    if (relation.externalName != null) {
+      additionalArgs += ", externalName: '${relation.externalName!}'";
+    }
     return '''
     $obxInt.ModelRelation(
       id: ${createIdUid(relation.id)},
       name: '${relation.name}',
       targetId: ${createIdUid(relation.targetId)}
+      $additionalArgs
     )
     ''';
   }
diff --git a/generator/lib/src/entity_resolver.dart b/generator/lib/src/entity_resolver.dart
index eb688718f..03355b962 100644
--- a/generator/lib/src/entity_resolver.dart
+++ b/generator/lib/src/entity_resolver.dart
@@ -28,6 +28,8 @@ class EntityResolver extends Builder {
   final _indexChecker = const TypeChecker.fromRuntime(Index);
   final _backlinkChecker = const TypeChecker.fromRuntime(Backlink);
   final _hnswChecker = const TypeChecker.fromRuntime(HnswIndex);
+  final _externalTypeChecker = const TypeChecker.fromRuntime(ExternalType);
+  final _externalNameChecker = const TypeChecker.fromRuntime(ExternalName);
 
   @override
   FutureOr<void> build(BuildStep buildStep) async {
@@ -68,6 +70,11 @@ class EntityResolver extends Builder {
         null,
         uidRequest: !entityUid.isNull && entityUid.intValue == 0);
 
+    // @ExternalName
+    _externalNameChecker.runIfMatches(classElement, (annotation) {
+      entity.externalName = _readExternalNameParams(annotation);
+    });
+
     // Sync: check if enabled and options
     _syncChecker.runIfMatches(classElement, (annotation) {
       entity.flags |= OBXEntityFlags.SYNC_ENABLED;
@@ -171,6 +178,7 @@ class EntityResolver extends Builder {
       final backlinkAnnotations =
           _backlinkChecker.annotationsOfExact(annotated);
       if (backlinkAnnotations.isNotEmpty) {
+        // Handles ToMany based on other ToOne or ToMany relation (backlink)
         if (!isToManyRel) {
           log.severe(
               "  Skipping property '${f.name}': @Backlink() may only be used with ToMany.");
@@ -183,14 +191,33 @@ class EntityResolver extends Builder {
         entity.backlinks.add(backlink);
         log.info('  $backlink');
       } else if (isToManyRel) {
+        // Handles standalone (non backlink) ToMany relation
+
+        // @ExternalType
+        int? externalType;
+        _externalTypeChecker.runIfMatches(annotated, (annotation) {
+          final externalTypeId = _readExternalTypeParams(annotation);
+          externalType = externalTypeId;
+        });
+
+        // @ExternalName
+        String? externalName;
+        _externalNameChecker.runIfMatches(annotated, (annotation) {
+          externalName = _readExternalNameParams(annotation);
+        });
+
         // create relation
         final rel = ModelRelation.create(IdUid(0, propUid ?? 0), f.name,
             targetName: relTargetName,
-            uidRequest: propUid != null && propUid == 0);
+            uidRequest: propUid != null && propUid == 0,
+            externalName: externalName,
+            externalType: externalType);
+
         entity.relations.add(rel);
 
         log.info('  $rel');
       } else {
+        // Handles regular properties
         // create property (do not use readEntity.createProperty in order to avoid generating new ids)
         final prop = ModelProperty.create(
             IdUid(0, propUid ?? 0), f.name, fieldType,
@@ -226,6 +253,17 @@ class EntityResolver extends Builder {
           _readHnswIndexParams(annotation, prop);
         });
 
+        // @ExternalType
+        _externalTypeChecker.runIfMatches(annotated, (annotation) {
+          final externalTypeId = _readExternalTypeParams(annotation);
+          prop.externalType = externalTypeId;
+        });
+
+        // @ExternalName
+        _externalNameChecker.runIfMatches(annotated, (annotation) {
+          prop.externalName = _readExternalNameParams(annotation);
+        });
+
         // for code generation
         prop.dartFieldType =
             f.type.element!.name! + (isNullable(f.type) ? '?' : '');
@@ -555,6 +593,27 @@ class EntityResolver extends Builder {
             annotation.getField('vectorCacheHintSizeKB')!.toIntValue());
     property.hnswParams = ModelHnswParams.fromAnnotation(hnswRestored);
   }
+
+  int _readExternalTypeParams(DartObject annotation) {
+    final typeIndex =
+        _enumValueIndex(annotation.getField('type')!, "ExternalType.type");
+    final type =
+        typeIndex != null ? ExternalPropertyType.values[typeIndex] : null;
+    if (type == null) {
+      throw InvalidGenerationSourceError(
+          "'type' attribute not specified in @ExternalType annotation");
+    }
+    return externalTypeToOBXExternalType(type);
+  }
+
+  String _readExternalNameParams(DartObject annotation) {
+    final name = annotation.getField('name')!.toStringValue();
+    if (name == null) {
+      throw InvalidGenerationSourceError(
+          "'name' attribute not specified in @ExternalName annotation");
+    }
+    return name;
+  }
 }
 
 extension _TypeCheckerExtensions on TypeChecker {
diff --git a/generator/test/code_builder_test.dart b/generator/test/code_builder_test.dart
index 8bfd7b0e6..29e5cb44d 100644
--- a/generator/test/code_builder_test.dart
+++ b/generator/test/code_builder_test.dart
@@ -378,6 +378,92 @@ void main() {
       expect(idProperty.flags & OBXPropertyFlags.ID_SELF_ASSIGNABLE != 0, true);
     });
   });
+
+  group("ExternalType and ExternalName annotations", () {
+    test('annotations work on @Entity', () async {
+      final source = r'''
+      library example;     
+      import 'package:objectbox/objectbox.dart';
+      
+      @Entity()
+      @ExternalName(name: 'my-mongo-entity')     
+      class Example {
+        @Id()
+        int id = 0;
+      }
+      ''';
+
+      final testEnv = GeneratorTestEnv();
+      await testEnv.run(source);
+
+      final entity = testEnv.model.entities[0];
+      expect(entity.externalName, "my-mongo-entity");
+    });
+
+    test('annotations work on properties', () async {
+      final source = r'''
+      library example;     
+      import 'package:objectbox/objectbox.dart';
+      
+      @Entity()
+      class Example {
+        @Id()
+        int id = 0;
+        
+        @Property(type: PropertyType.byteVector)
+        @ExternalType(type: ExternalPropertyType.mongoId)
+        List<int>? mongoId;
+        
+        @ExternalType(type: ExternalPropertyType.uuid)
+        @ExternalName(name: 'my-mongo-uuid')
+        List<int>? mongoUuid;
+      }
+      ''';
+
+      final testEnv = GeneratorTestEnv();
+      await testEnv.run(source);
+
+      final property1 = testEnv.model.entities[0].properties
+          .firstWhere((element) => element.name == "mongoId");
+      expect(property1.externalType, OBXExternalPropertyType.MongoId);
+
+      final property2 = testEnv.model.entities[0].properties
+          .firstWhere((element) => element.name == "mongoUuid");
+      expect(property2.externalType, OBXExternalPropertyType.Uuid);
+      expect(property2.externalName, "my-mongo-uuid");
+    });
+
+    test('annotations work on ToMany (standalone) relations', () async {
+      final source = r'''
+      library example;     
+      import 'package:objectbox/objectbox.dart';
+      
+      @Entity()
+      class Student{
+        int id;
+        
+        @ExternalType(type: ExternalPropertyType.mongoId)
+        final rel1 = ToMany<Student>();
+        
+        @ExternalType(type: ExternalPropertyType.uuid)
+        @ExternalName(name: 'my-courses-rel')
+        final rel2 = ToMany<Student>();
+      }
+      ''';
+
+      final testEnv = GeneratorTestEnv();
+      await testEnv.run(source);
+
+      final relation1 = testEnv.model.entities[0].relations
+          .firstWhere((element) => element.name == "rel1");
+      expect(relation1.externalType, OBXExternalPropertyType.MongoId);
+
+      final relation2 = testEnv.model.entities[0].relations
+          .firstWhere((element) => element.name == "rel2");
+      expect(relation2.externalType, OBXExternalPropertyType.Uuid);
+      expect(relation2.externalName, "my-courses-rel");
+    });
+  });
 }
 
