Mongo DB BsonSerializationException when using IAggregateFluentExtensions.GraphLookup() with GUIDs

Question

I am storing trees of nodes in a (local) Mongo database, using GUIDs as the EntityId and ParentEntityId for each node. I am trying to retrieve nodes using IAggregateFluentExtensions.GraphLookup(). The call to GraphLookup() is throwing:

MongoDB.Bson.BsonSerializationException : GuidSerializer cannot deserialize a Guid when GuidRepresentation is Unspecified.

Why is it throwing this exception? GUID handling is configured for V3, per the code below. It has been working for storing & retrieving other types in the same database that have GUIDs on them.

Here is my Entity class for each Node:

public class TestEntity
{
    [BsonId]
    public ObjectId Id { get; set;}

    [BsonGuidRepresentation(GuidRepresentation.Standard)]
    public Guid EntityId { get; set; }

    [BsonGuidRepresentation(GuidRepresentation.Standard)]
    public Guid ParentEntityId { get; set; }

    public string Name { get; set; }
}

Here is a simplified version of the repository code, which throws the exception, on the GraphLookup() line.

public async Task<List<object>> DoGraphLookup()
{
    BsonDefaults.GuidRepresentationMode = GuidRepresentationMode.V3;
    BsonSerializer.RegisterSerializer(new GuidSerializer(GuidRepresentation.Standard));

    MongoClientSettings mongoClientSettings = MongoClientSettings.FromConnectionString("mongodb://HOSTNAME:27017");
    MongoClient mongoClient = new MongoClient(mongoClientSettings);

    IMongoDatabase database = mongoClient.GetDatabase("DATABASENAME");

    IMongoCollection<TestEntity> collection = database.GetCollection<TestEntity>("COLLECTIONNAME");

    List<object> result = await collection
        .Aggregate()
        //.Match(c => c.Name == "MatchName")
        .GraphLookup<TestEntity, Guid, Guid, Guid, TestEntity, IEnumerable<TestEntity>, object>(
        from: collection,
        startWith: $"${nameof(TestEntity.EntityId)}",
        connectFromField: nameof(TestEntity.ParentEntityId),
        connectToField: nameof(TestEntity.EntityId),
        @as: "BreadCrumb",
        depthField: "order")
        .ToListAsync();

    return result;
}

I'm using C# .NET Core 3.1, with these Nuget packages in my project:

MongoDB.Bson 2.13.1
MongoDB.Driver 2.13.1
MongoDB.Driver.Core 2.13.1

DB Looks like this:

Database contents

--- EDIT --- Exception stack trace:

