diff --git a/generator/integration-tests/common.dart b/generator/integration-tests/common.dart
index 7585f6590..848d5db31 100644
--- a/generator/integration-tests/common.dart
+++ b/generator/integration-tests/common.dart
@@ -59,13 +59,18 @@ commonModelTests(ModelDefinition defs, ModelInfo jsonModel) {
         jsonModel.retiredEntityUids);
   });
 
-  // TODO when indexes are available
+// TODO when indexes are available
+// TODO see one-liner in the next lastRelationId test
 //  test('lastIndexId', () {
 //    testLastId(defs.model.lastIndexId, defs.model.entities.map((el) => ...), jsonModel.retiredIndexUids);
 //  });
 
-  // TODO when relations are available
-//  test('lastRelationId', () {
-//    testLastId(defs.model.lastRelationId, defs.model.entities.map((el) => ...), jsonModel.retiredRelationUids);
-//  });
+  test('lastRelationId', () {
+    testLastId(
+        defs.model.lastRelationId,
+        defs.model.entities
+            .map((e) => e.properties.where((p) => p.isRelation))
+            .fold([], (a, b) => a + b).map((e) => e.id),
+        jsonModel.retiredRelationUids);
+  });
 }
diff --git a/generator/lib/src/code_builder.dart b/generator/lib/src/code_builder.dart
index 607c688a7..9359aa235 100644
--- a/generator/lib/src/code_builder.dart
+++ b/generator/lib/src/code_builder.dart
@@ -1,5 +1,6 @@
 import 'dart:async';
 import 'dart:io';
+import 'dart:math';
 import 'dart:convert';
 import 'package:build/build.dart';
 import 'package:glob/glob.dart';
@@ -82,6 +83,7 @@ class CodeBuilder extends Builder {
 
     // merge existing model and annotated model that was just read, then write new final model to file
     merge(model, entities);
+    assignLastPropertyIds(model);
     model.validate();
 
     // write model info
@@ -93,6 +95,20 @@ class CodeBuilder extends Builder {
     return model;
   }
 
+  void assignLastPropertyIds(ModelInfo model) {
+    model.entities.forEach((e) {
+      e.properties.forEach((p) {
+        // if (p.isIndexer) {
+        //   model.lastIndexId = p.id; }else
+        if (p.isToOne) {
+          model.lastIndexId = p.relIndexId;
+        } else if (p.isToMany) {
+          model.lastRelationId = p.relationId;
+        }
+      });
+    });
+  }
+
   void updateCode(
       ModelInfo model, List<String> infoFiles, BuildStep buildStep) async {
     // transform '/lib/path/entity.objectbox.info' to 'path/entity.dart'
@@ -131,6 +147,17 @@ class CodeBuilder extends Builder {
     entities.forEach((entity) => mergeEntity(model, entity));
   }
 
+  int generateUid(int seed, Set<int> prohibited) {
+    final rng = Random(seed + DateTime.now().millisecondsSinceEpoch);
+    for (int i = 0; i < 1000; i++) {
+      var uid = rng.nextInt(1 << 32);
+      uid |= rng.nextInt(1 << 32) << 32;
+      uid &= ~(1 << 63);
+      if (!prohibited.contains(uid)) return uid;
+    }
+    return 0;
+  }
+
   void mergeProperty(ModelEntity entity, ModelProperty prop) {
     final propInModel = entity.findSameProperty(prop);
     if (propInModel == null) {
@@ -140,6 +167,10 @@ class CodeBuilder extends Builder {
       propInModel.name = prop.name;
       propInModel.type = prop.type;
       propInModel.flags = prop.flags;
+      if (prop.type.isRelation) {
+        propInModel.targetEntityName = prop.targetEntityName;
+        propInModel.relIndexId = prop.relIndexId;
+      }
     }
   }
 
@@ -160,6 +191,50 @@ class CodeBuilder extends Builder {
     // here, the entity was found already and entityInModel and readEntity might differ, i.e. conflicts need to be resolved, so merge all properties first
     entity.properties.forEach((p) => mergeProperty(entityInModel, p));
 
+    // one to one relation: get the highest relIndexId.id
+    // TODO Ask: Do we want to repair contiguous ids, if one prop is removed in the middle?
+    var relIndexIdCounter = entityInModel.properties
+        .where((p) => p.isToOne && p.relIndexId != null)
+        .map((p) => p.relIndexId.id)
+        .fold(1, (a, b) => a < b ? b : a);
+
+    // Prohibit reuse of indexUids
+    final avoidSameUidSet = Set<int>()..addAll(modelInfo.retiredIndexUids);
+
+    // one to one relation
+    entityInModel.properties.where((p) => p.isToOne).forEach((p) {
+      if (p.relIndexId == null) {
+        p.relIndexId = IdUid.empty();
+      }
+      if (p.relIndexId.isEmpty) {
+        p.relIndexId.id = relIndexIdCounter++;
+        p.relIndexId.uid = generateUid(entityInModel.id.uid, avoidSameUidSet);
+        avoidSameUidSet.add(p.relIndexId.uid);
+      }
+    });
+
+    // many to many relation
+    var relationIdCounter = entityInModel.properties
+        .where((p) => p.isToMany && p.relationId != null)
+        .map((p) => p.relationId.id)
+        .fold(1, (a, b) => a < b ? b : a);
+
+    final targetEntityMap = <String, IdUid>{};
+    final mapEntityNameToId =
+        modelInfo.entities.forEach((e) => targetEntityMap[e.name] = e.id);
+    entityInModel.properties.where((p) => p.isToMany).forEach((p) {
+      if (p.relationId == null) {
+        p.relationId = IdUid.empty();
+      }
+      if (p.relationId.isEmpty) {
+        p.relationId.id = relationIdCounter++;
+        p.relationId.uid = generateUid(entityInModel.id.uid, avoidSameUidSet);
+        avoidSameUidSet.add(p.relationId.uid);
+      }
+
+      p.targetEntityId = targetEntityMap[p.targetEntityName];
+    });
+
     // then remove all properties not present anymore in readEntity
     entityInModel.properties
         .where((p) => entity.findSameProperty(p) == null)
diff --git a/generator/lib/src/code_chunks.dart b/generator/lib/src/code_chunks.dart
index ca208c779..293921cf2 100644
--- a/generator/lib/src/code_chunks.dart
+++ b/generator/lib/src/code_chunks.dart
@@ -57,6 +57,9 @@ class CodeChunks {
         case OBXPropertyType.String:
           fieldType = "String";
           break;
+        case OBXPropertyType.Relation:
+          fieldType = 'Relation';
+          break;
         float:
         case OBXPropertyType.Double:
           fieldType = "Double";
@@ -80,8 +83,11 @@ class CodeChunks {
               "Unsupported property type (${prop.type}): ${entity.name}.${name}");
       }
 
+      final relationTypeGenericParam =
+          prop.type == OBXPropertyType.Relation ? '<${prop.targetEntityName}>' : '';
+
       ret.add("""
-        static final ${name} = Query${fieldType}Property(entityId:${entity.id.id}, propertyId:${prop.id.id}, obxType:${prop.type});
+        static final ${name} = Query${fieldType}Property$relationTypeGenericParam(entityId:${entity.id.id}, propertyId:${prop.id.id}, obxType:${prop.type});
         """);
     }
     return ret.join();
diff --git a/generator/lib/src/entity_resolver.dart b/generator/lib/src/entity_resolver.dart
index 7e866c0e6..fc0d5358a 100644
--- a/generator/lib/src/entity_resolver.dart
+++ b/generator/lib/src/entity_resolver.dart
@@ -2,6 +2,7 @@ import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/type.dart';
 import 'package:build/build.dart';
 import 'package:objectbox/objectbox.dart' as obx;
 import 'package:objectbox/src/bindings/constants.dart';
@@ -17,7 +18,7 @@ class EntityResolver extends Builder {
     '.dart': [suffix]
   };
 
-  final _annotationChecker = const TypeChecker.fromRuntime(obx.Entity);
+  final _entityChecker = const TypeChecker.fromRuntime(obx.Entity);
   final _propertyChecker = const TypeChecker.fromRuntime(obx.Property);
   final _idChecker = const TypeChecker.fromRuntime(obx.Id);
   final _transientChecker = const TypeChecker.fromRuntime(obx.Transient);
@@ -30,9 +31,13 @@ class EntityResolver extends Builder {
 
     // generate for all entities
     final entities = <Map<String, dynamic>>[];
-    for (var annotatedEl in libReader.annotatedWith(_annotationChecker)) {
-      entities.add(generateForAnnotatedElement(
-              annotatedEl.element, annotatedEl.annotation)
+    final annotatedWithEntity = libReader.annotatedWith(_entityChecker);
+    final entityNames = annotatedWithEntity.map((a) => a.element.name).toSet();
+    final entityNamesAsList =
+        annotatedWithEntity.map((a) => 'List<${a.element.name}>').toSet();
+    for (var annotatedEl in annotatedWithEntity) {
+      entities.add(generateForAnnotatedElement(annotatedEl.element,
+              annotatedEl.annotation, entityNames, entityNamesAsList)
           .toMap());
     }
 