 Future<PackageConfig> _unsupported() {
diff --git a/install.sh b/install.sh
index 2707c1c6c..bac35583d 100755
--- a/install.sh
+++ b/install.sh
@@ -5,7 +5,7 @@ set -eu
 # It's important that the generated dart bindings and the c-api library version match. Dart won't error on C function
 # signature mismatch, leading to obscure memory bugs.
 # For how to upgrade the version see dev-doc/updating-c-library.md
-cLibVersion=4.1.0
+cLibVersion=4.2.0
 os=$(uname)
 cLibArgs="$*"
 
diff --git a/objectbox/CHANGELOG.md b/objectbox/CHANGELOG.md
index f94cf4bac..cc1de67c7 100644
--- a/objectbox/CHANGELOG.md
+++ b/objectbox/CHANGELOG.md
@@ -4,6 +4,12 @@
 * Examples: demos are compatible with JDK 21 included with Android Studio Ladybug or later, require
   Flutter SDK 3.24 (with Dart SDK 3.5) or newer.
 * Requires at least Dart SDK 3.4 or Flutter SDK 3.22.
+* Update ObjectBox database for Flutter Linux/Windows, Dart Native apps to [4.2.0](https://github.com/objectbox/objectbox-c/releases/tag/v4.2.0).
+* Update ObjectBox database for Flutter Android apps to 4.2.0.
+  If your project is [using Admin](https://docs.objectbox.io/data-browser#admin-for-android), make
+  sure to update to `io.objectbox:objectbox-android-objectbrowser:4.2.0` in `android/app/build.gradle`.
+* Update ObjectBox database for Flutter iOS/macOS apps to 4.2.0.
+  For existing projects, run `pod repo update` and `pod update ObjectBox` in the `ios` or `macos` directories.
 
