MongoDB C# driver InvalidOperationException when accessing ID on newly saved object

Question

I'm saving an item in MongoDB using the C# driver V2.9.3.

I'm seeing the following exception being thrown occasionally (although once its happened once it appears to be more lightly to happen again).

System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
  at System.Collections.Generic.Dictionary`2.Enumerator.MoveNext()
  at MongoDB.Bson.Serialization.Serializers.DictionarySerializerBase`3.SerializeDocumentRepresentation(BsonSerializationContext context, TDictionary value)
  at MongoDB.Bson.Serialization.Serializers.ClassSerializerBase`1.Serialize(BsonSerializationContext context, BsonSerializationArgs args, TValue value)
  at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Serialize(IBsonSerializer serializer, BsonSerializationContext context, Object value)
  at MongoDB.Bson.Serialization.BsonClassMapSerializer`1.SerializeClass(BsonSerializationContext context, BsonSerializationArgs args, TClass document)
  at MongoDB.Bson.Serialization.BsonClassMapSerializer`1.Serialize(BsonSerializationContext context, BsonSerializationArgs args, TClass value)
  at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Serialize(IBsonSerializer serializer, BsonSerializationContext context, Object value)
  at MongoDB.Bson.Serialization.Serializers.BsonValueSerializerBase`1.Serialize(BsonSerializationContext context, BsonSerializationArgs args, TBsonValue value)
  at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Serialize(IBsonSerializer serializer, BsonSerializationContext context, Object value)
  at MongoDB.Bson.Serialization.Serializers.BsonValueSerializerBase`1.Serialize(BsonSerializationContext context, BsonSerializationArgs args, TBsonValue value)
  at MongoDB.Driver.Core.WireProtocol.Messages.Encoders.BinaryEncoders.CommandMessageBinaryEncoder.WriteType1Section(BsonBinaryWriter writer, Type1CommandMessageSection section, Int64 messageStartPosition)
  at MongoDB.Driver.Core.WireProtocol.Messages.Encoders.BinaryEncoders.CommandMessageBinaryEncoder.WriteSections(BsonBinaryWriter writer, IEnumerable`1 sections, Int64 messageStartPosition)
  at MongoDB.Driver.Core.WireProtocol.Messages.Encoders.BinaryEncoders.CommandMessageBinaryEncoder.WriteMessage(CommandMessage message)
  at MongoDB.Driver.Core.Connections.BinaryConnection.SendMessagesHelper.EncodeMessages(CancellationToken cancellationToken, List`1& sentMessages)
  at MongoDB.Driver.Core.Connections.BinaryConnection.SendMessagesAsync(IEnumerable`1 messages, MessageEncoderSettings messageEncoderSettings, CancellationToken cancellationToken)
  at MongoDB.Driver.Core.WireProtocol.CommandUsingCommandMessageWireProtocol`1.ExecuteAsync(IConnection connection, CancellationToken cancellationToken)
  at MongoDB.Driver.Core.Servers.Server.ServerChannel.ExecuteProtocolAsync[TResult](IWireProtocol`1 protocol, CancellationToken cancellationToken)
  at MongoDB.Driver.Core.Operations.RetryableWriteOperationExecutor.ExecuteAsync[TResult](IRetryableWriteOperation`1 operation, RetryableWriteContext context, CancellationToken cancellationToken)
  at MongoDB.Driver.Core.Operations.BulkUnmixedWriteOperationBase`1.ExecuteBatchAsync(RetryableWriteContext context, Batch batch, CancellationToken cancellationToken)
  at MongoDB.Driver.Core.Operations.BulkUnmixedWriteOperationBase`1.ExecuteBatchesAsync(RetryableWriteContext context, CancellationToken cancellationToken)
  at MongoDB.Driver.Core.Operations.BulkMixedWriteOperation.ExecuteBatchAsync(RetryableWriteContext context, Batch batch, CancellationToken cancellationToken)
  at MongoDB.Driver.Core.Operations.BulkMixedWriteOperation.ExecuteAsync(IWriteBinding binding, CancellationToken cancellationToken)
  at MongoDB.Driver.OperationExecutor.ExecuteWriteOperationAsync[TResult](IWriteBinding binding, IWriteOperation`1 operation, CancellationToken cancellationToken)
  at MongoDB.Driver.MongoCollectionImpl`1.ExecuteWriteOperationAsync[TResult](IClientSessionHandle session, IWriteOperation`1 operation, CancellationToken cancellationToken)
  at MongoDB.Driver.MongoCollectionImpl`1.BulkWriteAsync(IClientSessionHandle session, IEnumerable`1 requests, BulkWriteOptions options, CancellationToken cancellationToken)
  at MongoDB.Driver.MongoCollectionImpl`1.UsingImplicitSessionAsync[TResult](Func`2 funcAsync, CancellationToken cancellationToken)
  at MongoDB.Driver.MongoCollectionBase`1.InsertOneAsync(TDocument document, InsertOneOptions options, Func`3 bulkWriteAsync)
  at MyApp.Program.MongoDbResultSaver.Save(PhishingResult result, IEmailHolder email) line 107
  at MyApp.Program.Services.MongoDbResultSaver.Save(PhishingResult result, IEmailHolder email) line 121