@@ -44,7 +49,10 @@ class EntityResolver extends Builder {
   }
 
   ModelEntity generateForAnnotatedElement(
-      Element elementBare, ConstantReader annotation) {
+      Element elementBare,
+      ConstantReader annotation,
+      Set<String> relatableEntityNames,
+      Set<String> relatableEntityNamesAsList) {
     if (elementBare is! ClassElement) {
       throw InvalidGenerationSourceError(
           "in target ${elementBare.name}: annotated element isn't a class");
@@ -70,6 +78,7 @@ class EntityResolver extends Builder {
 
       int fieldType, flags = 0;
       int propUid;
+      final dartTypeString = f.type.toString().replaceAll('*', '');
 
       if (_idChecker.hasAnnotationOfExact(f)) {
         if (hasIdProperty) {
@@ -96,7 +105,7 @@ class EntityResolver extends Builder {
       }
 
       if (fieldType == null) {
-        var fieldTypeDart = f.type;
+        final fieldTypeDart = f.type;
 
         if (fieldTypeDart.isDartCoreInt) {
           // dart: 8 bytes
@@ -112,6 +121,9 @@ class EntityResolver extends Builder {
           // dart: 8 bytes
           // ob: 8 bytes
           fieldType = OBXPropertyType.Double;
+        } else if (areRelated(
+            dartTypeString, relatableEntityNames, relatableEntityNamesAsList)) {
+          fieldType = OBXPropertyType.Relation;
         } else {
           log.warning(
               "  skipping property '${f.name}' in entity '${element.name}', as it has the unsupported type '${fieldTypeDart.toString()}'");
@@ -120,8 +132,20 @@ class EntityResolver extends Builder {
       }
 
       // create property (do not use readEntity.createProperty in order to avoid generating new ids)
-      final prop =
-          ModelProperty(IdUid.empty(), f.name, fieldType, flags, readEntity);
+      final isRelation = fieldType == OBXPropertyType.Relation;
+
+      // setup relations
+      final isToOne =
+          isRelation && areRelated(dartTypeString, relatableEntityNames);
+      final isToMany =
+          isRelation && areRelated(dartTypeString, relatableEntityNamesAsList);
+      final prop = ModelProperty(
+          IdUid.empty(), f.name, fieldType, flags, readEntity,
+          targetEntityName: isRelation ? dartTypeString : null,
+          relIndexId: isToOne ? IdUid.empty() : null,
+          relationId: isToMany ? IdUid.empty() : null,
+          targetEntityId: isToMany ? IdUid.empty() : null);
+
       if (propUid != null) prop.id.uid = propUid;
       readEntity.properties.add(prop);
 
@@ -137,4 +161,7 @@ class EntityResolver extends Builder {
 
     return readEntity;
   }
+
+  bool areRelated(String typeString, Set<String> s1, [Set<String> s2]) =>
+      s1.contains(typeString) || (s2 != null && s2.contains(typeString));
 }
diff --git a/generator/pubspec.yaml b/generator/pubspec.yaml
index ee1b2949f..14c0e8308 100644
--- a/generator/pubspec.yaml
+++ b/generator/pubspec.yaml
@@ -5,7 +5,7 @@ homepage: https://objectbox.io
 description: ObjectBox binding code generator - finds annotated entities and adds them to the ObjectBox DB model.
 
 environment:
-  sdk: ">=2.5.0 <3.0.0"
+  sdk: ">=2.6.0 <3.0.0"
 
 dependencies:
   objectbox: 0.8.0
diff --git a/lib/objectbox.dart b/lib/objectbox.dart
index e3b693bcf..b66ae27f7 100644
--- a/lib/objectbox.dart
+++ b/lib/objectbox.dart
@@ -12,3 +12,4 @@ export 'src/model.dart';
 export 'src/modelinfo/index.dart';
 export 'src/query/query.dart';
 export 'src/store.dart';
+export 'src/util.dart';
diff --git a/lib/src/bindings/bindings.dart b/lib/src/bindings/bindings.dart
index 16d852586..1dacf6bab 100644
--- a/lib/src/bindings/bindings.dart
+++ b/lib/src/bindings/bindings.dart
@@ -46,10 +46,20 @@ class _ObjectBoxBindings {
   int Function(Pointer<Void> model, Pointer<Utf8> name, int type,
       int property_id, int property_uid) obx_model_property;
   int Function(Pointer<Void> model, int flags) obx_model_property_flags;
+  int Function(Pointer<Void> model, int index_id, int index_uid)
+      obx_model_property_index_id;
   int Function(Pointer<Void> model, int property_id, int property_uid)
       obx_model_entity_last_property_id;
-  int Function(Pointer<Void> model, int entity_id, int entity_uid)
+  void Function(Pointer<Void> model, int entity_id, int entity_uid)
       obx_model_last_entity_id;
+  void Function(Pointer<Void> model, int entity_id, int index_uid)
+      obx_model_last_index_id;
+  int Function(Pointer<Void> model, Pointer<Utf8> target_entity, int entity_id,
+      int entity_uid) obx_model_property_relation;
+  int Function(Pointer<Void> model, int relation_id, int relation_uid,
+      int target_id, int target_uid) obx_model_relation;
+  void Function(Pointer<Void> model, int relation_id, int relation_uid)
+      obx_model_last_relation_id;
 