 ## 4.1.0 (2025-02-04)
 
diff --git a/objectbox/example/flutter/objectbox_demo_relations/android/app/build.gradle b/objectbox/example/flutter/objectbox_demo_relations/android/app/build.gradle
index 56fc22b7e..5da6c3569 100644
--- a/objectbox/example/flutter/objectbox_demo_relations/android/app/build.gradle
+++ b/objectbox/example/flutter/objectbox_demo_relations/android/app/build.gradle
@@ -83,5 +83,5 @@ dependencies {
     // Add the Android library with ObjectBox Admin only for debug builds.
     // Note: when the objectbox package updates, check if the Android
     // library below needs to be updated as well.
-    debugImplementation("io.objectbox:objectbox-android-objectbrowser:4.1.0")
+    debugImplementation("io.objectbox:objectbox-android-objectbrowser:4.2.0")
 }
diff --git a/objectbox/lib/src/annotations.dart b/objectbox/lib/src/annotations.dart
index 44c20582d..690e58105 100644
--- a/objectbox/lib/src/annotations.dart
+++ b/objectbox/lib/src/annotations.dart
@@ -487,3 +487,124 @@ class HnswIndex {
       this.reparationBacklinkProbability,
       this.vectorCacheHintSizeKB});
 }
+
+/// A property type of an external system (e.g. another database) that has no
+/// default mapping to an ObjectBox type.
+///
+/// Use with [ExternalType].
+enum ExternalPropertyType {
+  /// Representing type: ByteVector
+  ///
+  /// Encoding: 1:1 binary representation, little endian (16 bytes)
+  int128,
+
+  /// Representing type: ByteVector
+  ///
+  /// Encoding: 1:1 binary representation (16 bytes)
+  uuid,
+
+  /// IEEE 754 decimal128 type, e.g. supported by MongoDB.
+  ///
+  /// Representing type: ByteVector
+  ///
+  /// Encoding: 1:1 binary representation (16 bytes)
+  decimal128,
+
+  /// A key/value map; e.g. corresponds to a JSON object or a MongoDB document
+  /// (although not keeping the key order).
+  ///
+  /// Unlike the Flex type, this must contain a map value (e.g. not a vector or
+  /// a scalar).
+  ///
+  /// Representing type: Flex
+  ///
+  /// Encoding: Flex
+  flexMap,
+
+  /// A vector (aka list or array) of flexible elements; e.g. corresponds to a
+  /// JSON array or a MongoDB array.
+  ///
+  /// Unlike the Flex type, this must contain a vector value (e.g. not a map or
+  /// a scalar).
+  ///
+  /// Representing type: Flex
+  ///
+  /// Encoding: Flex
+  flexVector,
+
+  /// Placeholder (not yet used) for a JSON document.
+  ///
+  /// Representing type: String
+  json,
+
+  /// Placeholder (not yet used) for a BSON document.
+  ///
+  /// Representing type: ByteVector
+  bson,
+
+  /// JavaScript source code.
+  ///
+  /// Representing type: String
+  javaScript,
+
+  /// A vector (array) of Int128 values.
+  int128Vector,
+
+  /// A vector (array) of Int128 values
+  uuidVector,
+
+  /// The 12-byte ObjectId type in MongoDB.
+  ///
+  /// Representing type: ByteVector
+  ///
+  /// Encoding: 1:1 binary representation (12 bytes)
+  mongoId,
+
+  /// A vector (array) of MongoId values.
+  mongoIdVector,
+
+  /// Representing type: Long
+  ///
+  /// Encoding: Two unsigned 32-bit integers merged into a 64-bit integer.
+  mongoTimestamp,
+
+  /// Representing type: ByteVector
+  ///
+  /// Encoding: 3 zero bytes (reserved, functions as padding), fourth byte is
+  /// the sub-type, followed by the binary data.
+  mongoBinary,
+
+  /// Representing type: string vector with 2 elements (index 0: pattern,
+  /// index 1: options)
+  ///
+  /// Encoding: 1:1 string representation
+  mongoRegex
+}
+
+/// See the constructor documentation.
+class ExternalType {
+  /// The type of the property in the external system.
+  ///
+  /// See [ExternalPropertyType] for possible values.
+  final ExternalPropertyType type;
+
+  /// Sets the type of a property or the type of object IDs of a [ToMany] in an
+  /// external system (like another database).
+  ///
+  /// This is useful if there is no default mapping of the ObjectBox type to the
+  /// type in the external system.
+  ///
+  /// Carefully look at the documentation of the external type to ensure it is
+  /// compatible with the ObjectBox type.
+  const ExternalType({required this.type});
+}
+
+/// See the constructor documentation.
+class ExternalName {
+  /// The name assigned to the property in the external system.
+  final String name;
+
+  /// Sets the name of an @Entity, a property or a [ToMany] in an external
+  /// system (like another database).
+  const ExternalName({required this.name});
+}
diff --git a/objectbox/lib/src/modelinfo/enums.dart b/objectbox/lib/src/modelinfo/enums.dart
index 2ebb7067d..d422dcebb 100644
--- a/objectbox/lib/src/modelinfo/enums.dart
+++ b/objectbox/lib/src/modelinfo/enums.dart
@@ -239,3 +239,112 @@ abstract class OBXPropertyType {
   /// < Variable sized vector of Date values (high precision 64-bit timestamp).
   static const int DateNanoVector = 32;
 }
+
+int externalTypeToOBXExternalType(ExternalPropertyType type) {
+  switch (type) {
+    case ExternalPropertyType.int128:
+      return OBXExternalPropertyType.Int128;
+    case ExternalPropertyType.uuid:
+      return OBXExternalPropertyType.Uuid;
+    case ExternalPropertyType.decimal128:
+      return OBXExternalPropertyType.Decimal128;
+    case ExternalPropertyType.flexMap:
+      return OBXExternalPropertyType.FlexMap;
+    case ExternalPropertyType.flexVector:
+      return OBXExternalPropertyType.FlexVector;
+    case ExternalPropertyType.json:
+      return OBXExternalPropertyType.Json;
+    case ExternalPropertyType.bson:
+      return OBXExternalPropertyType.Bson;
+    case ExternalPropertyType.javaScript:
+      return OBXExternalPropertyType.JavaScript;
+    case ExternalPropertyType.int128Vector:
+      return OBXExternalPropertyType.Int128Vector;
+    case ExternalPropertyType.uuidVector:
+      return OBXExternalPropertyType.UuidVector;
+    case ExternalPropertyType.mongoId:
+      return OBXExternalPropertyType.MongoId;
+    case ExternalPropertyType.mongoIdVector:
+      return OBXExternalPropertyType.MongoIdVector;
+    case ExternalPropertyType.mongoTimestamp:
+      return OBXExternalPropertyType.MongoTimestamp;
+    case ExternalPropertyType.mongoBinary:
+      return OBXExternalPropertyType.MongoBinary;
+    case ExternalPropertyType.mongoRegex:
+      return OBXExternalPropertyType.MongoRegex;
+    default:
+      throw ArgumentError.value(type, 'type', 'Invalid ExternalType');
+  }
+}
+
+/// A property type of an external system (e.g. another database) that has no default mapping to an ObjectBox type.
+/// External property types numeric values start at 100 to avoid overlaps with ObjectBox's PropertyType.
+/// (And if we ever support one of these as a primary type, we could share the numeric value?)
+abstract class OBXExternalPropertyType {
+  /// Not a real type: represents uninitialized state and can be used for forward compatibility.
+  static const int Unknown = 0;
+
+  /// Representing type: ByteVector
+  /// Encoding: 1:1 binary representation, little endian (16 bytes)
+  static const int Int128 = 100;
+
+  /// Representing type: ByteVector
+  /// Encoding: 1:1 binary representation (16 bytes)
+  static const int Uuid = 102;
+
+  /// IEEE 754 decimal128 type, e.g. supported by MongoDB
+  /// Representing type: ByteVector
+  /// Encoding: 1:1 binary representation (16 bytes)
+  static const int Decimal128 = 103;
+
+  /// A key/value map; e.g. corresponds to a JSON object or a MongoDB document (although not keeping the key order).
+  /// Unlike the Flex type, this must contain a map value (e.g. not a vector or a scalar).
+  /// Representing type: Flex
+  /// Encoding: Flex
+  static const int FlexMap = 107;
+
+  /// A vector (aka list or array) of flexible elements; e.g. corresponds to a JSON array or a MongoDB array.
+  /// Unlike the Flex type, this must contain a vector value (e.g. not a map or a scalar).
+  /// Representing type: Flex
+  /// Encoding: Flex
+  static const int FlexVector = 108;
+
+  /// Placeholder (not yet used) for a JSON document.
+  /// Representing type: String
+  static const int Json = 109;
+
+  /// Placeholder (not yet used) for a BSON document.
+  /// Representing type: ByteVector
+  static const int Bson = 110;
+
+  /// JavaScript source code
+  /// Representing type: String
+  static const int JavaScript = 111;
+
+  /// A vector (array) of Int128 values
+  static const int Int128Vector = 116;
+
+  /// A vector (array) of Int128 values
+  static const int UuidVector = 118;
+
+  /// The 12-byte ObjectId type in MongoDB
+  /// Representing type: ByteVector
+  /// Encoding: 1:1 binary representation (12 bytes)
+  static const int MongoId = 123;
+
+  /// A vector (array) of MongoId values
+  static const int MongoIdVector = 124;
+
+  /// Representing type: Long
+  /// Encoding: Two unsigned 32-bit integers merged into a 64-bit integer.
+  static const int MongoTimestamp = 125;
+
+  /// Representing type: ByteVector
+  /// Encoding: 3 zero bytes (reserved, functions as padding), fourth byte is the sub-type,
+  /// followed by the binary data.
+  static const int MongoBinary = 126;
+
+  /// Representing type: string vector with 2 elements (index 0: pattern, index 1: options)
+  /// Encoding: 1:1 string representation
+  static const int MongoRegex = 127;
+}
diff --git a/objectbox/lib/src/modelinfo/modelentity.dart b/objectbox/lib/src/modelinfo/modelentity.dart
index e15ac526d..e5c0f0346 100644
--- a/objectbox/lib/src/modelinfo/modelentity.dart
+++ b/objectbox/lib/src/modelinfo/modelentity.dart
@@ -14,6 +14,7 @@ class ModelEntity {
   late String _name;
   IdUid lastPropertyId = const IdUid.empty();
   int _flags = 0;
+  String? externalName;
   final List<ModelProperty> _properties;
   final List<ModelRelation> _relations;
   final List<ModelBacklink> _backlinks;
@@ -72,6 +73,7 @@ class ModelEntity {
       required String name,
       required this.lastPropertyId,
       required int flags,
+      this.externalName,
       required List<ModelProperty> properties,
       required List<ModelRelation> relations,
       required List<ModelBacklink> backlinks})
@@ -94,6 +96,7 @@ class ModelEntity {
         _backlinks = [] {
     name = data['name'] as String?;
     flags = data['flags'] as int? ?? 0;
+    externalName = data['externalName'] as String?;
 
     final properties = data['properties'] as List;
     for (final p in properties) {
@@ -179,6 +182,7 @@ class ModelEntity {
     ret['lastPropertyId'] = lastPropertyId.toString();
     ret['name'] = name;
     if (flags != 0) ret['flags'] = flags;
+    if (externalName != null) ret['externalName'] = externalName;
     ret['properties'] =
         properties.map((p) => p.toMap(forModelJson: forModelJson)).toList();
     ret['relations'] =
diff --git a/objectbox/lib/src/modelinfo/modelproperty.dart b/objectbox/lib/src/modelinfo/modelproperty.dart
index 2ff57c6cc..30c720d8f 100644
--- a/objectbox/lib/src/modelinfo/modelproperty.dart
+++ b/objectbox/lib/src/modelinfo/modelproperty.dart
@@ -16,6 +16,8 @@ class ModelProperty {
   ModelEntity? entity;
   String? relationTarget;
   ModelHnswParams? hnswParams;
+  int? externalType;
+  String? externalName;
 
   /// Type used in the source dart code - used by the code generator.
   /// Starts with [_fieldReadOnlyPrefix] if the field (currently IDs only) is
@@ -114,7 +116,9 @@ class ModelProperty {
       required int flags,
       IdUid? indexId,
       this.relationTarget,
-      this.hnswParams})
+      this.hnswParams,
+      this.externalName,
+      this.externalType})
       : _name = name,
         _type = type,
         _flags = flags,
@@ -127,7 +131,9 @@ class ModelProperty {
         _dartFieldType = data['dartFieldType'] as String?,
         uidRequest = data['uidRequest'] as bool? ?? false,
         hnswParams = ModelHnswParams.fromMap(
-            data['hnswParams'] as Map<String, dynamic>?) {
+            data['hnswParams'] as Map<String, dynamic>?),
+        externalType = data['externalType'] as int?,
+        externalName = data['externalName'] as String? {
     name = data['name'] as String?;
     type = data['type'] as int?;
     flags = data['flags'] as int? ?? 0;
@@ -140,6 +146,8 @@ class ModelProperty {
     ret['id'] = id.toString();
     ret['name'] = name;
     ret['type'] = type;
+    if (externalType != null) ret['externalType'] = externalType;
+    if (externalName != null) ret['externalName'] = externalName;
     if (flags != 0) ret['flags'] = flags;
     if (indexId != null) ret['indexId'] = indexId!.toString();
     if (relationTarget != null) ret['relationTarget'] = relationTarget;
diff --git a/objectbox/lib/src/modelinfo/modelrelation.dart b/objectbox/lib/src/modelinfo/modelrelation.dart
index f8c275004..cad53f851 100644
--- a/objectbox/lib/src/modelinfo/modelrelation.dart
+++ b/objectbox/lib/src/modelinfo/modelrelation.dart
@@ -12,6 +12,9 @@ class ModelRelation {
 
   String? _targetName;
 
+  int? externalType;
+  String? externalName;
+
   // whether the user requested UID information (started a rename process)
   final bool uidRequest;
 
@@ -44,15 +47,29 @@ class ModelRelation {
 
   // used in code generator
   ModelRelation.create(this.id, String? name,
-      {String? targetId, String? targetName, this.uidRequest = false}) {
+      {String? targetId,
+      String? targetName,
+      int? externalType,
+      String? externalName,
+      this.uidRequest = false}) {
     this.name = name;
     if (targetId != null) this.targetId = IdUid.fromString(targetId);
     if (targetName != null) this.targetName = targetName;
+    if (externalType != null) {
+      this.externalType = externalType;
+    }
+    if (externalName != null) {
+      this.externalName = externalName;
+    }
   }
 
   // used in generated code
   ModelRelation(
-      {required this.id, required String name, required IdUid targetId})
+      {required this.id,
+      required String name,
+      required IdUid targetId,
+      this.externalName,
+      this.externalType})
       : _name = name,
         _targetId = targetId,
         uidRequest = false;
@@ -62,13 +79,21 @@ class ModelRelation {
             IdUid.fromString(data['id'] as String?), data['name'] as String?,
             targetId: data['targetId'] as String?,
             targetName: data['targetName'] as String?,
-            uidRequest: data['uidRequest'] as bool? ?? false);
+            uidRequest: data['uidRequest'] as bool? ?? false,
+            externalType: data['externalType'] as int?,
+            externalName: data['externalName'] as String?);
 
   Map<String, dynamic> toMap({bool forModelJson = false}) {
     final ret = <String, dynamic>{};
     ret['id'] = id.toString();
     ret['name'] = name;
     if (_targetId != null) ret['targetId'] = _targetId.toString();
+    if (externalType != null) {
+      ret['externalType'] = externalType;
+    }
+    if (externalName != null) {
+      ret['externalName'] = externalName;
+    }
     if (!forModelJson) {
       ret['targetName'] = _targetName;
       ret['uidRequest'] = uidRequest;
diff --git a/objectbox/lib/src/native/bindings/objectbox-sync.h b/objectbox/lib/src/native/bindings/objectbox-sync.h
index 2a154f39d..109bc8a3f 100644
--- a/objectbox/lib/src/native/bindings/objectbox-sync.h
+++ b/objectbox/lib/src/native/bindings/objectbox-sync.h
@@ -34,7 +34,7 @@
 #include "objectbox.h"
 
 #if defined(static_assert) || defined(__cplusplus)
-static_assert(OBX_VERSION_MAJOR == 4 && OBX_VERSION_MINOR == 1 && OBX_VERSION_PATCH == 0,  // NOLINT
+static_assert(OBX_VERSION_MAJOR == 4 && OBX_VERSION_MINOR == 2 && OBX_VERSION_PATCH == 0,  // NOLINT
               "Versions of objectbox.h and objectbox-sync.h files do not match, please update");
 #endif
 
diff --git a/objectbox/lib/src/native/bindings/objectbox.h b/objectbox/lib/src/native/bindings/objectbox.h
index 6973625cd..22a9602f3 100644
--- a/objectbox/lib/src/native/bindings/objectbox.h
+++ b/objectbox/lib/src/native/bindings/objectbox.h
@@ -52,7 +52,7 @@ extern "C" {
 /// When using ObjectBox as a dynamic library, you should verify that a compatible version was linked using
 /// obx_version() or obx_version_is_at_least().
 #define OBX_VERSION_MAJOR 4
-#define OBX_VERSION_MINOR 1
+#define OBX_VERSION_MINOR 2
 #define OBX_VERSION_PATCH 0  // values >= 100 are reserved for dev releases leading to the next minor/major increase
 
 //----------------------------------------------
@@ -615,6 +615,76 @@ typedef enum {
     OBXPropertyFlags_EXPIRATION_TIME = 65536,
 } OBXPropertyFlags;
 
+/// A property type of an external system (e.g. another database) that has no default mapping to an ObjectBox type.
+/// External property types numeric values start at 100 to avoid overlaps with ObjectBox's PropertyType.
+/// (And if we ever support one of these as a primary type, we could share the numeric value?)
+typedef enum {
+    /// Not a real type: represents uninitialized state and can be used for forward compatibility.
+    OBXExternalPropertyType_Unknown = 0,
+    /// Representing type: ByteVector
+    /// Encoding: 1:1 binary representation, little endian (16 bytes)
+    OBXExternalPropertyType_Int128 = 100,
+    // OBXExternalPropertyType_Reserved1 = 101,
+    /// Representing type: ByteVector
+    /// Encoding: 1:1 binary representation (16 bytes)
+    OBXExternalPropertyType_Uuid = 102,
+    /// IEEE 754 decimal128 type, e.g. supported by MongoDB
+    /// Representing type: ByteVector
+    /// Encoding: 1:1 binary representation (16 bytes)
+    OBXExternalPropertyType_Decimal128 = 103,
+    // OBXExternalPropertyType_Reserved2 = 104,
+    // OBXExternalPropertyType_Reserved3 = 105,
+    // OBXExternalPropertyType_Reserved4 = 106,
+    /// A key/value map; e.g. corresponds to a JSON object or a MongoDB document (although not keeping the key order).
+    /// Unlike the Flex type, this must contain a map value (e.g. not a vector or a scalar).
+    /// Representing type: Flex
+    /// Encoding: Flex
+    OBXExternalPropertyType_FlexMap = 107,
+    /// A vector (aka list or array) of flexible elements; e.g. corresponds to a JSON array or a MongoDB array.
+    /// Unlike the Flex type, this must contain a vector value (e.g. not a map or a scalar).
+    /// Representing type: Flex
+    /// Encoding: Flex
+    OBXExternalPropertyType_FlexVector = 108,
+    /// Placeholder (not yet used) for a JSON document.
+    /// Representing type: String
+    OBXExternalPropertyType_Json = 109,
+    /// Placeholder (not yet used) for a BSON document.
+    /// Representing type: ByteVector
+    OBXExternalPropertyType_Bson = 110,
+    /// JavaScript source code
+    /// Representing type: String
+    OBXExternalPropertyType_JavaScript = 111,
+    // OBXExternalPropertyType_Reserved5 = 112,
+    // OBXExternalPropertyType_Reserved6 = 113,
+    // OBXExternalPropertyType_Reserved7 = 114,
+    // OBXExternalPropertyType_Reserved8 = 115,
+    /// A vector (array) of Int128 values
+    OBXExternalPropertyType_Int128Vector = 116,
+    // OBXExternalPropertyType_Reserved9 = 117,
+    /// A vector (array) of Int128 values
+    OBXExternalPropertyType_UuidVector = 118,
+    // OBXExternalPropertyType_Reserved10 = 119,
+    // OBXExternalPropertyType_Reserved11 = 120,
+    // OBXExternalPropertyType_Reserved12 = 121,
+    // OBXExternalPropertyType_Reserved13 = 122,
+    /// The 12-byte ObjectId type in MongoDB
+    /// Representing type: ByteVector
+    /// Encoding: 1:1 binary representation (12 bytes)
+    OBXExternalPropertyType_MongoId = 123,
+    /// A vector (array) of MongoId values
+    OBXExternalPropertyType_MongoIdVector = 124,
+    /// Representing type: Long
+    /// Encoding: Two unsigned 32-bit integers merged into a 64-bit integer.
+    OBXExternalPropertyType_MongoTimestamp = 125,
+    /// Representing type: ByteVector
+    /// Encoding: 3 zero bytes (reserved, functions as padding), fourth byte is the sub-type,
+    /// followed by the binary data.
+    OBXExternalPropertyType_MongoBinary = 126,
+    /// Representing type: string vector with 2 elements (index 0: pattern, index 1: options)
+    /// Encoding: 1:1 string representation
+    OBXExternalPropertyType_MongoRegex = 127,
+} OBXExternalPropertyType;
+
 struct OBX_model;  // doxygen (only) picks up the typedef struct below
 
