CSHARP-4062: Projection of constant with no known serializer is not supported.

Author: rstam

src/MongoDB.Driver/Linq/Linq3Implementation/Serializers/KnownSerializers/KnownSerializersRegistry.cs

@@ -40,7 +40,7 @@ public IBsonSerializer GetSerializer(Expression expression, IBsonSerializer defa
             var possibleSerializers = _registry.TryGetValue(expression, out var knownSerializers) ? knownSerializers.GetPossibleSerializers(expressionType) : new HashSet<IBsonSerializer>();
             return possibleSerializers.Count switch
             {
-                0 => defaultSerializer ?? throw new InvalidOperationException($"Cannot find serializer for {expression}."),
+                0 => defaultSerializer ?? BsonSerializer.LookupSerializer(expressionType), // sometimes there is no known serializer from the context (e.g. CSHARP-4062)
                 > 1 => throw new InvalidOperationException($"More than one possible serializer found for {expression}."),
                 _ => possibleSerializers.First()
             };

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Jira/CSharp4062Tests.cs

@@ -0,0 +1,125 @@
+/* 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.Linq;
+using MongoDB.Bson;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests.Jira
+{
+    public class CSharp4062Tests : Linq3IntegrationTest
+    {
+        [Fact]
+        public void Project_anonymous_class_constant_should_work()
+        {
+            var collection = GetCollection<BsonDocument>();
+            var aggregate = collection.Aggregate()
+                .Project(x => new { R = true });
+
+            var stages = Translate(collection, aggregate);
+
+            AssertStages(stages, "{ $project : { _v : { R : true }, _id : 0 } }");
+        }
+
+        [Fact]
+        public void Project_non_anonymous_class_constant_should_work()
+        {
+            var collection = GetCollection<BsonDocument>();
+            var aggregate = collection.Aggregate()
+                .Project(x => new C { R = true });
+
+            var stages = Translate(collection, aggregate);
+
+            AssertStages(stages, "{ $project : { _v : { R : true }, _id : 0 } }");
+        }
+
+        [Fact]
+        public void Project_boolean_constant_should_work()
+        {
+            var collection = GetCollection<BsonDocument>();
+            var aggregate = collection.Aggregate()
+                .Project(x => true);
+
+            var stages = Translate(collection, aggregate);
+
+            AssertStages(stages, "{ $project : { _v : true, _id : 0 } }");
+        }
+
+        [Fact]
+        public void Project_int_constant_should_work()
+        {
+            var collection = GetCollection<BsonDocument>();
+            var aggregate = collection.Aggregate()
+                .Project(x => 1);
+
+            var stages = Translate(collection, aggregate);
+
+            AssertStages(stages, "{ $project : { _v : 1, _id : 0 } }");
+        }
+
+        [Fact]
+        public void Select_anonymous_class_constant_should_work()
+        {
+            var collection = GetCollection<BsonDocument>();
+            var queryable = collection.AsQueryable()
+                .Select(x => new { R = true });
+
+            var stages = Translate(collection, queryable);
+
+            AssertStages(stages, "{ $project : { _v : { R : true }, _id : 0 } }");
+        }
+
+        [Fact]
+        public void Select_non_anonymous_class_constant_should_work()
+        {
+            var collection = GetCollection<BsonDocument>();
+            var queryable = collection.AsQueryable()
+                .Select(x => new C { R = true });
+
+            var stages = Translate(collection, queryable);
+
+            AssertStages(stages, "{ $project : { _v : { R : true }, _id : 0 } }");
+        }
+
+        [Fact]
+        public void Select_boolean_constant_should_work()
+        {
+            var collection = GetCollection<BsonDocument>();
+            var queryable = collection.AsQueryable()
+                .Select(x => true);
+
+            var stages = Translate(collection, queryable);
+
+            AssertStages(stages, "{ $project : { _v : true, _id : 0 } }");
+        }
+
+        [Fact]
+        public void Select_int_constant_should_work()
+        {
+            var collection = GetCollection<BsonDocument>();
+            var queryable = collection.AsQueryable()
+                .Select(x => 1);
+
+            var stages = Translate(collection, queryable);
+
+            AssertStages(stages, "{ $project : { _v : 1, _id : 0 } }");
+        }
+
+        private class C
+        {
+            public bool R { get; set; }
+        }
+    }
+}