   // object store management
   Pointer<Void> Function() obx_opt;
@@ -61,6 +71,7 @@ class _ObjectBoxBindings {
   void Function(Pointer<Void> opt) obx_opt_free;
   Pointer<Void> Function(Pointer<Void> opt) obx_store_open;
   int Function(Pointer<Void> store) obx_store_close;
+  int Function(Pointer<Void> store, int flags) obx_store_debug_flags;
 
   // transactions
   Pointer<Void> Function(Pointer<Void> store) obx_txn_write;
@@ -109,6 +120,13 @@ class _ObjectBoxBindings {
       obx_box_count;
   int Function(Pointer<Void> box, Pointer<Uint8> is_empty) obx_box_is_empty;
 
+  // box relations
+  int Function(Pointer<Void> box, int relation_id, int source_id, int target_id)
+      obx_box_rel_put, obx_box_rel_remove;
+
+  Pointer<OBX_id_array> Function(Pointer<Void> box, int relation_id, int id)
+      obx_box_rel_get_ids, obx_box_rel_get_backlink_ids;
+
   // query builder
   obx_query_builder_dart_t obx_qb_create;
   obx_qb_close_dart_t obx_qb_close;
@@ -155,6 +173,18 @@ class _ObjectBoxBindings {
 
   obx_qb_order_dart_t obx_qb_order;
 
+  Pointer<Void> Function(Pointer<Void> builder, int property_id)
+      obx_qb_link_property;
+  Pointer<Void> Function(
+          Pointer<Void> builder, int source_entity_id, int source_property_id)
+      obx_qb_backlink_property;
+  Pointer<Void> Function(Pointer<Void> builder, int relation_id)
+      obx_qb_link_standalone;
+  Pointer<Void> Function(Pointer<Void> builder, int relation_id)
+      obx_qb_backlink_standalone;
+  Pointer<Void> Function(Pointer<Void> builder, int linked_entity_id,
+      int begin_property_id, int end_property_id) obx_qb_link_time;
+
   // query
   obx_query_t obx_query_create;
   obx_query_close_dart_t obx_query_close;
@@ -299,6 +329,9 @@ class _ObjectBoxBindings {
         _fn<obx_model_entity_native_t>('obx_model_entity').asFunction();
     obx_model_property =
         _fn<obx_model_property_native_t>('obx_model_property').asFunction();
+    obx_model_property_index_id =
+        _fn<obx_model_property_index_id_native_t>('obx_model_property_index_id')
+            .asFunction();
     obx_model_property_flags =
         _fn<obx_model_property_flags_native_t>('obx_model_property_flags')
             .asFunction();
@@ -309,6 +342,17 @@ class _ObjectBoxBindings {
     obx_model_last_entity_id =
         _fn<obx_model_last_entity_id_native_t>('obx_model_last_entity_id')
             .asFunction();
+    obx_model_last_index_id =
+        _fn<obx_model_last_index_id_native_t>('obx_model_last_index_id')
+            .asFunction();
+    obx_model_relation =
+        _fn<obx_model_relation_native_t>('obx_model_relation').asFunction();
+    obx_model_property_relation =
+        _fn<obx_model_property_relation_native_t>('obx_model_property_relation')
+            .asFunction();
+    obx_model_last_relation_id =
+        _fn<obx_model_last_relation_id_native_t>('obx_model_last_relation_id')
+            .asFunction();
 
     // object store management
     obx_opt = _fn<obx_opt_native_t>('obx_opt').asFunction();
@@ -326,6 +370,9 @@ class _ObjectBoxBindings {
         _fn<obx_store_open_native_t>('obx_store_open').asFunction();
     obx_store_close =
         _fn<obx_store_close_native_t>('obx_store_close').asFunction();
+    obx_store_debug_flags =
+        _fn<obx_store_debug_flags_native_t>('obx_store_debug_flags')
+            .asFunction();
 
     // transactions
     obx_txn_write = _fn<obx_txn_write_native_t>('obx_txn_write').asFunction();
@@ -372,6 +419,17 @@ class _ObjectBoxBindings {
     obx_box_is_empty =
         _fn<obx_box_is_empty_native_t>('obx_box_is_empty').asFunction();
 