 /// Model represents a database schema and must be provided when opening the store.
@@ -657,6 +727,14 @@ OBX_C_API obx_err obx_model_entity(OBX_model* model, const char* name, obx_schem
 /// @param flags See OBXEntityFlags for values (use bitwise OR to combine multiple flags)
 OBX_C_API obx_err obx_model_entity_flags(OBX_model* model, uint32_t flags);
 
+/// Set the highest ever known property id in the entity. Should always be equal to or higher than the
+/// last property id of the previous version of the entity.
+OBX_C_API obx_err obx_model_entity_last_property_id(OBX_model* model, obx_schema_id property_id, obx_uid property_uid);
+
+/// Refine the definition of the entity declared by the most recent obx_model_entity() call: set the external name.
+/// This is an optional name used in an external system, e.g. another database that ObjectBox syncs with.
+OBX_C_API obx_err obx_model_entity_external_name(OBX_model* model, const char* external_name);
+
 /// Starts the definition of a new property for the entity type of the last obx_model_entity() call.
 /// @param name A human readable name for the property. Must be unique within the entity
 /// @param type The type of property required
@@ -682,6 +760,19 @@ OBX_C_API obx_err obx_model_property_relation(OBX_model* model, const char* targ
 /// @param index_uid Used to identify relations between versions of the model. Must be globally unique.
 OBX_C_API obx_err obx_model_property_index_id(OBX_model* model, obx_schema_id index_id, obx_uid index_uid);
 
+/// Refine the definition of the property declared by the most recent obx_model_property() call: set the external name.
+/// This is an optional name used in an external system, e.g. another database that ObjectBox syncs with.
+/// @param index_id Must be unique within this version of the model
+/// @param index_uid Used to identify relations between versions of the model. Must be globally unique.
+OBX_C_API obx_err obx_model_property_external_name(OBX_model* model, const char* external_name);
+
+/// Refine the definition of the property declared by the most recent obx_model_property() call: set the external type.
+/// This is an optional type used in an external system, e.g. another database that ObjectBox syncs with.
+/// Note that the supported mappings from ObjectBox types to external types are limited.
+/// @param index_id Must be unique within this version of the model
+/// @param index_uid Used to identify relations between versions of the model. Must be globally unique.
+OBX_C_API obx_err obx_model_property_external_type(OBX_model* model, OBXExternalPropertyType external_type);
+
 /// Sets the vector dimensionality for the HNSW index of the latest property (must be of a supported vector type).
 /// This a mandatory option for all HNSW indexes.
 /// Note 1: vectors with higher dimensions than this value are also indexed (ignoring the higher elements).
@@ -702,7 +793,7 @@ OBX_C_API obx_err obx_model_property_index_hnsw_neighbors_per_node(OBX_model* mo
 /// If indexing time is not a major concern, a value of at least 200 is recommended to improve search quality.
 OBX_C_API obx_err obx_model_property_index_hnsw_indexing_search_count(OBX_model* model, uint32_t value);
 
-/// Sets flags for the HNSW index of the latest property ().
+/// Sets flags for the HNSW index of the latest property.
 /// For details see OBXHnswFlags and its individual values.
 /// @param flags See OBXHnswFlags for values (use bitwise OR to combine multiple flags)
 OBX_C_API obx_err obx_model_property_index_hnsw_flags(OBX_model* model, uint32_t flags);
@@ -728,6 +819,15 @@ OBX_C_API obx_err obx_model_property_index_hnsw_vector_cache_hint_size_kb(OBX_mo
 OBX_C_API obx_err obx_model_relation(OBX_model* model, obx_schema_id relation_id, obx_uid relation_uid,
                                      obx_schema_id target_id, obx_uid target_uid);
 
+/// Augments the previously defined relation with a name
+OBX_C_API obx_err obx_model_relation_name(OBX_model* model, const char* name);
+
+/// Augments the previously defined relation with an external name (used outside of ObjectBox)
+OBX_C_API obx_err obx_model_relation_external_name(OBX_model* model, const char* external_name);
+
+/// Augments the previously defined relation with an external type (used outside of ObjectBox)
+OBX_C_API obx_err obx_model_relation_external_type(OBX_model* model, OBXExternalPropertyType external_type);
+
 /// Set the highest ever known entity id in the model. Should always be equal to or higher than the
 /// last entity id of the previous version of the model
 OBX_C_API void obx_model_last_entity_id(OBX_model*, obx_schema_id entity_id, obx_uid entity_uid);
@@ -740,10 +840,6 @@ OBX_C_API void obx_model_last_index_id(OBX_model* model, obx_schema_id index_id,
 /// last relation id of the previous version of the model.
 OBX_C_API void obx_model_last_relation_id(OBX_model* model, obx_schema_id relation_id, obx_uid relation_uid);
 
-/// Set the highest ever known property id in the entity. Should always be equal to or higher than the
-/// last property id of the previous version of the entity.
-OBX_C_API obx_err obx_model_entity_last_property_id(OBX_model* model, obx_schema_id property_id, obx_uid property_uid);
-
 //----------------------------------------------
 // Store
 //----------------------------------------------
diff --git a/objectbox/lib/src/native/bindings/objectbox_c.dart b/objectbox/lib/src/native/bindings/objectbox_c.dart
index 702343fda..4a26aa2a5 100644
--- a/objectbox/lib/src/native/bindings/objectbox_c.dart
+++ b/objectbox/lib/src/native/bindings/objectbox_c.dart
@@ -427,6 +427,47 @@ class ObjectBoxC {
   late final _model_entity_flags = _model_entity_flagsPtr
       .asFunction<int Function(ffi.Pointer<OBX_model>, int)>();
 
+  /// Set the highest ever known property id in the entity. Should always be equal to or higher than the
+  /// last property id of the previous version of the entity.
+  int model_entity_last_property_id(
+    ffi.Pointer<OBX_model> model,
+    int property_id,
+    int property_uid,
+  ) {
+    return _model_entity_last_property_id(
+      model,
+      property_id,
+      property_uid,
+    );
+  }
+
+  late final _model_entity_last_property_idPtr = _lookup<
+      ffi.NativeFunction<
+          obx_err Function(ffi.Pointer<OBX_model>, obx_schema_id,
+              obx_uid)>>('obx_model_entity_last_property_id');
+  late final _model_entity_last_property_id = _model_entity_last_property_idPtr
+      .asFunction<int Function(ffi.Pointer<OBX_model>, int, int)>();
+
+  /// Refine the definition of the entity declared by the most recent obx_model_entity() call: set the external name.
+  /// This is an optional name used in an external system, e.g. another database that ObjectBox syncs with.
+  int model_entity_external_name(
+    ffi.Pointer<OBX_model> model,
+    ffi.Pointer<ffi.Char> external_name,
+  ) {
+    return _model_entity_external_name(
+      model,
+      external_name,
+    );
+  }
+
+  late final _model_entity_external_namePtr = _lookup<
+      ffi.NativeFunction<
+          obx_err Function(ffi.Pointer<OBX_model>,
+              ffi.Pointer<ffi.Char>)>>('obx_model_entity_external_name');
+  late final _model_entity_external_name =
+      _model_entity_external_namePtr.asFunction<
+          int Function(ffi.Pointer<OBX_model>, ffi.Pointer<ffi.Char>)>();
+
   /// Starts the definition of a new property for the entity type of the last obx_model_entity() call.
   /// @param name A human readable name for the property. Must be unique within the entity
   /// @param type The type of property required
@@ -523,6 +564,50 @@ class ObjectBoxC {
   late final _model_property_index_id = _model_property_index_idPtr
       .asFunction<int Function(ffi.Pointer<OBX_model>, int, int)>();
 
+  /// Refine the definition of the property declared by the most recent obx_model_property() call: set the external name.
+  /// This is an optional name used in an external system, e.g. another database that ObjectBox syncs with.
+  /// @param index_id Must be unique within this version of the model
+  /// @param index_uid Used to identify relations between versions of the model. Must be globally unique.
+  int model_property_external_name(
+    ffi.Pointer<OBX_model> model,
+    ffi.Pointer<ffi.Char> external_name,
+  ) {
+    return _model_property_external_name(
+      model,
+      external_name,
+    );
+  }
+
+  late final _model_property_external_namePtr = _lookup<
+      ffi.NativeFunction<
+          obx_err Function(ffi.Pointer<OBX_model>,
+              ffi.Pointer<ffi.Char>)>>('obx_model_property_external_name');
+  late final _model_property_external_name =
+      _model_property_external_namePtr.asFunction<
+          int Function(ffi.Pointer<OBX_model>, ffi.Pointer<ffi.Char>)>();
+
+  /// Refine the definition of the property declared by the most recent obx_model_property() call: set the external type.
+  /// This is an optional type used in an external system, e.g. another database that ObjectBox syncs with.
+  /// Note that the supported mappings from ObjectBox types to external types are limited.
+  /// @param index_id Must be unique within this version of the model
+  /// @param index_uid Used to identify relations between versions of the model. Must be globally unique.
+  int model_property_external_type(
+    ffi.Pointer<OBX_model> model,
+    int external_type,
+  ) {
+    return _model_property_external_type(
+      model,
+      external_type,
+    );
+  }
+
+  late final _model_property_external_typePtr = _lookup<
+          ffi
+          .NativeFunction<obx_err Function(ffi.Pointer<OBX_model>, ffi.Int32)>>(
+      'obx_model_property_external_type');
+  late final _model_property_external_type = _model_property_external_typePtr
+      .asFunction<int Function(ffi.Pointer<OBX_model>, int)>();
+
   /// Sets the vector dimensionality for the HNSW index of the latest property (must be of a supported vector type).
   /// This a mandatory option for all HNSW indexes.
   /// Note 1: vectors with higher dimensions than this value are also indexed (ignoring the higher elements).
@@ -591,7 +676,7 @@ class ObjectBoxC {
       _model_property_index_hnsw_indexing_search_countPtr
           .asFunction<int Function(ffi.Pointer<OBX_model>, int)>();
 
-  /// Sets flags for the HNSW index of the latest property ().
+  /// Sets flags for the HNSW index of the latest property.
   /// For details see OBXHnswFlags and its individual values.
   /// @param flags See OBXHnswFlags for values (use bitwise OR to combine multiple flags)
   int model_property_index_hnsw_flags(
@@ -702,6 +787,61 @@ class ObjectBoxC {
   late final _model_relation = _model_relationPtr
       .asFunction<int Function(ffi.Pointer<OBX_model>, int, int, int, int)>();
 
+  /// Augments the previously defined relation with a name
+  int model_relation_name(
+    ffi.Pointer<OBX_model> model,
+    ffi.Pointer<ffi.Char> name,
+  ) {
+    return _model_relation_name(
+      model,
+      name,
+    );
+  }
+
+  late final _model_relation_namePtr = _lookup<
+      ffi.NativeFunction<
+          obx_err Function(ffi.Pointer<OBX_model>,
+              ffi.Pointer<ffi.Char>)>>('obx_model_relation_name');
+  late final _model_relation_name = _model_relation_namePtr.asFunction<
+      int Function(ffi.Pointer<OBX_model>, ffi.Pointer<ffi.Char>)>();
+
+  /// Augments the previously defined relation with an external name (used outside of ObjectBox)
+  int model_relation_external_name(
+    ffi.Pointer<OBX_model> model,
+    ffi.Pointer<ffi.Char> external_name,
+  ) {
+    return _model_relation_external_name(
+      model,
+      external_name,
+    );
+  }
+
+  late final _model_relation_external_namePtr = _lookup<
+      ffi.NativeFunction<
+          obx_err Function(ffi.Pointer<OBX_model>,
+              ffi.Pointer<ffi.Char>)>>('obx_model_relation_external_name');
+  late final _model_relation_external_name =
+      _model_relation_external_namePtr.asFunction<
+          int Function(ffi.Pointer<OBX_model>, ffi.Pointer<ffi.Char>)>();
+
+  /// Augments the previously defined relation with an external type (used outside of ObjectBox)
+  int model_relation_external_type(
+    ffi.Pointer<OBX_model> model,
+    int external_type,
+  ) {
+    return _model_relation_external_type(
+      model,
+      external_type,
+    );
+  }
+
+  late final _model_relation_external_typePtr = _lookup<
+          ffi
+          .NativeFunction<obx_err Function(ffi.Pointer<OBX_model>, ffi.Int32)>>(
+      'obx_model_relation_external_type');
+  late final _model_relation_external_type = _model_relation_external_typePtr
+      .asFunction<int Function(ffi.Pointer<OBX_model>, int)>();
+
   /// Set the highest ever known entity id in the model. Should always be equal to or higher than the
   /// last entity id of the previous version of the model
   void model_last_entity_id(
@@ -765,27 +905,6 @@ class ObjectBoxC {
   late final _model_last_relation_id = _model_last_relation_idPtr
       .asFunction<void Function(ffi.Pointer<OBX_model>, int, int)>();
 
-  /// Set the highest ever known property id in the entity. Should always be equal to or higher than the
-  /// last property id of the previous version of the entity.
-  int model_entity_last_property_id(
-    ffi.Pointer<OBX_model> model,
-    int property_id,
-    int property_uid,
-  ) {
-    return _model_entity_last_property_id(
-      model,
-      property_id,
-      property_uid,
-    );
-  }
-
-  late final _model_entity_last_property_idPtr = _lookup<
-      ffi.NativeFunction<
-          obx_err Function(ffi.Pointer<OBX_model>, obx_schema_id,
-              obx_uid)>>('obx_model_entity_last_property_id');
-  late final _model_entity_last_property_id = _model_entity_last_property_idPtr
-      .asFunction<int Function(ffi.Pointer<OBX_model>, int, int)>();
-
   /// Get the actual bytes from the given OBX_bytes_lazy.
   /// Because of the potential lazy creation of bytes, the given bytes are not const as it may be resolved internally.
   /// For the same reason, this function is not thread-safe, at least for the first call on a OBX_bytes_lazy instance.
@@ -10510,6 +10629,78 @@ abstract class OBXPropertyFlags {
   static const int EXPIRATION_TIME = 65536;
 }
 
