Fix RealmObject.hashCode

CHANGELOG.md

@@ -5,6 +5,7 @@
 
 ### Fixed
 * Fixed iteration after `skip` bug ([#1409](https://github.com/realm/realm-dart/issues/1409))
+* Fixed RealmObject not overriding `hashCode`, which would lead to sets of RealmObjects potentially containing duplicates. ([#1418](https://github.com/realm/realm-dart/issues/1418))
 
 ### Compatibility
 * Realm Studio: 13.0.0 or later.

lib/src/native/realm_core.dart

@@ -1490,6 +1490,15 @@ class _RealmCore {
   bool userEquals(User first, User second) => _equals(first.handle, second.handle);
   bool subscriptionEquals(Subscription first, Subscription second) => _equals(first.handle, second.handle);
 
+  int objectGetHashCode(RealmObjectBase value) {
+    final link = realmCore._getObjectAsLink(value);
+
+    var hashCode = -986587137;
+    hashCode = (hashCode * -1521134295) + link.classKey;
+    hashCode = (hashCode * -1521134295) + link.targetKey;
+    return hashCode;
+  }
+
   RealmResultsHandle resultsSnapshot(RealmResults results) {
     final resultsPointer = _realmLib.invokeGetPointer(() => _realmLib.realm_results_snapshot(results.handle._pointer));
     return RealmResultsHandle._(resultsPointer, results.realm.handle);

lib/src/realm_object.dart

@@ -383,9 +383,21 @@ mixin RealmObjectBase on RealmEntity implements RealmObjectBaseMarker, Finalizab
     if (identical(this, other)) return true;
     if (other is! RealmObjectBase) return false;
     if (!isManaged || !other.isManaged) return false;
+
     return realmCore.objectEquals(this, other);
   }
 
+  late final int _managedHashCode = realmCore.objectGetHashCode(this);
+
+  @override
+  int get hashCode {
+    if (!isManaged) {
+      return super.hashCode;
+    }
+
+    return _managedHashCode;
+  }
+
   /// Gets a value indicating whether this object is managed and represents a row in the database.
   ///
   /// If a managed object has been removed from the [Realm], it is no longer valid and accessing properties on it

test/realm_object_test.dart

@@ -18,7 +18,6 @@
 
 // ignore_for_file: unused_local_variable, avoid_relative_lib_imports
 
-import 'dart:io';
 import 'dart:typed_data';
 import 'package:test/test.dart' hide test, throws;
 import '../lib/realm.dart';
@@ -723,4 +722,102 @@ Future<void> main([List<String>? args]) async {
       if (count > 1) fail('Should only receive one event');
     }
   });
+
+  test('RealmObject read deleted object properties', () {
+    var config = Configuration.local([Team.schema, Person.schema]);
+    var realm = getRealm(config);
+
+    var team = Team("TeamOne");
+    realm.write(() => realm.add(team));
+    var teams = realm.all<Team>();
+    var teamBeforeDelete = teams[0];
+    realm.write(() => realm.delete(team));
+    expect(team.isValid, false);
+    expect(teamBeforeDelete.isValid, false);
+    expect(team, teamBeforeDelete);
+    expect(() => team.name, throws<RealmException>("Accessing object of type Team which has been invalidated or deleted"));
+    expect(() => teamBeforeDelete.name, throws<RealmException>("Accessing object of type Team which has been invalidated or deleted"));
+  });
+
+  test('RealmObject.hashCode changes after adding to Realm', () {
+    final config = Configuration.local([Team.schema, Person.schema]);
+    final realm = getRealm(config);
+
+    final team = Team("TeamOne");
+
+    final unmanagedHash = team.hashCode;
+
+    realm.write(() => realm.add(team));
+
+    final managedHash = team.hashCode;
+
+    expect(managedHash, isNot(unmanagedHash));
+    expect(managedHash, equals(team.hashCode));
+  });
+
+  test('RealmObject.hashCode is different for different objects', () {
+    final config = Configuration.local([Team.schema, Person.schema]);
+    final realm = getRealm(config);
+
+    final a = Team("a");
+    final b = Team("b");
+
+    expect(a.hashCode, isNot(b.hashCode));
+
+    realm.write(() {
+      realm.add(a);
+      realm.add(b);
+    });
+
+    expect(a.hashCode, isNot(b.hashCode));
+  });
+
+  test('RealmObject.hashCode is same for equal objects', () {
+    final config = Configuration.local([Team.schema, Person.schema]);
+    final realm = getRealm(config);
+
+    final team = Team("TeamOne");
+
+    realm.write(() {
+      realm.add(team);
+    });
+
+    final teamAgain = realm.all<Team>().first;
+
+    expect(team.hashCode, equals(teamAgain.hashCode));
+  });
+
+  test('RealmObject.hashCode remains stable after deletion', () {
+    final config = Configuration.local([Team.schema, Person.schema]);
+    final realm = getRealm(config);
+
+    final team = Team("TeamOne");
+
+    realm.write(() {
+      realm.add(team);
+    });
+
+    final teamAgain = realm.all<Team>().first;
+
+    final managedHash = team.hashCode;
+
+    realm.write(() => realm.delete(team));
+
+    expect(team.hashCode, equals(managedHash)); // Object that was just deleted shouldn't change its hash code
+    expect(teamAgain.hashCode, equals(managedHash)); // Object that didn't hash its hash code and its row got deleted should still have the same hash code
+  });
+
+  test("RealmObject when added to set doesn't have duplicates", () {
+    final config = Configuration.local([Team.schema, Person.schema]);
+    final realm = getRealm(config);
+
+    realm.write(() {
+      realm.add(Team("TeamOne"));
+    });
+
+    final setOne = realm.all<Team>().toSet();
+    final setTwo = realm.all<Team>().toSet();
+
+    expect(setOne.difference(setTwo).length, 0);
+  });
 }