+    // box relations
+    obx_box_rel_put =
+        _fn<obx_box_rel_put_native_t>('obx_box_rel_put').asFunction();
+    obx_box_rel_remove =
+        _fn<obx_box_rel_remove_native_t>('obx_box_rel_remove').asFunction();
+    obx_box_rel_get_ids =
+        _fn<obx_box_rel_get_ids_native_t>('obx_box_rel_get_ids').asFunction();
+    obx_box_rel_get_backlink_ids = _fn<obx_box_rel_get_backlink_ids_native_t>(
+            'obx_box_rel_get_backlink_ids')
+        .asFunction();
+
     // query builder
     obx_qb_create =
         _fn<obx_query_builder_native_t>('obx_query_builder').asFunction();
@@ -487,6 +545,20 @@ class _ObjectBoxBindings {
 
     obx_qb_order = _fn<obx_qb_order_native_t>('obx_qb_order').asFunction();
 
+    obx_qb_link_property =
+        _fn<obx_qb_link_property_native_t>('obx_qb_link_property').asFunction();
+    obx_qb_backlink_property =
+        _fn<obx_qb_backlink_property_native_t>('obx_qb_backlink_property')
+            .asFunction();
+    obx_qb_link_standalone =
+        _fn<obx_qb_link_standalone_native_t>('obx_qb_link_standalone')
+            .asFunction();
+    obx_qb_backlink_standalone =
+        _fn<obx_qb_backlink_standalone_native_t>('obx_qb_backlink_standalone')
+            .asFunction();
+    obx_qb_link_time =
+        _fn<obx_qb_link_time_native_t>('obx_qb_link_time').asFunction();
+
     // query
     obx_query_create = _fn<obx_query_t>('obx_query').asFunction();
     obx_query_close =
diff --git a/lib/src/bindings/constants.dart b/lib/src/bindings/constants.dart
index 741f53ac1..0f292e2af 100644
--- a/lib/src/bindings/constants.dart
+++ b/lib/src/bindings/constants.dart
@@ -91,3 +91,11 @@ class OBXError {
   /// A requested schema object (e.g. entity or property) was not found in the schema
   static const int OBX_ERROR_SCHEMA_OBJECT_NOT_FOUND = 10503;
 }
+
+class OBXDebugFlags {
+  static const int LOG_TRANSACTIONS_READ = 1;
+  static const int LOG_TRANSACTIONS_WRITE = 2;
+  static const int LOG_QUERIES = 4;
+  static const int LOG_QUERY_PARAMETERS = 8;
+  static const int LOG_ASYNC_QUEUE = 16;
+}
diff --git a/lib/src/bindings/signatures.dart b/lib/src/bindings/signatures.dart
index a0bbf70f8..a2f6786e8 100644
--- a/lib/src/bindings/signatures.dart
+++ b/lib/src/bindings/signatures.dart
@@ -35,12 +35,29 @@ typedef obx_model_entity_native_t = Int32 Function(Pointer<Void> model,
     Pointer<Utf8> name, Uint32 entity_id, Uint64 entity_uid);
 typedef obx_model_property_native_t = Int32 Function(Pointer<Void> model,
     Pointer<Utf8> name, Uint32 type, Uint32 property_id, Uint64 property_uid);
+typedef obx_model_property_index_id_native_t = Int32 Function(
+    Pointer<Void> model, Uint32 index_id, Uint64 index_uid);
 typedef obx_model_property_flags_native_t = Int32 Function(
     Pointer<Void> model, Uint32 flags);
 typedef obx_model_entity_last_property_id_native_t = Int32 Function(
     Pointer<Void> model, Uint32 property_id, Uint64 property_uid);
-typedef obx_model_last_entity_id_native_t = Int32 Function(
+typedef obx_model_last_entity_id_native_t = Void Function(
     Pointer<Void> model, Uint32 entity_id, Uint64 entity_uid);
+typedef obx_model_last_index_id_native_t = Void Function(
+    Pointer<Void> model, Uint32 entity_id, Uint64 index_uid);
+typedef obx_model_property_relation_native_t = Int32 Function(
+    Pointer<Void> model,
+    Pointer<Utf8> target_entity,
+    Uint32 entity_id,
+    Uint64 entity_uid);
+typedef obx_model_relation_native_t = Int32 Function(
+    Pointer<Void> model,
+    Uint32 relation_id,
+    Uint64 relation_uid,
+    Uint32 target_id,
+    Uint64 target_uid);
+typedef obx_model_last_relation_id_native_t = Void Function(
+    Pointer<Void> model, Uint32 relation_id, Uint64 relation_uid);
 
