CSHARP-4609: Replace DowncastingSerializer with more permissive ConvertIfPossibleSerializer when rendering values associated with a FieldDefnition.

Author: rstam

src/MongoDB.Bson/Serialization/Serializers/DowncastingSerializer.cs

@@ -17,6 +17,27 @@
 
 namespace MongoDB.Bson.Serialization.Serializers
 {
+    /// <summary>
+    /// An interface implemented by DowncastingSerializer.
+    /// </summary>
+    public interface IDowncastingSerializer
+    {
+        /// <summary>
+        /// The base type that the serializer will downcast from.
+        /// </summary>
+        Type BaseType { get; }
+
+        /// <summary>
+        /// The serializer for the derived type.
+        /// </summary>
+        IBsonSerializer DerivedSerializer { get; }
+
+        /// <summary>
+        /// The derived type that the serializer will downcast to.
+        /// </summary>
+        Type DerivedType { get; }
+    }
+
     /// <summary>
     /// Static factory class for DowncastingSerializer.
     /// </summary>
@@ -44,7 +65,7 @@ public static IBsonSerializer Create(
     /// </summary>
     /// <typeparam name="TBase">The base type.</typeparam>
     /// <typeparam name="TDerived">The derived type.</typeparam>
-    public class DowncastingSerializer<TBase, TDerived> : SerializerBase<TBase>, IBsonDocumentSerializer
+    public class DowncastingSerializer<TBase, TDerived> : SerializerBase<TBase>, IBsonDocumentSerializer, IDowncastingSerializer
         where TDerived : TBase
     {
         private readonly IBsonSerializer<TDerived> _derivedSerializer;
@@ -59,6 +80,17 @@ public DowncastingSerializer(IBsonSerializer<TDerived> derivedSerializer)
             _derivedSerializer = derivedSerializer ?? throw new ArgumentNullException(nameof(derivedSerializer));
         }
 
+        /// <inheritdoc/>
+        public Type BaseType => typeof(TBase);
+
+        /// <inheritdoc/>
+        public IBsonSerializer<TDerived> DerivedSerializer => _derivedSerializer;
+
+        IBsonSerializer IDowncastingSerializer.DerivedSerializer => _derivedSerializer;
+
+        /// <inheritdoc/>
+        public Type DerivedType => typeof(TDerived);
+
         /// <inheritdoc/>
         public override TBase Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
         {

src/MongoDB.Driver/FieldValueSerializerHelper.cs

@@ -38,6 +38,13 @@ public static IBsonSerializer GetSerializerForValueType(IBsonSerializer fieldSer
             // these will normally be equal unless we've removed some Convert(s) that the compiler put in
             if (fieldType == valueType)
             {
+                if (fieldSerializer is IDowncastingSerializer downcastingSerializer)
+                {
+                    var derivedSerializer = downcastingSerializer.DerivedSerializer;
+                    var derivedType = derivedSerializer.ValueType;
+                    return ConvertIfPossibleSerializer.Create(valueType, derivedType, derivedSerializer, serializerRegistry);
+                }
+
                 return fieldSerializer;
             }
 
@@ -54,7 +61,6 @@ public static IBsonSerializer GetSerializerForValueType(IBsonSerializer fieldSer
 
             var fieldTypeInfo = fieldType.GetTypeInfo();
             var fieldSerializerInterfaceType = typeof(IBsonSerializer<>).MakeGenericType(fieldType);
-            var valueTypeInfo = valueType.GetTypeInfo();
 
             // synthesize a NullableSerializer using the field serializer
             if (valueType.IsNullable() && valueType.GetNullableUnderlyingType() == fieldType)
@@ -132,9 +138,7 @@ public static IBsonSerializer GetSerializerForValueType(IBsonSerializer fieldSer
             }
 