See below for my redacted code

            try
            {
                var obj= new MyDbObject()
                {
                    ID = Guid.NewGuid().ToString(),
            // meny propertys including objects, and lists of objects

                };

                var metaCollection = db.GetCollection<MyDbObject>("MyDbObject");

                await metaCollection.InsertOneAsync(obj);
                _logger.Info("Saved with ID " + obj.ID);//line 107 in stack trace where the error is coming from
            }
            catch (Exception e)
            {
                _logger.Error($"Failed to save metastore with error {e}");
                throw;//line 121 in stacktrace where the error is being rethrown
            }

And relevant part of object definition

  [BsonIgnoreExtraElements]
  public class MyDbObject
  {
    [BsonId]
    public string ID { get; set; }

    [BsonElement("etc")]
//etc
  }

Any help is appreciated, we have only observed this happening in production with mongodb atlas M10 instance as the server.

This is going to be the tricky part.. can you reproduce it? If not, how can any of the solutions being provided will help you ? — Jawad, Dec 18 '19 at 22:07
Does this answer your question? [Collection was modified; enumeration operation may not execute](https://stackoverflow.com/questions/604831/collection-was-modified-enumeration-operation-may-not-execute) — Jawad, Dec 18 '19 at 22:17

score 0 · Answer 1 · answered Dec 16 '19 at 12:16

You can use ObjectId for unique identifier of document.

try
{
    var obj= new MyDbObject()
    {
        ID = ObjectId.GenerateNewId(),
        // many properties including objects, and lists of objects

    };

    var metaCollection = db.GetCollection<MyDbObject>("MyDbObject");

    await metaCollection.InsertOneAsync(obj);
    _logger.Info("Saved with ID " + obj.ID);//line 107 in stack trace where the error is coming from
}
catch (Exception e)
{
    _logger.Error($"Failed to save metastore with error {e}");
    throw;//line 121 in stacktrace where the error is being rethrown
}

Object model will be,

[BsonIgnoreExtraElements]
public class MyDbObject
{
    [BsonId]
    public ObjectId ID { get; set; }

    [BsonElement("etc")]
//etc
  }

The _id field can be any type, even if it is usualy an objectId see here for example https://stackoverflow.com/a/6069830/1658329. And given that this code works 99% of this time i dont think that is the issue. — Tom Hazell, Dec 16 '19 at 14:25
Please do provide the loop that you are going over that makes the call for inserting the document. — Jawad, Dec 18 '19 at 22:13

score 0 · Answer 2 · answered Dec 19 '19 at 23:05

0

Turns out the issue is that I had a task that had timed out with a reference to the object I was saving, it happened to complete and add an item to the a dictionary property at the same time the item was saving in Mogo.

answered Dec 19 '19 at 23:05

Tom Hazell

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MongoDB C# driver InvalidOperationException when accessing ID on newly saved object

2 Answers2