 // object store management
 typedef obx_opt_native_t = Pointer<Void> Function();
@@ -56,6 +73,8 @@ typedef obx_opt_model_native_t = Int32 Function(
     Pointer<Void> opt, Pointer<Void> model);
 typedef obx_store_open_native_t = Pointer<Void> Function(Pointer<Void> opt);
 typedef obx_store_close_native_t = Int32 Function(Pointer<Void> store);
+typedef obx_store_debug_flags_native_t = Int32 Function(
+    Pointer<Void> store, Int32 flags);
 
 // transactions
 typedef obx_txn_write_native_t = Pointer<Void> Function(Pointer<Void> store);
@@ -106,6 +125,15 @@ typedef obx_box_count_native_t = Int32 Function(
 typedef obx_box_is_empty_native_t = Int32 Function(
     Pointer<Void> box, Pointer<Uint8> is_empty);
 
+typedef obx_box_rel_put_native_t = Int32 Function(
+    Pointer<Void> box, Uint32 relation_id, Uint64 source_id, Uint64 target_id);
+typedef obx_box_rel_remove_native_t = Int32 Function(
+    Pointer<Void> box, Uint32 relation_id, Uint64 source_id, Uint64 target_id);
+typedef obx_box_rel_get_ids_native_t = Pointer<OBX_id_array> Function(
+    Pointer<Void> box, Uint32 relation_id, Uint64 id);
+typedef obx_box_rel_get_backlink_ids_native_t = Pointer<OBX_id_array> Function(
+    Pointer<Void> box, Uint32 relation_id, Uint64 id);
+
 // no typedef for non-functions yet, see https://github.com/dart-lang/language/issues/65
 // typedef obx_err = Int32
 // typedef Pointer<Int8> -> char[]
@@ -180,6 +208,20 @@ typedef obx_qb_order_native_t = Int32 Function(
 typedef obx_qb_order_dart_t = int Function(
     Pointer<Void> builder, int property_id, int flags);
 
+typedef obx_qb_link_property_native_t = Pointer<Void> Function(
+    Pointer<Void> builder, Uint32 property_id);
+typedef obx_qb_backlink_property_native_t = Pointer<Void> Function(
+    Pointer<Void> builder, Uint32 source_entity_id, Uint32 source_property_id);
+typedef obx_qb_link_standalone_native_t = Pointer<Void> Function(
+    Pointer<Void> builder, Uint32 relation_id);
+typedef obx_qb_backlink_standalone_native_t = Pointer<Void> Function(
+    Pointer<Void> builder, Uint32 relation_id);
+typedef obx_qb_link_time_native_t = Pointer<Void> Function(
+    Pointer<Void> builder,
+    Uint32 linked_entity_id,
+    Uint32 begin_property_id,
+    Uint32 end_property_id);
+
 // query
 
 typedef obx_query_t = Pointer<Void> Function(Pointer<Void> builder);
diff --git a/lib/src/model.dart b/lib/src/model.dart
index e6ababf2b..3fc595345 100644
--- a/lib/src/model.dart
+++ b/lib/src/model.dart
@@ -21,6 +21,16 @@ class Model {
       // set last entity id
       bindings.obx_model_last_entity_id(
           _cModel, model.lastEntityId.id, model.lastEntityId.uid);
+
+      if (model.lastRelationId != null) {
+        bindings.obx_model_last_relation_id(
+            _cModel, model.lastRelationId.id, model.lastRelationId.uid);
+      }
+
+      if (model.lastIndexId != null) {
+        bindings.obx_model_last_index_id(
+            _cModel, model.lastIndexId.id, model.lastIndexId.uid);
+      }
     } catch (e) {
       bindings.obx_model_free(_cModel);
       _cModel = null;
@@ -55,16 +65,32 @@ class Model {
   }
 
   void addProperty(ModelProperty prop) {
-    var name = Utf8.toUtf8(prop.name);
+    final name = Utf8.toUtf8(prop.name);
     try {
       _check(bindings.obx_model_property(
           _cModel, name, prop.type, prop.id.id, prop.id.uid));
+
+      if (prop.flags != 0) {
+        _check(bindings.obx_model_property_flags(_cModel, prop.flags));
+      }
+
+      if (prop.isToOne) {
+        final targetEntityName = Utf8.toUtf8(prop.targetEntityName);
+
+        _check(bindings.obx_model_property_relation(_cModel, targetEntityName,
+            prop.relIndexId.id, prop.relIndexId.uid));
+
+        free(targetEntityName);
+      } else if (prop.isToMany) {
+        _check(bindings.obx_model_relation(
+            _cModel,
+            prop.relationId.id,
+            prop.relationId.uid,
+            prop.targetEntityId.id,
+            prop.targetEntityId.uid));
+      }
     } finally {
       free(name);
     }
-
-    if (prop.flags != 0) {
-      _check(bindings.obx_model_property_flags(_cModel, prop.flags));
-    }
   }
 }
diff --git a/lib/src/modelinfo/iduid.dart b/lib/src/modelinfo/iduid.dart
index 94a2a3ce6..822ef0eba 100644
--- a/lib/src/modelinfo/iduid.dart
+++ b/lib/src/modelinfo/iduid.dart
@@ -49,6 +49,10 @@ class IdUid {
 
   int get uid => _uid;
 
+  bool get isEmpty {
+    return _id == 0 && _uid == 0;
+  }
+
   @override
   String toString() => '$_id:$_uid';
 }
diff --git a/lib/src/modelinfo/modelentity.dart b/lib/src/modelinfo/modelentity.dart
index c7240cd44..ccc73204b 100644
--- a/lib/src/modelinfo/modelentity.dart
+++ b/lib/src/modelinfo/modelentity.dart
@@ -128,6 +128,9 @@ class ModelEntity {
     final modelProp = createProperty(prop.name, prop.id.uid);
     modelProp.type = prop.type;
     modelProp.flags = prop.flags;
+
+    _hasRelations |= modelProp.isRelation;
+
     return modelProp;
   }
 
@@ -138,8 +141,13 @@ class ModelEntity {
       throw Exception(
           "cannot remove property '${prop.name}' with id ${prop.id.toString()}: not found");
     }
+
     properties = properties.where((p) => p != foundProp).toList();
-    model.retiredPropertyUids.add(prop.id.uid);
+    if (prop.type.isRelation) {
+      model.retiredRelationUids.add(prop.id.uid);
+    } else {
+      model.retiredPropertyUids.add(prop.id.uid);
+    }
   }
 
   bool containsUid(int searched) {
@@ -150,4 +158,7 @@ class ModelEntity {
     }
     return false;
   }
+
+  bool _hasRelations = false;
+  bool get hasRelations => _hasRelations;
 }
diff --git a/lib/src/modelinfo/modelinfo.dart b/lib/src/modelinfo/modelinfo.dart
index 3b42ea895..2a5bc0a99 100644
--- a/lib/src/modelinfo/modelinfo.dart
+++ b/lib/src/modelinfo/modelinfo.dart
@@ -199,7 +199,18 @@ class ModelInfo {
     }
     entities = entities.where((p) => p != foundEntity).toList();
     retiredEntityUids.add(entity.id.uid);
-    entity.properties.forEach((prop) => retiredPropertyUids.add(prop.id.uid));
+
+    entity.properties.forEach((prop) {
+      if (prop.isRelation) {
+        if (prop.targetEntityName.contains('<')) {
+          retiredRelationUids.add(prop.relationId.uid);
+        } else {
+          retiredIndexUids.add(prop.relIndexId.uid);
+        }
+      }
+      // if (prop.isIndexer) { retiredIndexUids.add(prop.indexId.uid); }
+      retiredPropertyUids.add(prop.id.uid);
+    });
   }
 
   int generateUid() {
diff --git a/lib/src/modelinfo/modelproperty.dart b/lib/src/modelinfo/modelproperty.dart
index 717014750..764cd88c4 100644
--- a/lib/src/modelinfo/modelproperty.dart
+++ b/lib/src/modelinfo/modelproperty.dart
@@ -1,3 +1,5 @@
+import 'package:objectbox/src/bindings/constants.dart';
+
 import 'modelentity.dart';
 import 'iduid.dart';
 
@@ -7,8 +9,14 @@ class ModelProperty {
   String name;
   int type, flags;
   ModelEntity entity;
+  String targetEntityName;
+  IdUid relIndexId, relationId, targetEntityId;
 
-  ModelProperty(this.id, this.name, this.type, this.flags, this.entity) {
+  ModelProperty(this.id, this.name, this.type, this.flags, this.entity,
+      {this.targetEntityName,
+      this.relIndexId,
+      this.relationId,
+      this.targetEntityId}) {
     validate();
   }
 
@@ -18,6 +26,22 @@ class ModelProperty {
     name = data['name'];
     type = data['type'];
     flags = data.containsKey('flags') ? data['flags'] : 0;
+
+    // relations
+    targetEntityName =
+        data.containsKey('targetEntityName') ? data['targetEntityName'] : null;
+    relIndexId = data.containsKey('relIndexId')
+        ? IdUid.fromString(data['relIndexId'])
+        : null;
+
+    relationId = data.containsKey('relationId')
+        ? IdUid.fromString(data['relationId'])
+        : null;
+
+    targetEntityId = data.containsKey('targetEntityId')
+        ? IdUid.fromString(data['targetEntityId'])
+        : null;
+
     if (check) validate();
   }
 
