Allow setting primary keys during migration

CHANGELOG.md

@@ -1,7 +1,21 @@
 ## vNext (TBD)
 
 ### Enhancements
-* None
+* Lifted a limitation that would prevent you from changing the primary key of objects during a migration. It is now possible to do it with both the dynamic and the strongly-typed API:
+  ```csharp
+  var config = new RealmConfiguration
+  {
+    SchemaVersion = 5,
+    MigrationCallback = (migration, oldVersion) =>
+    {
+      // Increment the primary key value of all Foos
+      foreach (var obj in realm.All<Foo>())
+      {
+        obj.Id = obj.Id + 1000;
+      }
+    }
+  }
+  ```
 
 ### Fixed
 * Fixed an issue with xUnit tests that would cause `System.Runtime.InteropServices.SEHException` to be thrown whenever Realm was accessed in a non-async test. (Issue [#1865](https://github.com/realm/realm-dotnet/issues/1865))

Realm/Realm/DatabaseTypes/RealmObjectBase.cs

@@ -224,7 +224,14 @@ protected void SetValueUnique(string propertyName, RealmValue val)
         {
             Debug.Assert(IsManaged, "Object is not managed, but managed access was attempted");
 
-            _objectHandle.SetValueUnique(propertyName, _metadata, val);
+            if (_realm.IsInMigration)
+            {
+                _objectHandle.SetValue(propertyName, _metadata, val, _realm);
+            }
+            else
+            {
+                _objectHandle.SetValueUnique(propertyName, _metadata, val);
+            }
         }
 
         protected internal IList<T> GetListValue<T>(string propertyName)

Realm/Realm/Handles/SharedRealmHandle.cs

@@ -713,7 +713,7 @@ private static bool OnMigration(IntPtr oldRealmPtr, IntPtr newRealmPtr, IntPtr m
             var oldRealm = new Realm(oldRealmHandle, oldConfiguration, RealmSchema.CreateFromObjectStoreSchema(oldSchema));
 
             var newRealmHandle = new UnownedRealmHandle(newRealmPtr);
-            var newRealm = new Realm(newRealmHandle, migration.Configuration, migration.Schema);
+            var newRealm = new Realm(newRealmHandle, migration.Configuration, migration.Schema, isInMigration: true);
 
             var result = migration.Execute(oldRealm, newRealm, migrationSchema);
 

Realm/Realm/Realm.cs

@@ -154,6 +154,7 @@ public static void DeleteRealm(RealmConfigurationBase configuration)
 
         internal readonly SharedRealmHandle SharedRealmHandle;
         internal readonly RealmMetadata Metadata;
+        internal readonly bool IsInMigration;
 
         /// <summary>
         /// Gets an object encompassing the dynamic API for this Realm instance.
@@ -275,9 +276,10 @@ public SubscriptionSet Subscriptions
             }
         }
 
-        internal Realm(SharedRealmHandle sharedRealmHandle, RealmConfigurationBase config, RealmSchema schema, RealmMetadata metadata = null)
+        internal Realm(SharedRealmHandle sharedRealmHandle, RealmConfigurationBase config, RealmSchema schema, RealmMetadata metadata = null, bool isInMigration = false)
         {
             Config = config;
+            IsInMigration = isInMigration;
 
             if (config.EnableCache && sharedRealmHandle.OwnsNativeRealm)
             {
@@ -1189,7 +1191,12 @@ public T ResolveReference<T>(ThreadSafeReference.Object<T> reference)
                 return null;
             }
 
-            return (T)MakeObject(reference.Metadata, objectHandle);
+            if (!Metadata.TryGetValue(reference.Metadata.Schema.Name, out var metadata))
+            {
+                metadata = reference.Metadata;
+            }
+
+            return (T)MakeObject(metadata, objectHandle);
         }
 