+/// A property type of an external system (e.g. another database) that has no default mapping to an ObjectBox type.
+/// External property types numeric values start at 100 to avoid overlaps with ObjectBox's PropertyType.
+/// (And if we ever support one of these as a primary type, we could share the numeric value?)
+abstract class OBXExternalPropertyType {
+  /// Not a real type: represents uninitialized state and can be used for forward compatibility.
+  static const int Unknown = 0;
+
+  /// Representing type: ByteVector
+  /// Encoding: 1:1 binary representation, little endian (16 bytes)
+  static const int Int128 = 100;
+
+  /// Representing type: ByteVector
+  /// Encoding: 1:1 binary representation (16 bytes)
+  static const int Uuid = 102;
+
+  /// IEEE 754 decimal128 type, e.g. supported by MongoDB
+  /// Representing type: ByteVector
+  /// Encoding: 1:1 binary representation (16 bytes)
+  static const int Decimal128 = 103;
+
+  /// A key/value map; e.g. corresponds to a JSON object or a MongoDB document (although not keeping the key order).
+  /// Unlike the Flex type, this must contain a map value (e.g. not a vector or a scalar).
+  /// Representing type: Flex
+  /// Encoding: Flex
+  static const int FlexMap = 107;
+
+  /// A vector (aka list or array) of flexible elements; e.g. corresponds to a JSON array or a MongoDB array.
+  /// Unlike the Flex type, this must contain a vector value (e.g. not a map or a scalar).
+  /// Representing type: Flex
+  /// Encoding: Flex
+  static const int FlexVector = 108;
+
+  /// Placeholder (not yet used) for a JSON document.
+  /// Representing type: String
+  static const int Json = 109;
+
+  /// Placeholder (not yet used) for a BSON document.
+  /// Representing type: ByteVector
+  static const int Bson = 110;
+
+  /// JavaScript source code
+  /// Representing type: String
+  static const int JavaScript = 111;
+
+  /// A vector (array) of Int128 values
+  static const int Int128Vector = 116;
+
+  /// A vector (array) of Int128 values
+  static const int UuidVector = 118;
+
+  /// The 12-byte ObjectId type in MongoDB
+  /// Representing type: ByteVector
+  /// Encoding: 1:1 binary representation (12 bytes)
+  static const int MongoId = 123;
+
+  /// A vector (array) of MongoId values
+  static const int MongoIdVector = 124;
+
+  /// Representing type: Long
+  /// Encoding: Two unsigned 32-bit integers merged into a 64-bit integer.
+  static const int MongoTimestamp = 125;
+
+  /// Representing type: ByteVector
+  /// Encoding: 3 zero bytes (reserved, functions as padding), fourth byte is the sub-type,
+  /// followed by the binary data.
+  static const int MongoBinary = 126;
+
+  /// Representing type: string vector with 2 elements (index 0: pattern, index 1: options)
+  /// Encoding: 1:1 string representation
+  static const int MongoRegex = 127;
+}
+
 class OBX_model extends ffi.Opaque {}
 
 /// Schema entity & property identifiers
@@ -11459,7 +11650,7 @@ typedef obx_dart_closer
 
 const int OBX_VERSION_MAJOR = 4;
 
-const int OBX_VERSION_MINOR = 1;
+const int OBX_VERSION_MINOR = 2;
 
 const int OBX_VERSION_PATCH = 0;
 
diff --git a/objectbox/lib/src/native/model.dart b/objectbox/lib/src/native/model.dart
index e6071a28a..35753f9b9 100644
--- a/objectbox/lib/src/native/model.dart
+++ b/objectbox/lib/src/native/model.dart
@@ -52,6 +52,15 @@ class Model {
 
     if (entity.flags != 0) _check(C.model_entity_flags(_cModel, entity.flags));
 
+    final externalName = entity.externalName?.toNativeUtf8();
+    if (externalName != null) {
+      try {
+        _check(C.model_entity_external_name(_cModel, externalName.cast()));
+      } finally {
+        calloc.free(externalName);
+      }
+    }
+
     // add all properties
     entity.properties.forEach(addProperty);
 
@@ -115,10 +124,34 @@ class Model {
             _cModel, hnswParams.vectorCacheHintSizeKB!));
       }
     }
+
+    final externalType = prop.externalType;
+    if (externalType != null) {
+      _check(C.model_property_external_type(_cModel, externalType));
+    }
+    final externalName = prop.externalName?.toNativeUtf8();
+    if (externalName != null) {
+      try {
+        _check(C.model_property_external_name(_cModel, externalName.cast()));
+      } finally {
+        calloc.free(externalName);
+      }
+    }
   }
 
   void addRelation(ModelRelation rel) {
     _check(C.model_relation(
         _cModel, rel.id.id, rel.id.uid, rel.targetId.id, rel.targetId.uid));
+    if (rel.externalType != null) {
+      _check(C.model_relation_external_type(_cModel, rel.externalType!));
+    }
+    final externalName = rel.externalName?.toNativeUtf8();
+    if (externalName != null) {
+      try {
+        _check(C.model_relation_external_name(_cModel, externalName.cast()));
+      } finally {
+        calloc.free(externalName);
+      }
+    }
   }
 }
diff --git a/objectbox_test/test/box_test.dart b/objectbox_test/test/box_test.dart
index f56b41ad7..90c1f9237 100644
--- a/objectbox_test/test/box_test.dart
+++ b/objectbox_test/test/box_test.dart
@@ -724,6 +724,22 @@ void main() {
     expect(item2.tFloat64List, [-2000.00001, 2000.00001]);
   });
 
+  test('@ExternalType and @ExternalName annotations work correctly', () {
+    // That the database accepts a model with external types and names is tested
+    // implicitly by creating a Store. This test is only a smoke test to verify
+    // the annotated properties and ToMany work without issue.
+    final box = store.box<EntityWithExternalType>();
+    var testObject = EntityWithExternalType([90, 100, 110], [1, 2, 3]);
+    testObject.mongoIdEntities
+        .add(EntityWithExternalType([120, 121, 122], null));
+    final id = box.put(testObject);
+    final item = box.get(id)!;
+    expect(item.id, id);
+    expect(item.mongoId, [90, 100, 110]);
+    expect(item.mongoUuid, [1, 2, 3]);
+    expect(item.mongoIdEntities.first.mongoId, [120, 121, 122]);
+  });
+
   test('.count() works', () {
     expect(box.count(), equals(0));
     box.putMany(simpleItems());
diff --git a/objectbox_test/test/entity.dart b/objectbox_test/test/entity.dart
index 5712476d6..1bfcf3297 100644
--- a/objectbox_test/test/entity.dart
+++ b/objectbox_test/test/entity.dart
@@ -472,6 +472,27 @@ class HnswObject {
   final rel = ToOne<RelatedNamedEntity>();
 }
 
