Unknown Summary
Using LINQ3 If Project will produce a null result element an exception will be thrown:
_System.InvalidOperationException: ReadName can only be called when State is Name, not when State is EndOfDocument. at MongoDB.Bson.IO.BsonReader.ThrowInvalidState(String methodName, BsonReaderState[] validStates) at MongoDB.Bson.IO.BsonBinaryReader.ReadName(INameDecoder nameDecoder) at MongoDB.Bson.IO.IBsonReaderExtensions.ReadName(IBsonReader reader) at MongoDB.Bson.IO.IBsonReaderExtensions.VerifyName(IBsonReader reader, String expectedName) at MongoDB.Bson.IO.IBsonReaderExtensions.ReadName(IBsonReader reader, String name) at MongoDB.Driver.Linq.Linq3Implementation.Serializers.WrappedValueSerializer`1.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer`1 serializer, BsonDeserializationContext context) at MongoDB.Driver.Core.Operations.CursorBatchDeserializationHelper.DeserializeBatch[TDocument](RawBsonArray batch, IBsonSerializer`1 documentSerializer, MessageEncoderSettings messageEncoderSettings) at MongoDB.Driver.Core.Operations.FindOperation`1.CreateFirstCursorBatch(BsonDocument cursorDocument) at MongoDB.Driver.Core.Operations.FindOperation`1.CreateCursor(IChannelSourceHandle channelSource, IChannelHandle channel, BsonDocument commandResult) at MongoDB.Driver.Core.Operations.FindOperation`1.ExecuteAsync(RetryableReadContext context, CancellationToken cancellationToken) at MongoDB.Driver.Core.Operations.FindOperation`1.ExecuteAsync(IReadBinding binding, CancellationToken cancellationToken) at MongoDB.Driver.OperationExecutor.ExecuteReadOperationAsync[TResult](IReadBinding binding, IReadOperation`1 operation, CancellationToken cancellationToken) at MongoDB.Driver.MongoCollectionImpl`1.ExecuteReadOperationAsync[TResult](IClientSessionHandle session, IReadOperation`1 operation, ReadPreference readPreference, CancellationToken cancellationToken) at MongoDB.Driver.MongoCollectionImpl`1.UsingImplicitSessionAsync[TResult](Func`2 funcAsync, CancellationToken cancellationToken) at MongoDB.Driver.IAsyncCursorSourceExtensions.ToListAsync[TDocument](IAsyncCursorSource`1 source, CancellationToken cancellationToken)_
LINQ2 adds null elements in the result.
How to Reproduce
define a class with a nullable type property
class TestData { [BsonId] [BsonRepresentation(BsonType.ObjectId)] public string _id { get; set; } public double? DoubleNullableValue { get; set; } }
Insert elements with null value for DoubleNullableValue
_var mongoUrl = MongoUrl.Create("mongodb://localhost:27017");
var clientSettings = MongoClientSettings.FromUrl(mongoUrl);
clientSettings.LinqProvider = LinqProvider.V3;
var mongoC = new MongoClient(clientSettings);
var collection = mongoC.GetDatabase("Tests").GetCollection<TestData>("NullableDataTest");
//Insert test samples
await collection.InsertManyAsync(new []
{
new TestData
,
new TestData()
});_
Make a find thath will not exlude the null values and projects them
__
await collection.Find(_ => true).Project(t => t.DoubleNullableValue).ToListAsync();
The above exception will be thrown.
Additional Background
.NET6 Console project reproducing bug attached. (Ensure {}mongoUrl).