CSHARP-5587: FindOneAndUpdate should insert correct discriminator value on upsert

src/MongoDB.Driver/FilteredMongoCollectionBase.cs

@@ -304,22 +304,22 @@ public override Task<IAsyncCursor<TItem>> DistinctManyAsync<TItem>(IClientSessio
 
         public override TProjection FindOneAndUpdate<TProjection>(FilterDefinition<TDocument> filter, UpdateDefinition<TDocument> update, FindOneAndUpdateOptions<TDocument, TProjection> options = null, CancellationToken cancellationToken = default(CancellationToken))
         {
-            return _wrappedCollection.FindOneAndUpdate(CombineFilters(filter), update, options, cancellationToken);
+            return _wrappedCollection.FindOneAndUpdate(CombineFilters(filter), AdjustUpdateDefinition(update, options.IsUpsert), options, cancellationToken);
         }
 
         public override TProjection FindOneAndUpdate<TProjection>(IClientSessionHandle session, FilterDefinition<TDocument> filter, UpdateDefinition<TDocument> update, FindOneAndUpdateOptions<TDocument, TProjection> options = null, CancellationToken cancellationToken = default(CancellationToken))
         {
-            return _wrappedCollection.FindOneAndUpdate(session, CombineFilters(filter), update, options, cancellationToken);
+            return _wrappedCollection.FindOneAndUpdate(session, CombineFilters(filter), AdjustUpdateDefinition(update, options.IsUpsert), options, cancellationToken);
         }
 
         public override Task<TProjection> FindOneAndUpdateAsync<TProjection>(FilterDefinition<TDocument> filter, UpdateDefinition<TDocument> update, FindOneAndUpdateOptions<TDocument, TProjection> options = null, CancellationToken cancellationToken = default(CancellationToken))
         {
-            return _wrappedCollection.FindOneAndUpdateAsync(CombineFilters(filter), update, options, cancellationToken);
+            return _wrappedCollection.FindOneAndUpdateAsync(CombineFilters(filter), AdjustUpdateDefinition(update, options.IsUpsert), options, cancellationToken);
         }
 
         public override Task<TProjection> FindOneAndUpdateAsync<TProjection>(IClientSessionHandle session, FilterDefinition<TDocument> filter, UpdateDefinition<TDocument> update, FindOneAndUpdateOptions<TDocument, TProjection> options = null, CancellationToken cancellationToken = default(CancellationToken))
         {
-            return _wrappedCollection.FindOneAndUpdateAsync(session, CombineFilters(filter), update, options, cancellationToken);
+            return _wrappedCollection.FindOneAndUpdateAsync(session, CombineFilters(filter), AdjustUpdateDefinition(update, options.IsUpsert), options, cancellationToken);
         }
 
         [Obsolete("Use Aggregation pipeline instead.")]

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp5587Tests.cs

@@ -0,0 +1,118 @@
+/* Copyright 2010-present MongoDB Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using MongoDB.Driver.TestHelpers;
+using FluentAssertions;
+using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Bson.Serialization.Serializers;
+using MongoDB.Driver.Linq;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3Implementation.Jira;
+
+public class CSharp5587Tests : LinqIntegrationTest<CSharp5587Tests.ClassFixture>
+{
+    public CSharp5587Tests(ClassFixture fixture)
+        : base(fixture)
+    {
+    }
+
+    [Fact]
+    public void FindOneAndUpdate_should_use_correct_discriminator()
+    {
+        var collection = Fixture.Collection;
+
+        var lion1 = new Lion { Id = 1, Name = "Lion1" };
+        var updateDefinition1 = Builders<Lion>.Update
+            .SetOnInsert(l => l.Id, 1)
+            .Set(l => l.Name, lion1.Name);
+        collection.OfType<Lion>().FindOneAndUpdate(
+            f => f.Name == lion1.Name,
+            updateDefinition1,
+            new FindOneAndUpdateOptions<Lion> { IsUpsert = true });
+
+        var result = collection.AsQueryable().As(BsonDocumentSerializer.Instance).Single();
+        result.Should().Be(
+            """
+            {
+                _id : 1,
+                Name : "Lion1",
+                _t : ["Animal", "Cat", "Lion"]
+            }
+            """);
+    }
+
+    [Fact]
+    public void UpdateOne_should_use_correct_discriminator()
+    {
+        var collection = Fixture.Collection;
+
+        var lion2 = new Lion { Id = 2, Name = "Lion2" };
+        var updateDefinition2 = Builders<Lion>.Update
+            .SetOnInsert(l => l.Id, lion2.Id)
+            .Set(l => l.Name, lion2.Name);
+        collection.OfType<Lion>().UpdateOne(
+            f => f.Name == lion2.Name,
+            updateDefinition2,
+            new UpdateOptions<Lion> { IsUpsert = true });
+
+        var result = collection.AsQueryable().As(BsonDocumentSerializer.Instance).Single();
+        result.Should().Be(
+            """
+            {
+                _id : 2,
+                Name : "Lion2",
+                _t : ["Animal", "Cat", "Lion"]
+            }
+            """);
+    }
+
+    [BsonDiscriminator(RootClass = true)]
+    [BsonKnownTypes(typeof(Cat), typeof(Dog))]
+    public class Animal
+    {
+        public int Id { get; set; }
+    }
+
+    [BsonKnownTypes(typeof(Lion), typeof(Tiger))]
+    public class Cat : Animal
+    {
+    }
+
+    public class Dog : Animal
+    {
+    }
+
+    public class Lion : Cat
+    {
+        public string Name { get; set; }
+    }
+    public class Tiger : Cat
+    {
+    }
+
+    public sealed class ClassFixture : MongoCollectionFixture<Animal>
+    {
+        public override bool InitializeDataBeforeEachTestCase => true;
+
+        protected override IEnumerable<Animal> InitialData => null;
+        // [
+        //     new Animal { }
+        // ];
+    }
+}