+@Entity()
+@ExternalName(name: 'my-mongo-entity')
+class EntityWithExternalType {
+  @Id()
+  int id = 0;
+
+  @Property(type: PropertyType.byteVector)
+  @ExternalType(type: ExternalPropertyType.mongoId)
+  List<int>? mongoId;
+
+  @ExternalType(type: ExternalPropertyType.uuid)
+  @ExternalName(name: 'my-mongo-uuid')
+  List<int>? mongoUuid;
+
+  @ExternalType(type: ExternalPropertyType.mongoIdVector)
+  @ExternalName(name: 'my-mongo-rel')
+  final mongoIdEntities = ToMany<EntityWithExternalType>();
+
+  EntityWithExternalType(this.mongoId, this.mongoUuid);
+}
+
 @Entity()
 class RelatedNamedEntity {
   @Id()
diff --git a/objectbox_test/test/objectbox-model.json b/objectbox_test/test/objectbox-model.json
index 99635f567..ebb6adf65 100644
--- a/objectbox_test/test/objectbox-model.json
+++ b/objectbox_test/test/objectbox-model.json
@@ -724,11 +724,47 @@
         }
       ],
       "relations": []
+    },
+    {
+      "id": "16:5931645853908059165",
+      "lastPropertyId": "3:7670802129899081197",
+      "name": "EntityWithExternalType",
+      "externalName": "my-mongo-entity",
+      "properties": [
+        {
+          "id": "1:3044824951282217899",
+          "name": "id",
+          "type": 6,
+          "flags": 1
+        },
+        {
+          "id": "2:8057333288729755334",
+          "name": "mongoId",
+          "type": 23,
+          "externalType": 123
+        },
+        {
+          "id": "3:7670802129899081197",
+          "name": "mongoUuid",
+          "type": 27,
+          "externalType": 102,
+          "externalName": "my-mongo-uuid"
+        }
+      ],
+      "relations": [
+        {
+          "id": "2:313640065593441165",
+          "name": "mongoIdEntities",
+          "targetId": "16:5931645853908059165",
+          "externalType": 124,
+          "externalName": "my-mongo-rel"
+        }
+      ]
     }
   ],
-  "lastEntityId": "15:4803284427984871569",
+  "lastEntityId": "16:5931645853908059165",
   "lastIndexId": "23:6649884639373473085",
-  "lastRelationId": "1:2155747579134420981",
+  "lastRelationId": "2:313640065593441165",
   "lastSequenceId": "0:0",
   "modelVersion": 5,
   "modelVersionParserMinimum": 5,
diff --git a/sync_flutter_libs/android/build.gradle b/sync_flutter_libs/android/build.gradle
index 95ae6c0f1..39ec10d25 100644
--- a/sync_flutter_libs/android/build.gradle
+++ b/sync_flutter_libs/android/build.gradle
@@ -52,6 +52,6 @@ android {
         // ObjectBox Android library that includes an ObjectBox C library version compatible with
         // the C API binding of the ObjectBox Dart package.
         // https://central.sonatype.com/search?q=g:io.objectbox%20objectbox-sync-android
-        implementation "io.objectbox:objectbox-sync-android:4.1.0"
+        implementation "io.objectbox:objectbox-sync-android:4.2.0"
     }
 }
diff --git a/sync_flutter_libs/ios/objectbox_sync_flutter_libs.podspec b/sync_flutter_libs/ios/objectbox_sync_flutter_libs.podspec
index d452b7b91..3267a9d1a 100644
--- a/sync_flutter_libs/ios/objectbox_sync_flutter_libs.podspec
+++ b/sync_flutter_libs/ios/objectbox_sync_flutter_libs.podspec
@@ -18,7 +18,7 @@ Pod::Spec.new do |s|
   s.source_files     = 'Classes/**/*'
 
   s.dependency 'Flutter'
-  s.dependency 'ObjectBox', '4.1.0-sync'
+  s.dependency 'ObjectBox', '4.2.0-sync'
 
   # Flutter.framework does not contain a i386 slice.
   s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'i386' }
diff --git a/sync_flutter_libs/linux/CMakeLists.txt b/sync_flutter_libs/linux/CMakeLists.txt
index 4958308b2..246d71b49 100644
--- a/sync_flutter_libs/linux/CMakeLists.txt
+++ b/sync_flutter_libs/linux/CMakeLists.txt
@@ -44,7 +44,7 @@ target_link_libraries(${PLUGIN_NAME} PRIVATE PkgConfig::GTK)
 # ----------------------------------------------------------------------
 # Download and add objectbox-c prebuilt library.
 
-set(OBJECTBOX_VERSION 4.1.0)
+set(OBJECTBOX_VERSION 4.2.0)
 
 set(OBJECTBOX_ARCH ${CMAKE_SYSTEM_PROCESSOR})
 if (${OBJECTBOX_ARCH} MATCHES "x86_64")
diff --git a/sync_flutter_libs/macos/objectbox_sync_flutter_libs.podspec b/sync_flutter_libs/macos/objectbox_sync_flutter_libs.podspec
index 7c39f43e0..eab6f3d23 100644
--- a/sync_flutter_libs/macos/objectbox_sync_flutter_libs.podspec
+++ b/sync_flutter_libs/macos/objectbox_sync_flutter_libs.podspec
@@ -14,7 +14,7 @@ Pod::Spec.new do |s|
   s.source_files     = 'Classes/**/*'
 
   s.dependency 'FlutterMacOS'
-  s.dependency 'ObjectBox', '4.1.0-sync'
+  s.dependency 'ObjectBox', '4.2.0-sync'
 
   s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES' }
   s.swift_version = '5.3'
diff --git a/sync_flutter_libs/windows/CMakeLists.txt b/sync_flutter_libs/windows/CMakeLists.txt
index 75e929653..4fcd94c55 100644
--- a/sync_flutter_libs/windows/CMakeLists.txt
+++ b/sync_flutter_libs/windows/CMakeLists.txt
@@ -50,7 +50,7 @@ set(objectbox_sync_flutter_libs_bundled_libraries
 # ----------------------------------------------------------------------
 # Download and add objectbox-c prebuilt library.
 
-set(OBJECTBOX_VERSION 4.1.0)
+set(OBJECTBOX_VERSION 4.2.0)
 
 set(OBJECTBOX_ARCH ${CMAKE_SYSTEM_PROCESSOR})
 if (${OBJECTBOX_ARCH} MATCHES "AMD64")
diff --git a/tool/common.sh b/tool/common.sh
index e8f41ba0c..171f16379 100755
--- a/tool/common.sh
+++ b/tool/common.sh
@@ -9,11 +9,17 @@ root=$(
 )
 echo "Repo root dir: $root"
 
-# align GNU vs BSD `sed` version handling -i argument
+# macOS includes the BSD version of sed, which uses a different syntax than the
+# GNU version, which these scripts expect. So require users of this script to
+# install gsed.
 if [[ "$OSTYPE" == "darwin"* ]]; then
-  sed="sed -i ''"
+  if ! command -v gsed &>/dev/null; then
+    echo "Error: gsed is required but not installed. Install it, for example using 'brew install gsed'."
+    exit 1
+  fi
+  sed="gsed"
 else
-  sed="sed -i"
+  sed="sed"
 fi
 
 function update() {
@@ -26,5 +32,5 @@ function update() {
   expr=${2}
 
   echo "Updating ${file} - \"${expr}\""
-  $sed "${expr}" "$root/$file"
+  $sed -i "${expr}" "$root/$file"
 }
diff --git a/tool/update-c-binding.sh b/tool/update-c-binding.sh
index c8b3a2bdf..87789a244 100755
--- a/tool/update-c-binding.sh
+++ b/tool/update-c-binding.sh
@@ -5,7 +5,7 @@
 # copies the header files, makes some required modifications
 # and runs the ffigen binding generator on them.
 
-cLibVersion=4.1.0
+cLibVersion=4.2.0
 echo "Downloading C library source files from GitHub..."
 
 # Note: the release archives do not contain objectbox-dart.h, so get the full sources.