@@ -35,6 +59,18 @@ class ModelProperty {
     ret['id'] = id.toString();
     ret['name'] = name;
     ret['type'] = type;
+    if (targetEntityName != null) {
+      ret['targetEntityName'] = targetEntityName;
+    }
+    if (relIndexId != null) {
+      ret['relIndexId'] = relIndexId.toString();
+    }
+    if (targetEntityId != null) {
+      ret['targetEntityId'] = targetEntityId.toString();
+    }
+    if (relationId != null) {
+      ret['relationId'] = relationId.toString();
+    }
     if (flags != 0) ret['flags'] = flags;
     return ret;
   }
@@ -42,4 +78,16 @@ class ModelProperty {
   bool containsUid(int searched) {
     return id.uid == searched;
   }
+
+  bool get isRelation => OBXPropertyType.Relation == type;
+  bool get isToOne => isRelation && !targetEntityName.contains('<');
+  bool get isToMany => isRelation && targetEntityName.contains('<');
+  // bool get isIndexer => [
+  //       OBXPropertyFlag.INDEXED,
+  //       OBXPropertyFlag.UNIQUE,
+  //       OBXPropertyFlag.INDEX_PARTIAL_SKIP_NULL,
+  //       OBXPropertyFlag.INDEX_PARTIAL_SKIP_ZERO,
+  //       OBXPropertyFlag.INDEX_HASH,
+  //       OBXPropertyFlag.INDEX_HASH64
+  //     ].any((i) => (i & flags) == i);
 }
diff --git a/lib/src/query/query.dart b/lib/src/query/query.dart
index cb2dc6f8b..6e1287134 100644
--- a/lib/src/query/query.dart
+++ b/lib/src/query/query.dart
@@ -225,6 +225,11 @@ class QueryBooleanProperty extends QueryProperty {
 // Condition operator ==(bool p) => equals(p); // see issue #43
 }
 
+class QueryRelationProperty<Target> extends QueryProperty {
+  QueryRelationProperty({int entityId, int propertyId, int obxType})
+      : super(entityId, propertyId, obxType);
+}
+
 enum ConditionOp {
   isNull,
   notNull,
diff --git a/lib/src/store.dart b/lib/src/store.dart
index 95ef13bcf..deb710bc2 100644
--- a/lib/src/store.dart
+++ b/lib/src/store.dart
@@ -34,7 +34,11 @@ class Store {
   ///
   /// See our examples for more details.
   Store(this.defs,
-      {String directory, int maxDBSizeInKB, int fileMode, int maxReaders}) {
+      {String directory,
+      int maxDBSizeInKB,
+      int fileMode,
+      int maxReaders,
+      int debugFlags = 0}) {
     var model = Model(defs.model);
 
     var opt = bindings.obx_opt();
@@ -64,6 +68,9 @@ class Store {
       rethrow;
     }
     _cStore = bindings.obx_store_open(opt);
+    if (debugFlags != 0) {
+      checkObx(bindings.obx_store_debug_flags(_cStore, debugFlags));
+    }
 
     try {
       checkObxPtr(_cStore, 'failed to create store');
diff --git a/lib/src/util.dart b/lib/src/util.dart
index 24fd40d7f..c7bc53cbf 100644
--- a/lib/src/util.dart
+++ b/lib/src/util.dart
@@ -1,2 +1,8 @@
+import 'package:objectbox/src/bindings/constants.dart';
+
 bool listContains<T>(List<T> list, T item) =>
     list.indexWhere((x) => x == item) != -1;
+
+extension PropertyType on int {
+  bool get isRelation => this == OBXPropertyType.Relation;
+}
diff --git a/test/entity.dart b/test/entity.dart
index aaaeef2d4..e79a17ea2 100644
--- a/test/entity.dart
+++ b/test/entity.dart
@@ -64,3 +64,27 @@ class TestEntity {
     disregard = 1;
   }
 }
+
+@Entity()
+class RelatedEntityA {
+  @Id()
+  int id;
+
+  int tInt;
+  bool tBool;
+  RelatedEntityB relB;
+
+  RelatedEntityA({this.id, this.tInt, this.tBool, this.relB});
+}
+
+@Entity()
+class RelatedEntityB {
+  @Id()
+  int id;
+
+  String tString;
+  double tDouble;
+  List<TestEntity> listTestEntity;
+
+  RelatedEntityB({this.id, this.tString, this.tDouble, this.listTestEntity});
+}