MyApplication.Repositories.TreeOfNodesRepository.DoGraphLookup: Outcome: Failed Error Message: MongoDB.Bson.BsonSerializationException : GuidSerializer cannot deserialize a Guid when GuidRepresentation is Unspecified. Stack Trace: at MongoDB.Bson.Serialization.Serializers.GuidSerializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer1 serializer, BsonDeserializationContext context) at MongoDB.Bson.Serialization.Serializers.ObjectSerializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer1 serializer, BsonDeserializationContext context) at MongoDB.Bson.Serialization.Serializers.DynamicDocumentBaseSerializer1.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.Serializers.SerializerBase1.MongoDB.Bson.Serialization.IBsonSerializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.Serializers.ObjectSerializer.DeserializeDiscriminatedValue(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.Serializers.ObjectSerializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer1 serializer, BsonDeserializationContext context) at MongoDB.Bson.Serialization.Serializers.EnumerableSerializerBase2.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer1 serializer, BsonDeserializationContext context) at MongoDB.Driver.Core.Operations.AggregateOperation1.CursorDeserializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer1 serializer, BsonDeserializationContext context) at MongoDB.Driver.Core.Operations.AggregateOperation1.AggregateResultDeserializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer1 serializer, BsonDeserializationContext context) at MongoDB.Driver.Core.WireProtocol.CommandUsingCommandMessageWireProtocol1.ProcessResponse(ConnectionId connectionId, CommandMessage responseMessage) at MongoDB.Driver.Core.WireProtocol.CommandUsingCommandMessageWireProtocol1.ExecuteAsync(IConnection connection, CancellationToken cancellationToken) at MongoDB.Driver.Core.Servers.Server.ServerChannel.ExecuteProtocolAsync[TResult](IWireProtocol1 protocol, ICoreSession session, CancellationToken cancellationToken) at MongoDB.Driver.Core.Operations.RetryableReadOperationExecutor.ExecuteAsync[TResult](IRetryableReadOperation1 operation, RetryableReadContext context, CancellationToken cancellationToken) at MongoDB.Driver.Core.Operations.ReadCommandOperation1.ExecuteAsync(RetryableReadContext context, CancellationToken cancellationToken) at MongoDB.Driver.Core.Operations.AggregateOperation1.ExecuteAsync(RetryableReadContext context, CancellationToken cancellationToken) at MongoDB.Driver.Core.Operations.AggregateOperation1.ExecuteAsync(IReadBinding binding, CancellationToken cancellationToken) at MongoDB.Driver.OperationExecutor.ExecuteReadOperationAsync[TResult](IReadBinding binding, IReadOperation1 operation, CancellationToken cancellationToken) at MongoDB.Driver.MongoCollectionImpl1.ExecuteReadOperationAsync[TResult](IClientSessionHandle session, IReadOperation1 operation, ReadPreference readPreference, CancellationToken cancellationToken) at MongoDB.Driver.MongoCollectionImpl1.AggregateAsync[TResult](IClientSessionHandle session, PipelineDefinition2 pipeline, AggregateOptions options, CancellationToken cancellationToken) at MongoDB.Driver.MongoCollectionImpl1.UsingImplicitSessionAsync[TResult](Func2 funcAsync, CancellationToken cancellationToken) at MongoDB.Driver.IAsyncCursorSourceExtensions.ToListAsync[TDocument](IAsyncCursorSource1 source, CancellationToken cancellationToken) at MyApplication.Repositories.TreeOfNodesRepository.DoGraphLookup() in c:\Source\saasem\CodeGenerator\Tests\CodeGenerator.ApplicationStore.Tests\Repositories\GraphcLookupTest.cs:line 45 at NUnit.Framework.Internal.TaskAwaitAdapter.GenericAdapter1.BlockUntilCompleted() at NUnit.Framework.Internal.MessagePumpStrategy.NoMessagePumpStrategy.WaitForCompletion(AwaitAdapter awaiter) at NUnit.Framework.Internal.AsyncToSyncAdapter.Await(Func1 invoke) at NUnit.Framework.Internal.Commands.TestMethodCommand.RunTestMethod(TestExecutionContext context) at NUnit.Framework.Internal.Commands.TestMethodCommand.Execute(TestExecutionContext context) at NUnit.Framework.Internal.Execution.SimpleWorkItem.<>c__DisplayClass4_0.b__0() at NUnit.Framework.Internal.ContextUtils.<>c__DisplayClass1_01.<DoIsolated>b__0(Object _) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) --- End of stack trace from previous location --- at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at NUnit.Framework.Internal.ContextUtils.DoIsolated(ContextCallback callback, Object state) at NUnit.Framework.Internal.ContextUtils.DoIsolated[T](Func1 func) at NUnit.Framework.Internal.Execution.SimpleWorkItem.PerformWork()

A stack trace might help others to find a solution to your problem. — Richard
– Richard, Commented Aug 24, 2021 at 6:23
Was there any solution to this? I ran in the same problem... — Marc Reitec
– Marc Reitec, Commented Feb 17 at 7:51

Marc Reitec · Accepted Answer · 2025-02-20 07:01:29Z

0

With the help of MongoDB support I was able to solve it by adding the following lines on initialisazion:

BsonSerializer.RegisterSerializer(new GuidSerializer(GuidRepresentation.Standard));

var objectSerializer = new ObjectSerializer(BsonSerializer.LookupDiscriminatorConvention(typeof(object)), GuidRepresentation.Standard);
BsonSerializer.RegisterSerializer(objectSerializer);

All credits go to MongoDB Support!

answered Feb 20 at 7:01

Marc Reitec

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