         /// <summary>

Tests/Realm.Tests/Database/MigrationTests.cs

@@ -556,5 +556,187 @@ public void Migration_NewRealm_Remove()
             Assert.That(realm2.All<IntPropertyObject>().ToArray().Select(o => o.Int), Is.EqualTo(expected));
             Assert.That(realm2.All<RequiredStringObject>().ToArray().Select(o => int.Parse(o.String)), Is.EqualTo(expected));
         }
+
+        [Test]
+        public void Migration_ChangePrimaryKey_Dynamic()
+        {
+            var oldRealmConfig = new RealmConfiguration(Guid.NewGuid().ToString());
+            using (var oldRealm = GetRealm(oldRealmConfig))
+            {
+                oldRealm.Write(() =>
+                {
+                    oldRealm.Add(new IntPrimaryKeyWithValueObject
+                    {
+                        Id = 123,
+                        StringValue = "123"
+                    });
+                });
+            }
+
+            var newRealmConfig = new RealmConfiguration(oldRealmConfig.DatabasePath)
+            {
+                SchemaVersion = 1,
+                MigrationCallback = (migration, oldSchemaVersion) =>
+                {
+                    var value = (RealmObjectBase)migration.NewRealm.DynamicApi.Find(nameof(IntPrimaryKeyWithValueObject), 123);
+                    value.DynamicApi.Set("_id", 456);
+                }
+            };
+
+            using var realm = GetRealm(newRealmConfig);
+
+            var obj123 = realm.Find<IntPrimaryKeyWithValueObject>(123);
+            var obj456 = realm.Find<IntPrimaryKeyWithValueObject>(456);
+
+            Assert.That(obj123, Is.Null);
+            Assert.That(obj456, Is.Not.Null);
+            Assert.That(obj456.StringValue, Is.EqualTo("123"));
+        }
+
+        [Test]
+        public void Migration_ChangePrimaryKey_Static()
+        {
+            var oldRealmConfig = new RealmConfiguration(Guid.NewGuid().ToString());
+            using (var oldRealm = GetRealm(oldRealmConfig))
+            {
+                oldRealm.Write(() =>
+                {
+                    oldRealm.Add(new IntPrimaryKeyWithValueObject
+                    {
+                        Id = 123,
+                        StringValue = "123"
+                    });
+                });
+            }
+
+            var newRealmConfig = new RealmConfiguration(oldRealmConfig.DatabasePath)
+            {
+                SchemaVersion = 1,
+                MigrationCallback = (migration, oldSchemaVersion) =>
+                {
+                    var value = migration.NewRealm.Find<IntPrimaryKeyWithValueObject>(123);
+                    value.Id = 456;
+                }
+            };
+
+            using var realm = GetRealm(newRealmConfig);
+
+            var obj123 = realm.Find<IntPrimaryKeyWithValueObject>(123);
+            var obj456 = realm.Find<IntPrimaryKeyWithValueObject>(456);
+
+            Assert.That(obj123, Is.Null);
+            Assert.That(obj456, Is.Not.Null);
+            Assert.That(obj456.StringValue, Is.EqualTo("123"));
+        }
+
+        [Test]
+        public void Migration_ChangePrimaryKeyType()
+        {
+            var oldRealmConfig = new RealmConfiguration(Guid.NewGuid().ToString())
+            {
+                Schema = new[] { typeof(ObjectV1) }
+            };
+
+            using (var oldRealm = GetRealm(oldRealmConfig))
+            {
+                oldRealm.Write(() =>
+                {
+                    oldRealm.Add(new ObjectV1
+                    {
+                        Id = 1,
+                        Value = "foo"
+                    });
+
+                    oldRealm.Add(new ObjectV1
+                    {
+                        Id = 2,
+                        Value = "bar"
+                    });
+                });
+            }
+
+            var newRealmConfig = new RealmConfiguration(oldRealmConfig.DatabasePath)
+            {
+                SchemaVersion = 1,
+                Schema = new[] { typeof(ObjectV2) },
+                MigrationCallback = (migration, oldSchemaVersion) =>
+                {
+                    foreach (var oldObj in (IQueryable<RealmObject>)migration.OldRealm.DynamicApi.All("Object"))
+                    {
+                        var newObj = (ObjectV2)migration.NewRealm.ResolveReference(ThreadSafeReference.Create(oldObj));
+                        newObj.Id = oldObj.DynamicApi.Get<int>("Id").ToString();
+                    }
+                }
+            };
+
+            using var realm = GetRealm(newRealmConfig);
+
+            Assert.That(realm.All<ObjectV2>().AsEnumerable().Select(o => o.Value), Is.EquivalentTo(new[] { "foo", "bar" }));
+            Assert.That(realm.All<ObjectV2>().AsEnumerable().Select(o => o.Id), Is.EquivalentTo(new[] { "1", "2" }));
+        }
+
+        [Test]
+        public void Migration_ChangePrimaryKey_WithDuplicates_Throws()
+        {
+            var oldRealmConfig = new RealmConfiguration(Guid.NewGuid().ToString());
+            using (var oldRealm = GetRealm(oldRealmConfig))
+            {
+                oldRealm.Write(() =>
+                {
+                    oldRealm.Add(new IntPrimaryKeyWithValueObject
+                    {
+                        Id = 1,
+                        StringValue = "1"
+                    });
+                    oldRealm.Add(new IntPrimaryKeyWithValueObject
+                    {
+                        Id = 2,
+                        StringValue = "2"
+                    });
+                });
+            }
+
+            var newRealmConfig = new RealmConfiguration(oldRealmConfig.DatabasePath)
+            {
+                SchemaVersion = 1,
+                MigrationCallback = (migration, oldSchemaVersion) =>
+                {
+                    var value = migration.NewRealm.Find<IntPrimaryKeyWithValueObject>(1);
+                    value.Id = 2;
+                }
+            };
+
+            var ex = Assert.Throws<RealmDuplicatePrimaryKeyValueException>(() => GetRealm(newRealmConfig));
+            Assert.That(ex.Message, Does.Contain($"{nameof(IntPrimaryKeyWithValueObject)}._id"));
+
+            // Ensure we haven't messed up the data
+            using var oldRealmAgain = GetRealm(oldRealmConfig);
+
+            var obj1 = oldRealmAgain.Find<IntPrimaryKeyWithValueObject>(1);
+            var obj2 = oldRealmAgain.Find<IntPrimaryKeyWithValueObject>(2);
+
+            Assert.That(obj1.StringValue, Is.EqualTo("1"));
+            Assert.That(obj2.StringValue, Is.EqualTo("2"));
+        }
+
+        [Explicit]
+        [MapTo("Object")]
+        private class ObjectV1 : RealmObject
+        {
+            [PrimaryKey]
+            public int Id { get; set; }
+
+            public string Value { get; set; }
+        }
+
+        [Explicit]
+        [MapTo("Object")]
+        private class ObjectV2 : RealmObject
+        {
+            [PrimaryKey]
+            public string Id { get; set; }
+
+            public string Value { get; set; }
+        }
     }
 }