             // if we can't return a value serializer based on the field serializer return a converting serializer
-            var convertIfPossibleSerializerType = typeof(ConvertIfPossibleSerializer<,>).MakeGenericType(valueType, fieldType);
-            var convertIfPossibleSerializerConstructor = convertIfPossibleSerializerType.GetTypeInfo().GetConstructor(new[] { fieldSerializerInterfaceType, typeof(IBsonSerializerRegistry) });
-            return (IBsonSerializer)convertIfPossibleSerializerConstructor.Invoke(new object[] { fieldSerializer, serializerRegistry });
+            return ConvertIfPossibleSerializer.Create(valueType, fieldType, fieldSerializer, serializerRegistry);
         }
 
         public static IBsonSerializer GetSerializerForValueType(IBsonSerializer fieldSerializer, IBsonSerializerRegistry serializerRegistry, Type valueType, object value)
@@ -177,6 +181,20 @@ private static IBsonSerializer WithStringRepresentation(IBsonSerializer serializ
         }
 
         // nested types
+        private static class ConvertIfPossibleSerializer
+        {
+            public static IBsonSerializer Create(
+                Type valueType,
+                Type fieldType,
+                IBsonSerializer fieldSerializer,
+                IBsonSerializerRegistry serializerRegistry)
+            {
+                var convertIfPossibleSerializerType = typeof(ConvertIfPossibleSerializer<,>).MakeGenericType(valueType, fieldType);
+                var convertIfPossibleSerializerConstructor = convertIfPossibleSerializerType.GetTypeInfo().GetConstructor(new[] { fieldSerializer.GetType(), typeof(IBsonSerializerRegistry) });
+                return (IBsonSerializer)convertIfPossibleSerializerConstructor.Invoke(new object[] { fieldSerializer, serializerRegistry });
+            }
+        }
+
         private class ConvertIfPossibleSerializer<TFrom, TTo> : SerializerBase<TFrom>
         {
             private readonly IBsonSerializer<TTo> _serializer;

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Jira/CSharp4609Tests.cs

@@ -0,0 +1,63 @@
+/* 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.Linq;
+using System.Linq.Expressions;
+using FluentAssertions;
+using MongoDB.Driver.Linq;
+using MongoDB.TestHelpers.XunitExtensions;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests.Jira
+{
+    public class CSharp4609Tests : Linq3IntegrationTest
+    {
+        [Theory]
+        [ParameterAttributeData]
+        public void Project_dictionary_value_should_work(
+            [Values(LinqProvider.V2, LinqProvider.V3)] LinqProvider linqProvider)
+        {
+            var collection = CreateCollection(linqProvider);
+            Expression<Func<MeasurementDetails, object>> field = x => x.CreationDate;
+            var myValue = "2023-04-13T01:02:03Z";
+            var filter = Builders<MeasurementDetails>.Filter.Lt(field, myValue);
+
+            var find = collection.Find(filter);
+
+            var translatedFilter = TranslateFilter(collection, filter);
+            translatedFilter.Should().Be("{ CreationDate : { $lt : ISODate('2023-04-13T01:02:03Z') } }");
+
+            var results = find.ToList();
+            results.Select(r => r.Id).Should().Equal(1);
+        }
+
+        private IMongoCollection<MeasurementDetails> CreateCollection(LinqProvider linqProvider)
+        {
+            var collection = GetCollection<MeasurementDetails>("test", linqProvider);
+            CreateCollection(
+                collection,
+                new MeasurementDetails { Id = 1, CreationDate = new DateTime(2023, 04, 13, 1, 2, 2, DateTimeKind.Utc) },
+                new MeasurementDetails { Id = 2, CreationDate = new DateTime(2023, 04, 13, 1, 2, 3, DateTimeKind.Utc) });
+            return collection;
+        }
+
+        private class MeasurementDetails
+        {
+            public int Id { get; set; }
+            public DateTime CreationDate { get; set; }
+        }
+    }
+}

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Linq3IntegrationTest.cs

@@ -20,7 +20,6 @@
 using MongoDB.Bson.Serialization;
 using MongoDB.Driver.Linq;
 using MongoDB.Driver.Linq.Linq3Implementation;
-using MongoDB.Driver.Linq.Linq3Implementation.Misc;
 using MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToExecutableQueryTranslators;
 
 namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests